Cosmic microwave background constraints on cosmological models with large-scale isotropy breaking
Authors: Haoxuan Zheng, Emory F. Bunn
arXiv:1003.5548v1
Several anomalies appear to be present in the large-angle cosmic microwave background (CMB) anisotropy maps of WMAP, including the alignment of large-scale multipoles and a hemispheric asymmetry. Models in which isotropy is spontaneously broken (e.g., by a scalar field) have been proposed as explanations for these anomalies, as have models in which a preferred direction is imposed during inflation. We examine models inspired by these, in which isotropy is broken by a multiplicative factor with dipole and/or quadrupole terms. We evaluate the evidence provided by these anomalies using a Bayesian framework, finding that the evidence in favor of the model is generally weak. We also compute approximate changes in estimated cosmological parameters in the broken-isotropy models. Only the overall normalization of the power spectrum is modified significantly.
Cosmic Inflation: How the Universe became locally flat and plentiful
Authors: Juan Garcia-Bellido
arXiv:1003.5292v1
The standard model of cosmology is based on the hot Big Bang theory and the inflationary paradigm. Recent precise observations of the temperature and polarization anisotropies in the cosmic microwave background and the matter distribution in large scale structures like galaxies and clusters confirm the general paradigm and put severe constrains on variations of this simple idea. In this essay I will discuss the epistemological foundations of such a paradigm and speculate on its possible realization within a more fundamental theory.
Physical non-equivalence of the Jordan and Einstein frames
Authors: S. Capozziello, P. Martin-Moruno, C. Rubano
arXiv:1003.5394v1
We show, considering a specific f(R)-gravity model, that the Jordan frame and the Einstein frame are physically non-equivalent, although they are connected by a conformal transformation which yields a mathematical equivalence. Since all the calculations are performed analytically, this non-equivalence is shown in an unambiguous way.
Palatini's cousin: A New Variational Principle
Authors: Hubert F M Goenner
arXiv:1003.5532v1
A variational principle is suggested within Riemannnian geometry, in which an auxiliary metric and the Levi Civita connection are varied independently. The auxiliary metric plays the role of a Lagrange multiplier and introduces non-minimal coupling of matter to the curvature scalar. The field equations are 2nd order PDEs and easier to handle than those following from the so-called Palatini method. Moreover, in contrast to the latter method. no gradients of the matter variables appear. In cosmological modeling, the physics resulting from the new variational principle will differ from the modeling using the Palatini method.
Imperfect fluids, Lorentz violations and Finsler Cosmology
Authors: A.P.Kouretsis, M.Stathakopoulos, P.C.Stavrinos
arXiv:1003.5640v1
We construct a cosmological toy model based on a Finslerian structure of space-time. In particular, we are interested in a specific Finslerian Lorentz violating theory based on a curved version of Glashow's Very Special Relativity. The osculation of a Finslerian manifold to a Riemannian leads to the limit of Relativistic Cosmology, for a specified observer. The kinematical equations of motion are affected by local anisotropies. Seeds of Lorentz Violations may trigger density inhomogeneities to the cosmological fluid.
Monday, March 29, 2010
arXiv: 29 Mar 2010
The Dependence of Type Ia Supernova Luminosities on their Host Galaxies
Authors: M. Sullivan, A. Conley, D. A. Howell, J. D. Neill, P. Astier, C. Balland, S. Basa, R. G. Carlberg, D. Fouchez, J. Guy, D. Hardin, I. M. Hook, R. Pain, N. Palanque-Delabrouille, K. M. Perrett, C. J. Pritchet, N. Regnault, J. Rich, V. Ruhlmann-Kleider, S. Baumont, E. Hsiao, T. Kronborg, C. Lidman, S. Perlmutter, E. S. Walker
arXiv:1003.5119v1
(Abridged) Precision cosmology with Type Ia supernovae (SNe Ia) makes use of the fact that SN Ia luminosities depend on their light-curve shapes and colours. Using Supernova Legacy Survey (SNLS) and other data, we show that there is an additional dependence on the global characteristics of their host galaxies: events of the same light-curve shape and colour are, on average, 0.08mag (~4.0sigma) brighter in massive host galaxies (presumably metal-rich) and galaxies with low specific star-formation rates (sSFR). SNe Ia in galaxies with a low sSFR also have a smaller slope ("beta") between their luminosities and colours with ~2.7sigma significance, and a smaller scatter on SN Ia Hubble diagrams (at 95% confidence), though the significance of these effects is dependent on the reddest SNe. SN Ia colours are similar between low-mass and high-mass hosts, leading us to interpret their luminosity differences as an intrinsic property of the SNe and not of some external factor such as dust. If the host stellar mass is interpreted as a metallicity indicator, the luminosity trends are in qualitative agreement with theoretical predictions. We show that the average stellar mass, and therefore the average metallicity, of our SN Ia host galaxies decreases with redshift. The SN Ia luminosity differences consequently introduce a systematic error in cosmological analyses, comparable to the current statistical uncertainties on parameters such as w. We show that the use of two SN Ia absolute magnitudes, one for events in high-mass (metal-rich) galaxies, and one for events in low-mass (metal-poor) galaxies, adequately corrects for the differences. Cosmological fits incorporating these terms give a significant reduction in chi^2 (3.8-4.5sigma). We conclude that future SN Ia cosmological analyses should use a correction of this (or similar) form to control demographic shifts in the galaxy population.
A Universe without Dark Energy and Dark Matter
Authors: Shlomo Barak, Elia M. Leibowitz
arXiv:1003.5092v1
The universe has evolved to be a filamentary web of galaxies and large inter-galactic zones of space without matter. The Euclidian nature of the universe indicates that it is not a 3D manifold within space with an extra spatial dimension. This justifies our assumption that the FRW space-time evolves in the inter-galactic zones like separate FRW universes. Thus we do not necessarily have to consider the entirety of the universe. Our assumption enables us to prove that: -In the current epoch, space in the intergalactic zones expands at a constant rate. -In and around galaxies, space expansion is inhibited. With these results, and an extended Gauss Theorem for a deformed space, we show that there is no need for the hypothetical Dark Energy (DE) and Dark Matter (DM) to explain phenomena attributed to them.
$f(R)$ theory and geometric origin of the dark sector in Horava-Lifshitz gravity
Authors: Anzhong Wang
arXiv:1003.5152v1
$f(R)$ theory in the framework of Horava-Lifshitz quantum gravity with projectability but without detailed balance condition is investigated, and conditions for the spin-0 graviton to be free of ghosts and instability are studied. The requirement that the theory reduce to general relativity in IR makes the scalar mode unstable in the Minkowski background but stable in the de Sitter. It is remarkable that the dark sector, dark matter and dark energy, of the universe has a naturally geometric origin in such a setup. Bouncing universes can also be constructed. Scalar perturbations in FRW backgrounds with non-zero curvature are given.
An introduction to the theory of rotating relativistic stars
Authors: Eric Gourgoulhon
arXiv:1003.5015v1
These lecture notes are intended to introduce the theory of rotating stars in general relativity. The focus is put on the theoretical foundations, with a detailed discussion of the spacetime symmetries, the choice of coordinates and the derivation of the equations of structure from Einstein equation. The global properties of rotating stars (mass, angular momentum, redshifts, orbits, etc.) are also introduced.
Higher-order Statistics of Weak Lensing Shear and Flexion
Authors: Dipak Munshi, Joseph Smidt, Alan Heavens, Peter Coles, Asantha Cooray
arXiv:1003.5003v1
Owing to their more extensive sky coverage and tighter control on systematic errors, future deep weak lensing surveys should provide a better statistical picture of the dark matter clustering beyond the level of the power spectrum. In this context, the study of non-Gaussianity induced by gravity can help tighten constraints on the background cosmology by breaking parameter degeneracies, as well as throwing light on the nature of dark matter, dark energy or alternative gravity theories. Analysis of the shear or flexion properties of such maps is more complicated than the simpler case of the convergence due to the spinorial nature of the fields involved. Here we develop analytical tools for the study of higher-order statistics such as the bispectrum (or trispectrum) directly using such maps at different source redshift. The statistics we introduce can be constructed from cumulants of the shear or flexions, involving the cross-correlation of squared and cubic maps at different redshifts. Typically, the low signal-to-noise ratio prevents recovery of the bispectrum or trispectrum mode by mode. We define power spectra associated with each multi- spectra which compresses some of the available information of higher order multispectra. We show how these can be recovered from a noisy observational data even in the presence of arbitrary mask, which introduces mixing between Electric (E-type) and Magnetic (B-type) polarization, in an unbiased way. We also introduce higher order cross-correlators which can cross-correlate lensing shear with different tracers of large scale structures.
Primordial non-Gaussianity from the large scale structure
Authors: Vincent Desjacques, Uros Seljak
arXiv:1003.5020v1
Primordial non-Gaussianity is a potentially powerful discriminant of the physical mechanisms that generated the cosmological fluctuations observed today. Any detection of non-Gaussianity would have profound implications for our understanding of cosmic structure formation. In this paper, we review past and current efforts in the search for primordial non-Gaussianity in the large scale structure of the Universe.
Authors: M. Sullivan, A. Conley, D. A. Howell, J. D. Neill, P. Astier, C. Balland, S. Basa, R. G. Carlberg, D. Fouchez, J. Guy, D. Hardin, I. M. Hook, R. Pain, N. Palanque-Delabrouille, K. M. Perrett, C. J. Pritchet, N. Regnault, J. Rich, V. Ruhlmann-Kleider, S. Baumont, E. Hsiao, T. Kronborg, C. Lidman, S. Perlmutter, E. S. Walker
arXiv:1003.5119v1
(Abridged) Precision cosmology with Type Ia supernovae (SNe Ia) makes use of the fact that SN Ia luminosities depend on their light-curve shapes and colours. Using Supernova Legacy Survey (SNLS) and other data, we show that there is an additional dependence on the global characteristics of their host galaxies: events of the same light-curve shape and colour are, on average, 0.08mag (~4.0sigma) brighter in massive host galaxies (presumably metal-rich) and galaxies with low specific star-formation rates (sSFR). SNe Ia in galaxies with a low sSFR also have a smaller slope ("beta") between their luminosities and colours with ~2.7sigma significance, and a smaller scatter on SN Ia Hubble diagrams (at 95% confidence), though the significance of these effects is dependent on the reddest SNe. SN Ia colours are similar between low-mass and high-mass hosts, leading us to interpret their luminosity differences as an intrinsic property of the SNe and not of some external factor such as dust. If the host stellar mass is interpreted as a metallicity indicator, the luminosity trends are in qualitative agreement with theoretical predictions. We show that the average stellar mass, and therefore the average metallicity, of our SN Ia host galaxies decreases with redshift. The SN Ia luminosity differences consequently introduce a systematic error in cosmological analyses, comparable to the current statistical uncertainties on parameters such as w. We show that the use of two SN Ia absolute magnitudes, one for events in high-mass (metal-rich) galaxies, and one for events in low-mass (metal-poor) galaxies, adequately corrects for the differences. Cosmological fits incorporating these terms give a significant reduction in chi^2 (3.8-4.5sigma). We conclude that future SN Ia cosmological analyses should use a correction of this (or similar) form to control demographic shifts in the galaxy population.
A Universe without Dark Energy and Dark Matter
Authors: Shlomo Barak, Elia M. Leibowitz
arXiv:1003.5092v1
The universe has evolved to be a filamentary web of galaxies and large inter-galactic zones of space without matter. The Euclidian nature of the universe indicates that it is not a 3D manifold within space with an extra spatial dimension. This justifies our assumption that the FRW space-time evolves in the inter-galactic zones like separate FRW universes. Thus we do not necessarily have to consider the entirety of the universe. Our assumption enables us to prove that: -In the current epoch, space in the intergalactic zones expands at a constant rate. -In and around galaxies, space expansion is inhibited. With these results, and an extended Gauss Theorem for a deformed space, we show that there is no need for the hypothetical Dark Energy (DE) and Dark Matter (DM) to explain phenomena attributed to them.
$f(R)$ theory and geometric origin of the dark sector in Horava-Lifshitz gravity
Authors: Anzhong Wang
arXiv:1003.5152v1
$f(R)$ theory in the framework of Horava-Lifshitz quantum gravity with projectability but without detailed balance condition is investigated, and conditions for the spin-0 graviton to be free of ghosts and instability are studied. The requirement that the theory reduce to general relativity in IR makes the scalar mode unstable in the Minkowski background but stable in the de Sitter. It is remarkable that the dark sector, dark matter and dark energy, of the universe has a naturally geometric origin in such a setup. Bouncing universes can also be constructed. Scalar perturbations in FRW backgrounds with non-zero curvature are given.
An introduction to the theory of rotating relativistic stars
Authors: Eric Gourgoulhon
arXiv:1003.5015v1
These lecture notes are intended to introduce the theory of rotating stars in general relativity. The focus is put on the theoretical foundations, with a detailed discussion of the spacetime symmetries, the choice of coordinates and the derivation of the equations of structure from Einstein equation. The global properties of rotating stars (mass, angular momentum, redshifts, orbits, etc.) are also introduced.
Higher-order Statistics of Weak Lensing Shear and Flexion
Authors: Dipak Munshi, Joseph Smidt, Alan Heavens, Peter Coles, Asantha Cooray
arXiv:1003.5003v1
Owing to their more extensive sky coverage and tighter control on systematic errors, future deep weak lensing surveys should provide a better statistical picture of the dark matter clustering beyond the level of the power spectrum. In this context, the study of non-Gaussianity induced by gravity can help tighten constraints on the background cosmology by breaking parameter degeneracies, as well as throwing light on the nature of dark matter, dark energy or alternative gravity theories. Analysis of the shear or flexion properties of such maps is more complicated than the simpler case of the convergence due to the spinorial nature of the fields involved. Here we develop analytical tools for the study of higher-order statistics such as the bispectrum (or trispectrum) directly using such maps at different source redshift. The statistics we introduce can be constructed from cumulants of the shear or flexions, involving the cross-correlation of squared and cubic maps at different redshifts. Typically, the low signal-to-noise ratio prevents recovery of the bispectrum or trispectrum mode by mode. We define power spectra associated with each multi- spectra which compresses some of the available information of higher order multispectra. We show how these can be recovered from a noisy observational data even in the presence of arbitrary mask, which introduces mixing between Electric (E-type) and Magnetic (B-type) polarization, in an unbiased way. We also introduce higher order cross-correlators which can cross-correlate lensing shear with different tracers of large scale structures.
Primordial non-Gaussianity from the large scale structure
Authors: Vincent Desjacques, Uros Seljak
arXiv:1003.5020v1
Primordial non-Gaussianity is a potentially powerful discriminant of the physical mechanisms that generated the cosmological fluctuations observed today. Any detection of non-Gaussianity would have profound implications for our understanding of cosmic structure formation. In this paper, we review past and current efforts in the search for primordial non-Gaussianity in the large scale structure of the Universe.
Saturday, March 27, 2010
arXiv: 26 Mar 2010
Connecting planets around horizontal branch stars with known exoplanets
Authors: Ealeal Bear, Noam Soker
arXiv:1003.4884v1
We study the distribution of exoplanets around main sequence (MS) stars and apply our results to the binary model for the formation of extreme horizontal branch (EHB; sdO; sdB; hot subdwarfs) stars. We conclude that sdB (EHB) stars are prime targets for planets search. We reach this conclusion by noticing that the bimodal distribution of planets around MS stars with respect to the parameter Mp*a^2, is most prominent for MS stars in the mass range 1Mo1AU. Also, if a planet or more are observed at a>1AU, it is possible that a massive planet did survive the common envelope phase, and it is orbiting the EHB with an orbital period of hours do days.
Harrison-Z'eldovich primordial spectrum is consistent with observations
Authors: S. Pandolfi, A. Cooray, E. Giusarma, E. W. Kolb, A. Melchiorri, O. Mena, P. Serra
arXiv:1003.4763v1
Inflation predicts primordial scalar perturbations with a nearly scale-invariant spectrum and a spectral index approximately unity (the Harrison--Zel'dovich (HZ) spectrum). The first important step for inflationary cosmology is to check the consistency of the HZ primordial spectrum with current observations. Recent analyses have claimed that a HZ primordial spectrum is excluded at more than 99% c.l. Here we show that the HZ spectrum is only marginally disfavored if one considers a more general reionization scenario. Data from the Planck mission will settle the issue.
Comparing different realizations of modified Newtonian dynamics: virial theorem and elliptical shells
Authors: HongSheng Zhao, Benoit Famaey
arXiv:1003.4753v1
There exists several modified gravity theories designed to reproduce the empirical Milgrom's formula (MOND). Here we derive analytical results in the context of the static weak-field limit of two of them (BIMOND, leading for a given set of parameters to QUMOND, and TeVeS). In this limit, these theories are constructed to give the same force field for spherical symmetry, but their predictions generally differ out of it. However, for certain realizations of these theories (characterized by specific choices for their free functions), the binding potential-energy of a system is increased, compared to its Newtonian counterpart, by a constant amount independent of the shape and size of the system. In that case, the virial theorem is exactly the same in these two theories, for the whole gravity regime and even outside of spherical symmetry, although the exact force fields are different. We explicitly show this for the force field generated by the two theories inside an elliptical shell. For more general free functions, the virial theorems are however not identical in these two theories. We finally explore the consequences of these analytical results for the two-body force.
Halo model description of the non-linear dark matter power spectrum at $k \gg 1$ Mpc$^{-1}$
Authors: Carlo Giocoli (ZAH/ITA, Heidelberg), Matthias Bartelmann (ZAH/ITA, Heidelberg), Ravi K. Sheth (UPENN, Philadelphia), Marcello Cacciato (The Hebrew University, Jerusalem)
arXiv:1003.4740v1
Accurate knowledge of the non-linear dark-matter power spectrum is important for understanding the large-scale structure of the Universe, the statistics of dark-matter haloes and their evolution, and cosmological gravitational lensing. We analytically model the dark-matter power spectrum and its cross-power spectrum with dark-matter haloes. Our model extends the halo-model formalism, including realistic substructure population within individual dark-matter haloes and the scatter of the concentration parameter at fixed halo mass. We consider three prescriptions for the mass-concentration relation and two for the substructure distribution in dark-matter haloes. We show that this extension of the halo model mainly increases the predicted power on the small scales, and is crucial for proper modeling the cosmological weak-lensing signal due to low-mass haloes. Our extended formalism shows how the halo model approach can be improved in accuracy as one increases the number of ingredients that are calibrated from n-body simulations.
A physical model for the origin of the diffuse cosmic infrared background
Authors: Joshua D. Younger (IAS), Philip F. Hopkins (Berkeley)
arXiv:1003.4733v1
We present a physical model for origin of the cosmic diffuse infrared background (CDIRB). By utilizing the observed stellar mass function and its evolution as input to a semi-empirical model of galaxy formation, we isolate the physics driving diffuse IR emission. The model includes contributions from three primary sources of IR emission: steady-state star formation owing to isolated disk galaxies, interaction-driven bursts of star formation owing to close encounters and mergers, and obscured active galactic nuclei (AGN). We find that most of the CDIRB is produced by equal contributions from objects at z=0.5-1 and z>1, as suggested by recent observations. Of those sources, the vast majority of the emission originates in systems with low to moderate IR luminosities (L_{IR}<10^{12}>2). All star formation in ongoing mergers accounts for <10%> 1 TeV) \gamma-rays, the model provides predictions for the optical depth of the Universe to the most energetic photons. We find that these predictions agree with observations of high-energy cutoffs at TeV energies in nearby blazars, and suggest that while the Universe is extremely optically thick at >10 TeV, the next generation of VHE \gamma-ray telescopes can reasonably expect detections from out to 50-150 Mpc.
Dark Energy, Black Hole Entropy, and the First Precision Measurement in Quantum Gravity
Authors: Niayesh Afshordi (Perimeter/Waterloo)
arXiv:1003.4811v1
The two apparently distinct phenomena of dark energy (or late-time cosmic acceleration) and quantum gravity dominate physics on extremely low, and extremely high energies, but do not seem to have any apparent empirical connection. Nevertheless, the two have a theoretical connection, through the cosmological constant problem. I argue that the finite temperature quantum gravitational corrections to black hole entropy yields a pressure for the gravitational vacuum (or gravitational aether). Assuming that the relative corrections are linear in horizon temperature (i.e. are suppressed by one power of Planck energy), the pressure is comparable to that of dark energy for astrophysical black holes. This implies that the observation of late-time cosmic acceleration may have provided us with the first precision measurement of quantum gravity, i.e. that of black hole entropy.
Advancing Tests of Relativistic Gravity via Laser Ranging to Phobos
Authors: Slava G. Turyshev, William Farr, William M. Folkner, Andre R. Girerd, Hamid Hemmati, Thomas W. Murphy, Jr., James G. Williams, John J. Degnan
arXiv:1003.4961v1
Phobos Laser Ranging (PLR) is a concept for a space mission designed to advance tests of relativistic gravity in the solar system. PLR's primary objective is to measure the curvature of space around the Sun, represented by the Eddington parameter $\gamma$, with an accuracy of two parts in $10^7$, thereby improving today's best result by two orders of magnitude. Other mission goals include measurements of the time-rate-of-change of the gravitational constant, $G$ and of the gravitational inverse square law at 1.5 AU distances--with up to two orders-of-magnitude improvement for each. The science parameters will be estimated using laser ranging measurements of the distance between an Earth station and an active laser transponder on Phobos capable of reaching mm-level range resolution. A transponder on Phobos sending 0.25 mJ, 10 ps pulses at 1 kHz, and receiving asynchronous 1 kHz pulses from earth via a 12 cm aperture will permit links that even at maximum range will exceed a photon per second. A total measurement precision of 50 ps demands a few hundred photons to average to 1 mm (3.3 ps) range precision. Existing satellite laser ranging (SLR) facilities-with appropriate augmentation-will be able to participate in PLR. Since Phobos' orbital period is about 8 hours, each observatory is guaranteed visibility of the Phobos instrument every Earth day. Given the current technology readiness level, PLR could be started in 2011 for launch in 2016 for 3 years of science operations. We discuss the PLR's science objectives, instrument, and mission design. We also present the details of science simulations performed to support the mission's primary objectives.
Authors: Ealeal Bear, Noam Soker
arXiv:1003.4884v1
We study the distribution of exoplanets around main sequence (MS) stars and apply our results to the binary model for the formation of extreme horizontal branch (EHB; sdO; sdB; hot subdwarfs) stars. We conclude that sdB (EHB) stars are prime targets for planets search. We reach this conclusion by noticing that the bimodal distribution of planets around MS stars with respect to the parameter Mp*a^2, is most prominent for MS stars in the mass range 1Mo
Harrison-Z'eldovich primordial spectrum is consistent with observations
Authors: S. Pandolfi, A. Cooray, E. Giusarma, E. W. Kolb, A. Melchiorri, O. Mena, P. Serra
arXiv:1003.4763v1
Inflation predicts primordial scalar perturbations with a nearly scale-invariant spectrum and a spectral index approximately unity (the Harrison--Zel'dovich (HZ) spectrum). The first important step for inflationary cosmology is to check the consistency of the HZ primordial spectrum with current observations. Recent analyses have claimed that a HZ primordial spectrum is excluded at more than 99% c.l. Here we show that the HZ spectrum is only marginally disfavored if one considers a more general reionization scenario. Data from the Planck mission will settle the issue.
Comparing different realizations of modified Newtonian dynamics: virial theorem and elliptical shells
Authors: HongSheng Zhao, Benoit Famaey
arXiv:1003.4753v1
There exists several modified gravity theories designed to reproduce the empirical Milgrom's formula (MOND). Here we derive analytical results in the context of the static weak-field limit of two of them (BIMOND, leading for a given set of parameters to QUMOND, and TeVeS). In this limit, these theories are constructed to give the same force field for spherical symmetry, but their predictions generally differ out of it. However, for certain realizations of these theories (characterized by specific choices for their free functions), the binding potential-energy of a system is increased, compared to its Newtonian counterpart, by a constant amount independent of the shape and size of the system. In that case, the virial theorem is exactly the same in these two theories, for the whole gravity regime and even outside of spherical symmetry, although the exact force fields are different. We explicitly show this for the force field generated by the two theories inside an elliptical shell. For more general free functions, the virial theorems are however not identical in these two theories. We finally explore the consequences of these analytical results for the two-body force.
Halo model description of the non-linear dark matter power spectrum at $k \gg 1$ Mpc$^{-1}$
Authors: Carlo Giocoli (ZAH/ITA, Heidelberg), Matthias Bartelmann (ZAH/ITA, Heidelberg), Ravi K. Sheth (UPENN, Philadelphia), Marcello Cacciato (The Hebrew University, Jerusalem)
arXiv:1003.4740v1
Accurate knowledge of the non-linear dark-matter power spectrum is important for understanding the large-scale structure of the Universe, the statistics of dark-matter haloes and their evolution, and cosmological gravitational lensing. We analytically model the dark-matter power spectrum and its cross-power spectrum with dark-matter haloes. Our model extends the halo-model formalism, including realistic substructure population within individual dark-matter haloes and the scatter of the concentration parameter at fixed halo mass. We consider three prescriptions for the mass-concentration relation and two for the substructure distribution in dark-matter haloes. We show that this extension of the halo model mainly increases the predicted power on the small scales, and is crucial for proper modeling the cosmological weak-lensing signal due to low-mass haloes. Our extended formalism shows how the halo model approach can be improved in accuracy as one increases the number of ingredients that are calibrated from n-body simulations.
A physical model for the origin of the diffuse cosmic infrared background
Authors: Joshua D. Younger (IAS), Philip F. Hopkins (Berkeley)
arXiv:1003.4733v1
We present a physical model for origin of the cosmic diffuse infrared background (CDIRB). By utilizing the observed stellar mass function and its evolution as input to a semi-empirical model of galaxy formation, we isolate the physics driving diffuse IR emission. The model includes contributions from three primary sources of IR emission: steady-state star formation owing to isolated disk galaxies, interaction-driven bursts of star formation owing to close encounters and mergers, and obscured active galactic nuclei (AGN). We find that most of the CDIRB is produced by equal contributions from objects at z=0.5-1 and z>1, as suggested by recent observations. Of those sources, the vast majority of the emission originates in systems with low to moderate IR luminosities (L_{IR}<10^{12}>2). All star formation in ongoing mergers accounts for <10%> 1 TeV) \gamma-rays, the model provides predictions for the optical depth of the Universe to the most energetic photons. We find that these predictions agree with observations of high-energy cutoffs at TeV energies in nearby blazars, and suggest that while the Universe is extremely optically thick at >10 TeV, the next generation of VHE \gamma-ray telescopes can reasonably expect detections from out to 50-150 Mpc.
Dark Energy, Black Hole Entropy, and the First Precision Measurement in Quantum Gravity
Authors: Niayesh Afshordi (Perimeter/Waterloo)
arXiv:1003.4811v1
The two apparently distinct phenomena of dark energy (or late-time cosmic acceleration) and quantum gravity dominate physics on extremely low, and extremely high energies, but do not seem to have any apparent empirical connection. Nevertheless, the two have a theoretical connection, through the cosmological constant problem. I argue that the finite temperature quantum gravitational corrections to black hole entropy yields a pressure for the gravitational vacuum (or gravitational aether). Assuming that the relative corrections are linear in horizon temperature (i.e. are suppressed by one power of Planck energy), the pressure is comparable to that of dark energy for astrophysical black holes. This implies that the observation of late-time cosmic acceleration may have provided us with the first precision measurement of quantum gravity, i.e. that of black hole entropy.
Advancing Tests of Relativistic Gravity via Laser Ranging to Phobos
Authors: Slava G. Turyshev, William Farr, William M. Folkner, Andre R. Girerd, Hamid Hemmati, Thomas W. Murphy, Jr., James G. Williams, John J. Degnan
arXiv:1003.4961v1
Phobos Laser Ranging (PLR) is a concept for a space mission designed to advance tests of relativistic gravity in the solar system. PLR's primary objective is to measure the curvature of space around the Sun, represented by the Eddington parameter $\gamma$, with an accuracy of two parts in $10^7$, thereby improving today's best result by two orders of magnitude. Other mission goals include measurements of the time-rate-of-change of the gravitational constant, $G$ and of the gravitational inverse square law at 1.5 AU distances--with up to two orders-of-magnitude improvement for each. The science parameters will be estimated using laser ranging measurements of the distance between an Earth station and an active laser transponder on Phobos capable of reaching mm-level range resolution. A transponder on Phobos sending 0.25 mJ, 10 ps pulses at 1 kHz, and receiving asynchronous 1 kHz pulses from earth via a 12 cm aperture will permit links that even at maximum range will exceed a photon per second. A total measurement precision of 50 ps demands a few hundred photons to average to 1 mm (3.3 ps) range precision. Existing satellite laser ranging (SLR) facilities-with appropriate augmentation-will be able to participate in PLR. Since Phobos' orbital period is about 8 hours, each observatory is guaranteed visibility of the Phobos instrument every Earth day. Given the current technology readiness level, PLR could be started in 2011 for launch in 2016 for 3 years of science operations. We discuss the PLR's science objectives, instrument, and mission design. We also present the details of science simulations performed to support the mission's primary objectives.
Thursday, March 25, 2010
arXiv: 25 Mar 2010
Constraining $f(R)$ Theories with Temporal Variation of Fine Structure Constant
Authors: Yousef Bisabr
arXiv:1003.4582v1
It is well-known that $f(R)$ theories in Einstein frame is conformally equivalent to quintessence models in which the scalar field minimally couples with gravity. If there exists a matter system in Jordan frame, then it interacts with the scalar field in Einstein frame due to the conformal transformations. This interaction, in general, may lead to changes of fundamental constants. Here we will consider possible time variation of fine structure constant in a general $f(R)$ theory. We will use observational bounds on these variations and argue that it provides a criterion for constraining $f(R)$ models.
New Completeness Methods for Estimating Exoplanet Discoveries by Direct Detection
Authors: Robert A. Brown, Remi Soummer (Space Telescope Science Institute)
arXiv:1003.4700v1
We report new methods for evaluating realistic observing programs that search stars for planets by direct imaging, where observations are selected from an optimized star list, and where stars can be observed multiple times. We show how these methods bring critical insight into the design of the mission & its instruments. These methods provide an estimate of the outcome of the observing program: the probability distribution of discoveries (detection and/or characterization), & an estimate of the occurrence rate of planets (eta). We show that these parameters can be accurately estimated from a single mission simulation, without the need for a complete Monte Carlo mission simulation, & we prove the accuracy of this new approach. Our methods provide the tools to define a mission for a particular science goal, for example defined by the expected number of discoveries and its confidence level. We detail how an optimized star list can be built & how successive observations can be selected. Our approach also provides other critical mission attributes, such as the number of stars expected to be searched, & the probability of zero discoveries. Because these attributes depend strongly on the mission scale, our methods are directly applicable to the design of such future missions & provide guidance to the mission & instrument design based on scientific performance. We illustrate our new methods with practical calculations & exploratory design reference missions for JWST operating with a distant starshade to reduce scattered and diffracted starlight on the focal plane. We estimate that 5 habitable Earth-mass planets would be discovered & characterized with spectroscopy, with a probability of 0 discoveries of 0.004, assuming a small fraction of JWST observing time (7%), eta=0.3, and 70 observing visits, limited by starshade fuel.
Entropic cosmology: a unified model of inflation and late-time acceleration
Authors: Yi-Fu Cai, Jie Liu, Hong Li
arXiv:1003.4526v1
Holography is expected as one of the promising descriptions of quantum general relativity. We present a model for a cosmological system involving two holographic screens and find that their equilibrium exactly yields a standard Friedmann-Robertson-Walker universe. We discuss its cosmological implications by taking into account higher order quantum corrections and quantum nature of horizon evaporation. We will show that this model could give rise to a holographic inflation at high energy scales and realize a late-time acceleration in a unified approach. We test our model from the SN Ia observations and find it can give a nice fit to the data.
Authors: Yousef Bisabr
arXiv:1003.4582v1
It is well-known that $f(R)$ theories in Einstein frame is conformally equivalent to quintessence models in which the scalar field minimally couples with gravity. If there exists a matter system in Jordan frame, then it interacts with the scalar field in Einstein frame due to the conformal transformations. This interaction, in general, may lead to changes of fundamental constants. Here we will consider possible time variation of fine structure constant in a general $f(R)$ theory. We will use observational bounds on these variations and argue that it provides a criterion for constraining $f(R)$ models.
New Completeness Methods for Estimating Exoplanet Discoveries by Direct Detection
Authors: Robert A. Brown, Remi Soummer (Space Telescope Science Institute)
arXiv:1003.4700v1
We report new methods for evaluating realistic observing programs that search stars for planets by direct imaging, where observations are selected from an optimized star list, and where stars can be observed multiple times. We show how these methods bring critical insight into the design of the mission & its instruments. These methods provide an estimate of the outcome of the observing program: the probability distribution of discoveries (detection and/or characterization), & an estimate of the occurrence rate of planets (eta). We show that these parameters can be accurately estimated from a single mission simulation, without the need for a complete Monte Carlo mission simulation, & we prove the accuracy of this new approach. Our methods provide the tools to define a mission for a particular science goal, for example defined by the expected number of discoveries and its confidence level. We detail how an optimized star list can be built & how successive observations can be selected. Our approach also provides other critical mission attributes, such as the number of stars expected to be searched, & the probability of zero discoveries. Because these attributes depend strongly on the mission scale, our methods are directly applicable to the design of such future missions & provide guidance to the mission & instrument design based on scientific performance. We illustrate our new methods with practical calculations & exploratory design reference missions for JWST operating with a distant starshade to reduce scattered and diffracted starlight on the focal plane. We estimate that 5 habitable Earth-mass planets would be discovered & characterized with spectroscopy, with a probability of 0 discoveries of 0.004, assuming a small fraction of JWST observing time (7%), eta=0.3, and 70 observing visits, limited by starshade fuel.
Entropic cosmology: a unified model of inflation and late-time acceleration
Authors: Yi-Fu Cai, Jie Liu, Hong Li
arXiv:1003.4526v1
Holography is expected as one of the promising descriptions of quantum general relativity. We present a model for a cosmological system involving two holographic screens and find that their equilibrium exactly yields a standard Friedmann-Robertson-Walker universe. We discuss its cosmological implications by taking into account higher order quantum corrections and quantum nature of horizon evaporation. We will show that this model could give rise to a holographic inflation at high energy scales and realize a late-time acceleration in a unified approach. We test our model from the SN Ia observations and find it can give a nice fit to the data.
Wednesday, March 24, 2010
arXiv: 24 Mar 2010
TASI Lectures on Cosmic Acceleration
Authors: Rachel Bean
arXiv:1003.4468v1
Lectures from the 2009 Theoretical Advanced Study Institute at Univ. of Colorado
In this series of lectures we review observational evidence for, and theoretical investigations into, cosmic acceleration and dark energy. The notes are in four sections. First I review the basic cosmological formalism to describe the expansion history of the universe and how distance measures are defined. The second section covers the evidence for cosmic acceleration from cosmic distance measurements. Section 3 discusses the theoretical avenues being considered to explain the cosmological observations and section 4 discusses how the growth of inhomogeneities and large scale structure observations might help us pin down the theoretical origin of cosmic acceleration.
Gamma-Ray Bursts Overview
Authors: B. McBreen, S. Foley, L. Hanlon
arXiv:1003.4440v1
It is now more than 40 years since the discovery of gamma-ray bursts (GRBs) and in the last two decades there has been major progress in the observations of bursts, the afterglows and their host galaxies. This recent progress has been fueled by the ability of gamma-ray telescopes to quickly localise GRBs and the rapid follow-up observations with multi-wavelength instruments in space and on the ground. A total of 674 GRBs have been localised to date using the coded aperture masks of the four gamma-ray missions, BeppoSAX, HETE II, INTEGRAL and Swift. As a result there are now high quality observations of more than 100 GRBs, including afterglows and host galaxies, revealing the richness and progress in this field. The observations of GRBs cover more than 20 orders of magnitude in energy, from 10^-5 eV to 10^15 eV and also in two non-electromagnetic channels, neutrinos and gravitational waves. However the continuation of progress relies on space based instruments to detect and rapidly localise GRBs and distribute the coordinates.
Designing Future Dark Energy Space Missions: II. Photometric Redshift of Space Weak Lensing Optimized Survey
Authors: S. Jouvel, J-P. Kneib, G. Bernstein, O. Ilbert, P. Jelinsky, B. Milliard, A. Ealet, C. Schimd, T. Dahlen, S. Arnouts
arXiv:1003.4294v1
Accurate weak-lensing analysis requires not only accurate measurement of galaxy shapes but also precise and unbiased measurement of galaxy redshifts. The photometric redshift technique appears as the only possibility to determine the redshift of the background galaxies used in the weak-lensing analysis. Using the photometric redshift quality, simple shape measurement requirements, and a proper sky model, we explore what could be an optimal weak-lensing dark energy mission based on FoM calculation. We found that photometric redshifts reach their best accurracy for the bulk of the faint galaxy population when filters have a resolution R~3.2. We show that an optimal mission would survey the sky through 8 filters using 2 cameras (visible and near infrared). Assuming a 5-year mission duration, a mirror size of 1.5m, a 0.5deg2 FOV with a visible pixel scale of 0.15", to maximize the Weak Lensing FoM, an optimal exposure time is found to be 4x200s per filter (at the Galactic poles) thus covering ~11000deg2 of the sky over the mission. This work demonstrates that a full account of the observational strategy is required to properly optimize the instrument parameters to maximize the FoM of the future weak-lensing space dark energy mission.
The Cauchy problem for metric-affine f(R)-gravity in presence of a Klein-Gordon scalar field
Authors: S. Capozziello, S. Vignolo
arXiv:1003.4280v1
We study the initial value formulation of metric-affine f(R)-gravity in presence of a Klein-Gordon scalar field acting as source of the field equations. Sufficient conditions for the well-posedness of the Cauchy problem are formulated. This result completes the analysis of the same problem already considered for other sources.
Authors: Rachel Bean
arXiv:1003.4468v1
Lectures from the 2009 Theoretical Advanced Study Institute at Univ. of Colorado
In this series of lectures we review observational evidence for, and theoretical investigations into, cosmic acceleration and dark energy. The notes are in four sections. First I review the basic cosmological formalism to describe the expansion history of the universe and how distance measures are defined. The second section covers the evidence for cosmic acceleration from cosmic distance measurements. Section 3 discusses the theoretical avenues being considered to explain the cosmological observations and section 4 discusses how the growth of inhomogeneities and large scale structure observations might help us pin down the theoretical origin of cosmic acceleration.
Gamma-Ray Bursts Overview
Authors: B. McBreen, S. Foley, L. Hanlon
arXiv:1003.4440v1
It is now more than 40 years since the discovery of gamma-ray bursts (GRBs) and in the last two decades there has been major progress in the observations of bursts, the afterglows and their host galaxies. This recent progress has been fueled by the ability of gamma-ray telescopes to quickly localise GRBs and the rapid follow-up observations with multi-wavelength instruments in space and on the ground. A total of 674 GRBs have been localised to date using the coded aperture masks of the four gamma-ray missions, BeppoSAX, HETE II, INTEGRAL and Swift. As a result there are now high quality observations of more than 100 GRBs, including afterglows and host galaxies, revealing the richness and progress in this field. The observations of GRBs cover more than 20 orders of magnitude in energy, from 10^-5 eV to 10^15 eV and also in two non-electromagnetic channels, neutrinos and gravitational waves. However the continuation of progress relies on space based instruments to detect and rapidly localise GRBs and distribute the coordinates.
Designing Future Dark Energy Space Missions: II. Photometric Redshift of Space Weak Lensing Optimized Survey
Authors: S. Jouvel, J-P. Kneib, G. Bernstein, O. Ilbert, P. Jelinsky, B. Milliard, A. Ealet, C. Schimd, T. Dahlen, S. Arnouts
arXiv:1003.4294v1
Accurate weak-lensing analysis requires not only accurate measurement of galaxy shapes but also precise and unbiased measurement of galaxy redshifts. The photometric redshift technique appears as the only possibility to determine the redshift of the background galaxies used in the weak-lensing analysis. Using the photometric redshift quality, simple shape measurement requirements, and a proper sky model, we explore what could be an optimal weak-lensing dark energy mission based on FoM calculation. We found that photometric redshifts reach their best accurracy for the bulk of the faint galaxy population when filters have a resolution R~3.2. We show that an optimal mission would survey the sky through 8 filters using 2 cameras (visible and near infrared). Assuming a 5-year mission duration, a mirror size of 1.5m, a 0.5deg2 FOV with a visible pixel scale of 0.15", to maximize the Weak Lensing FoM, an optimal exposure time is found to be 4x200s per filter (at the Galactic poles) thus covering ~11000deg2 of the sky over the mission. This work demonstrates that a full account of the observational strategy is required to properly optimize the instrument parameters to maximize the FoM of the future weak-lensing space dark energy mission.
The Cauchy problem for metric-affine f(R)-gravity in presence of a Klein-Gordon scalar field
Authors: S. Capozziello, S. Vignolo
arXiv:1003.4280v1
We study the initial value formulation of metric-affine f(R)-gravity in presence of a Klein-Gordon scalar field acting as source of the field equations. Sufficient conditions for the well-posedness of the Cauchy problem are formulated. This result completes the analysis of the same problem already considered for other sources.
Tuesday, March 23, 2010
arXiv: 23 Mar 2010
The linear growth rate of structure in Parametrized Post Friedmannian Universes
Authors: Pedro G. Ferreira (Oxford), Constantinos Skordis (Nottingham)
arXiv:1003.4231v1
A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the distribution of galaxies or anisotropies in the Cosmic Microwave Background. It has been argued, however, that it should be possible to constrain a general class of theories of modified gravity by focusing on properties such as the growing mode, gravitational slip and the effective, time varying Newton's constant. We show that assuming certain physical requirements such as stability, metricity and gauge invariance, it is possible to come up with consistency conditions between these various parameters. In this paper we focus on theories which have, at most, 2nd derivatives in the metric variables and find restrictions that shed light on current and future experimental constraints without having to resort to a (as yet unknown) complete theory of modified gravity. We claim that future measurements of the growth of structure on small scales (i.e. from 1-200 h^{-1} Mpc) may lead to tight constraints on both dark energy and modified theories of gravity.
Cosmological parameters from large scale structure - geometric versus shape information
Authors: Jan Hamann, Steen Hannestad, Julien Lesgourgues, Cornelius Rampf, Yvonne Y. Y. Wong
arXiv:1003.3999v1
The matter power spectrum as derived from large scale structure (LSS) surveys contains two important and distinct pieces of information: an overall smooth shape and the imprint of baryon acoustic oscillations (BAO). We investigate the separate impact of these two types of information on cosmological parameter estimation, and show that for the simplest cosmological models, the broad-band shape information currently contained in the SDSS DR7 halo power spectrum (HPS) is by far superseded by geometric information derived from the baryonic features. An immediate corollary is that contrary to popular beliefs, the upper limit on the neutrino mass m_\nu presently derived from LSS combined with cosmic microwave background (CMB) data does not in fact arise from the possible small-scale power suppression due to neutrino free-streaming, if we limit the model framework to minimal LambdaCDM+m_\nu. However, in more complicated models, such as those extended with extra light degrees of freedom and a dark energy equation of state parameter w differing from -1, shape information becomes crucial for the resolution of parameter degeneracies. This conclusion will remain true even when data from the Planck surveyor become available. In the course of our analysis, we introduce a new dewiggling procedure that allows us to extend consistently the use of the SDSS HPS to models with an arbitrary sound horizon at decoupling. All the cases considered here are compatible with the conservative 95%-bounds \sum m_\nu < n_eff =" 4.8">
Evolution of Spherical Overdensity in Thawing Dark energy Models
Authors: N. Chandrachani Devi, Anjan A Sen
arXiv:1003.4094v1
We study the general evolution of spherical overdensities for thawing class of dark energy models. We model dark energy with scalar fields having canonical as well as non-canonical kinetic energy. For non-canonical case, we consider models where the kinetic energy is of the Born-Infeld Form. We consider various potentials like linear, inverse-square, exponential as well as PNGB-type. We also consider that the dark energy virializes together with the matter component inside the spherical overdensity. Our study shows that models with linear potential in particular with Born-Infeld type kinetic term can have siginificant deviations from the $\Lambda$CDM model in terms of density contrast at the time of virialization.
Modified first-order Horava-Lifshitz gravity: Hamiltonian analysis of the general theory and accelerating FRW cosmology in power-law F(R) model
Authors: Sante Carloni, Masud Chaichian, Shin'ichi Nojiri, Sergei D. Odintsov, Markku Oksanen, Anca Tureanu
arXiv:1003.3925v1
We propose the most general modified first-order Ho\v{r}ava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat FRW space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified $F(R)$ Ho\v{r}ava-Lifshitz gravity is introduced. The study of its ultraviolet properties shows that its $z=3$ version seems to be renormalizable in the same way as the original Ho\v{r}ava-Lifshitz proposal. The Hamiltonian analysis of the modified $F(R)$ Ho\v{r}ava-Lifshitz gravity shows that it is in general a consistent theory. The $F(R)$ gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for this $F(R)$ gravity is investigated. It is shown that a special choice of parameters for this theory leads to the same equations of motion as in the case of traditional $F(R)$ gravity. Nevertheless, the cosmological structure of the modified $F(R)$ Ho\v{r}ava-Lifshitz gravity turns out to be much richer than for its traditional counterpart. The emergence of multiple de Sitter solutions indicates to the possibility of unification of early-time inflation with late-time acceleration within the same model. Power-law $F(R)$ theories are also investigated in detail. It is analytically shown that they have a quite rich cosmological structure: early/late-time cosmic acceleration of quintessence, as well as of phantom types. Also it is demonstrated that all the four known types of finite-time future singularities may occur in the power-law Ho\v{r}ava-Lifshitz $F(R)$ gravity. Finally, a covariant proposal for (renormalizable) $F(R)$ gravity within the Ho\v{r}ava-Lifshitz spirit is presented.
On the Origin of Dark Energy
Authors: Arne Bergstrom
arXiv:1003.3870v1
The time-dependent propagation of neutral quanta through space is governed by a rigorous continuity equation (the Boltzmann transport equation). Requiring this equation to take the form of a Lorentz-covariant wave equation implies (i) properties of space-time which an observer would describe as a uniform expansion in agreement with Hubble's law, and (ii) that the quantum transport behaves like in a multiplicative medium with multiplication factor = 2. This inherent, essentially explosive multiplicity of vacuum, caused by the requirement of Lorentz-covariance, is in the paper suggested as a potential origin of dark energy. In addition, it is shown that this requirement of Lorentz-covariant quantum transport leads to an apparent accelerated expansion of the universe in potential agreement with recent astronomical observations.
Emergent Geometry and Gravity from Matrix Models: an Introduction
Authors: Harold Steinacker
arXiv:1003.4134v1
A introductory review to emergent noncommutative gravity within Yang-Mills Matrix models is presented. Space-time is described as a noncommutative brane solution of the matrix model, i.e. as submanifold of \R^D. Fields and matter on the brane arise as fluctuations of the bosonic resp. fermionic matrices around such a background, and couple to an effective metric interpreted in terms of gravity. Suitable tools are provided for the description of the effective geometry in the semi-classical limit. The relation to noncommutative gauge theory and the role of UV/IR mixing is explained. Several types of geometries are identified, in particular "harmonic" and "Einstein" type of solutions. The physics of the harmonic branch is discussed in some detail, emphasizing the non-standard role of vacuum energy. This may provide new approach to some of the big puzzles in this context. The IKKT model with D=10 and close relatives are singled out as promising candidates for a quantum theory of fundamental interactions including gravity.
The unification of gravity with the forces of the standard model on a cosmological scale
Authors: Claus Gerhardt
arXiv:1003.4246v1
We prove the existence of a spectral resolution of the Wheeler-DeWitt equation when the underlying spacetime is a Friedman universe with flat spatial slices and where the matter fields are comprised of the strong interaction, with $\SU(3)$ replaced by a general $\SU(n)$, $n\ge 2$, and the electro-weak interaction. The wave functions are maps from $\R[4n+10]$ to a subspace of the antisymmetric Fock space, and one noteworthy result is that, whenever the electro-weak interaction is involved, the image of an eigenfunction is in general not one dimensional, i.e., in general it makes no sense specifying a fermion and looking for an eigenfunction the range of which is contained in the one dimensional vector space spanned by the fermion.
Authors: Pedro G. Ferreira (Oxford), Constantinos Skordis (Nottingham)
arXiv:1003.4231v1
A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the distribution of galaxies or anisotropies in the Cosmic Microwave Background. It has been argued, however, that it should be possible to constrain a general class of theories of modified gravity by focusing on properties such as the growing mode, gravitational slip and the effective, time varying Newton's constant. We show that assuming certain physical requirements such as stability, metricity and gauge invariance, it is possible to come up with consistency conditions between these various parameters. In this paper we focus on theories which have, at most, 2nd derivatives in the metric variables and find restrictions that shed light on current and future experimental constraints without having to resort to a (as yet unknown) complete theory of modified gravity. We claim that future measurements of the growth of structure on small scales (i.e. from 1-200 h^{-1} Mpc) may lead to tight constraints on both dark energy and modified theories of gravity.
Cosmological parameters from large scale structure - geometric versus shape information
Authors: Jan Hamann, Steen Hannestad, Julien Lesgourgues, Cornelius Rampf, Yvonne Y. Y. Wong
arXiv:1003.3999v1
The matter power spectrum as derived from large scale structure (LSS) surveys contains two important and distinct pieces of information: an overall smooth shape and the imprint of baryon acoustic oscillations (BAO). We investigate the separate impact of these two types of information on cosmological parameter estimation, and show that for the simplest cosmological models, the broad-band shape information currently contained in the SDSS DR7 halo power spectrum (HPS) is by far superseded by geometric information derived from the baryonic features. An immediate corollary is that contrary to popular beliefs, the upper limit on the neutrino mass m_\nu presently derived from LSS combined with cosmic microwave background (CMB) data does not in fact arise from the possible small-scale power suppression due to neutrino free-streaming, if we limit the model framework to minimal LambdaCDM+m_\nu. However, in more complicated models, such as those extended with extra light degrees of freedom and a dark energy equation of state parameter w differing from -1, shape information becomes crucial for the resolution of parameter degeneracies. This conclusion will remain true even when data from the Planck surveyor become available. In the course of our analysis, we introduce a new dewiggling procedure that allows us to extend consistently the use of the SDSS HPS to models with an arbitrary sound horizon at decoupling. All the cases considered here are compatible with the conservative 95%-bounds \sum m_\nu < n_eff =" 4.8">
Evolution of Spherical Overdensity in Thawing Dark energy Models
Authors: N. Chandrachani Devi, Anjan A Sen
arXiv:1003.4094v1
We study the general evolution of spherical overdensities for thawing class of dark energy models. We model dark energy with scalar fields having canonical as well as non-canonical kinetic energy. For non-canonical case, we consider models where the kinetic energy is of the Born-Infeld Form. We consider various potentials like linear, inverse-square, exponential as well as PNGB-type. We also consider that the dark energy virializes together with the matter component inside the spherical overdensity. Our study shows that models with linear potential in particular with Born-Infeld type kinetic term can have siginificant deviations from the $\Lambda$CDM model in terms of density contrast at the time of virialization.
Modified first-order Horava-Lifshitz gravity: Hamiltonian analysis of the general theory and accelerating FRW cosmology in power-law F(R) model
Authors: Sante Carloni, Masud Chaichian, Shin'ichi Nojiri, Sergei D. Odintsov, Markku Oksanen, Anca Tureanu
arXiv:1003.3925v1
We propose the most general modified first-order Ho\v{r}ava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat FRW space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified $F(R)$ Ho\v{r}ava-Lifshitz gravity is introduced. The study of its ultraviolet properties shows that its $z=3$ version seems to be renormalizable in the same way as the original Ho\v{r}ava-Lifshitz proposal. The Hamiltonian analysis of the modified $F(R)$ Ho\v{r}ava-Lifshitz gravity shows that it is in general a consistent theory. The $F(R)$ gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for this $F(R)$ gravity is investigated. It is shown that a special choice of parameters for this theory leads to the same equations of motion as in the case of traditional $F(R)$ gravity. Nevertheless, the cosmological structure of the modified $F(R)$ Ho\v{r}ava-Lifshitz gravity turns out to be much richer than for its traditional counterpart. The emergence of multiple de Sitter solutions indicates to the possibility of unification of early-time inflation with late-time acceleration within the same model. Power-law $F(R)$ theories are also investigated in detail. It is analytically shown that they have a quite rich cosmological structure: early/late-time cosmic acceleration of quintessence, as well as of phantom types. Also it is demonstrated that all the four known types of finite-time future singularities may occur in the power-law Ho\v{r}ava-Lifshitz $F(R)$ gravity. Finally, a covariant proposal for (renormalizable) $F(R)$ gravity within the Ho\v{r}ava-Lifshitz spirit is presented.
On the Origin of Dark Energy
Authors: Arne Bergstrom
arXiv:1003.3870v1
The time-dependent propagation of neutral quanta through space is governed by a rigorous continuity equation (the Boltzmann transport equation). Requiring this equation to take the form of a Lorentz-covariant wave equation implies (i) properties of space-time which an observer would describe as a uniform expansion in agreement with Hubble's law, and (ii) that the quantum transport behaves like in a multiplicative medium with multiplication factor = 2. This inherent, essentially explosive multiplicity of vacuum, caused by the requirement of Lorentz-covariance, is in the paper suggested as a potential origin of dark energy. In addition, it is shown that this requirement of Lorentz-covariant quantum transport leads to an apparent accelerated expansion of the universe in potential agreement with recent astronomical observations.
Emergent Geometry and Gravity from Matrix Models: an Introduction
Authors: Harold Steinacker
arXiv:1003.4134v1
A introductory review to emergent noncommutative gravity within Yang-Mills Matrix models is presented. Space-time is described as a noncommutative brane solution of the matrix model, i.e. as submanifold of \R^D. Fields and matter on the brane arise as fluctuations of the bosonic resp. fermionic matrices around such a background, and couple to an effective metric interpreted in terms of gravity. Suitable tools are provided for the description of the effective geometry in the semi-classical limit. The relation to noncommutative gauge theory and the role of UV/IR mixing is explained. Several types of geometries are identified, in particular "harmonic" and "Einstein" type of solutions. The physics of the harmonic branch is discussed in some detail, emphasizing the non-standard role of vacuum energy. This may provide new approach to some of the big puzzles in this context. The IKKT model with D=10 and close relatives are singled out as promising candidates for a quantum theory of fundamental interactions including gravity.
The unification of gravity with the forces of the standard model on a cosmological scale
Authors: Claus Gerhardt
arXiv:1003.4246v1
We prove the existence of a spectral resolution of the Wheeler-DeWitt equation when the underlying spacetime is a Friedman universe with flat spatial slices and where the matter fields are comprised of the strong interaction, with $\SU(3)$ replaced by a general $\SU(n)$, $n\ge 2$, and the electro-weak interaction. The wave functions are maps from $\R[4n+10]$ to a subspace of the antisymmetric Fock space, and one noteworthy result is that, whenever the electro-weak interaction is involved, the image of an eigenfunction is in general not one dimensional, i.e., in general it makes no sense specifying a fermion and looking for an eigenfunction the range of which is contained in the one dimensional vector space spanned by the fermion.
arXiv: 22 Mar 2010
Dark Energy and Projective Symmetry
Authors: G. W. Gibbons, C. M. Warnick
arXiv:1003.3845v1
Nurowski [arXiv:1003.1503] has recently suggested a link between the observation of Dark Energy in cosmology and the projective equivalence of certain Friedman-Lemaitre-Robertson-Walker (FLRW) metrics. Specifically, he points out that two FLRW metrics with the same unparameterized geodesics have their energy densities differing by a constant. From this he queries whether the existence of dark energy is meaningful. We point out that physical observables in cosmology are not projectively invariant and we relate the projective symmetry uncovered by Nurowski to some previous work on projective equivalence in cosmology.
Magnetic fields and Sunyaev-Zel'dovich effect in galaxy clusters
Authors: Rajesh Gopal, Suparna Roychowdhury
arXiv:1003.3718v1
In this work we study the contribution of magnetic fields to the Sunyaev Zeldovich (SZ) effect in the intracluster medium. In particular we calculate the SZ angular power spectrum and the central temperature decrement. The effect of magnetic fields is included in the hydrostatic equilibrium equation by splitting the Lorentz force into two terms one being the force due to magnetic pressure which acts outwards and the other being magnetic tension which acts inwards. A perturbative approach is adopted to solve for the gas density profile for weak magnetic fields (<> 2000 with sigma_8 ~ 0.8 (WMAP 5 year data) for typical cluster magnetic fields. In addition we also see that the magnetic field effect on the SZ temperature decrement is more pronounced for low mass clusters ( ~ 2 keV). Future SZ detections of low mass clusters at few arc second resolution will be able to probe this effect more precisely. Thus, it will be instructive to explore the implications of this model in greater detail in future works.
Remarks on the consistency of minimal deviations from General Relativity
Authors: Josep M. Pons, Pere Talavera
arXiv:1003.3811v1
We study the consequences of the modification of the phase space structure of General Relativity imposed by breaking the full diffeomorphism invariance but retaining the time foliation preserving diffeomorphisms. We examine the different sectors in phase space that satisfy the new structure of constraints. For some sectors we find an infinite tower of constraints. In spite of that, we also show that these sectors allow for solutions, among them some well known families of black hole and cosmologies which fulfill all the constraints. We raise some physical concerns on the consequences of an absolute Galilean time, on the thermodynamical pathologies of such models and on their unusual vacuum structure.
Authors: G. W. Gibbons, C. M. Warnick
arXiv:1003.3845v1
Nurowski [arXiv:1003.1503] has recently suggested a link between the observation of Dark Energy in cosmology and the projective equivalence of certain Friedman-Lemaitre-Robertson-Walker (FLRW) metrics. Specifically, he points out that two FLRW metrics with the same unparameterized geodesics have their energy densities differing by a constant. From this he queries whether the existence of dark energy is meaningful. We point out that physical observables in cosmology are not projectively invariant and we relate the projective symmetry uncovered by Nurowski to some previous work on projective equivalence in cosmology.
Magnetic fields and Sunyaev-Zel'dovich effect in galaxy clusters
Authors: Rajesh Gopal, Suparna Roychowdhury
arXiv:1003.3718v1
In this work we study the contribution of magnetic fields to the Sunyaev Zeldovich (SZ) effect in the intracluster medium. In particular we calculate the SZ angular power spectrum and the central temperature decrement. The effect of magnetic fields is included in the hydrostatic equilibrium equation by splitting the Lorentz force into two terms one being the force due to magnetic pressure which acts outwards and the other being magnetic tension which acts inwards. A perturbative approach is adopted to solve for the gas density profile for weak magnetic fields (<> 2000 with sigma_8 ~ 0.8 (WMAP 5 year data) for typical cluster magnetic fields. In addition we also see that the magnetic field effect on the SZ temperature decrement is more pronounced for low mass clusters (
Remarks on the consistency of minimal deviations from General Relativity
Authors: Josep M. Pons, Pere Talavera
arXiv:1003.3811v1
We study the consequences of the modification of the phase space structure of General Relativity imposed by breaking the full diffeomorphism invariance but retaining the time foliation preserving diffeomorphisms. We examine the different sectors in phase space that satisfy the new structure of constraints. For some sectors we find an infinite tower of constraints. In spite of that, we also show that these sectors allow for solutions, among them some well known families of black hole and cosmologies which fulfill all the constraints. We raise some physical concerns on the consequences of an absolute Galilean time, on the thermodynamical pathologies of such models and on their unusual vacuum structure.
arXiv: 19 Mar 2010
Light elements in stars with exoplanets
Authors: N.C. Santos, E. Delgado Mena, G. Israelian, J. I. González-Hernández, M. C. Gálvez-Ortiz, M. Mayor, S. Udry, R. Rebolo, S. Sousa, S. Randich
arXiv:1003.3544v1
It is well known that stars orbited by giant planets have higher abundances of heavy elements when compared with average field dwarfs. A number of studies have also addressed the possibility that light element abundances are different in these stars. In this paper we will review the present status of these studies. The most significant trends will be discussed.
Local Group Dwarf Spheroidals: Correlated Deviations from the Baryonic Tully-Fisher Relation
Authors: Stacy S. McGaugh, Joe Wolf
arXiv:1003.3448v1
Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption. Fainter, more elliptical, and tidally more susceptible dwarfs deviate further from the BTFR. We consider a variety of mechanisms that might lead to this behavior. Reionization does not, by itself, suffice to explain all aspects of the data. Further mechanisms such as supernova feedback or ram pressure stripping may remove gas that would otherwise be present to satisfy the baryonic mass budget. The correlation with ellipticity and tidal susceptibility implies that the usual assumption of spherical systems in stable equilibria may not hold, and suggests an alternate (or additional) mechanism by which baryons are lost through tidal stripping. In this case, we predict the mass of streams that should be associated with each dwarf in order to restore consistency with the BTFR. Finally, we consider an alternative to dark matter, MOND. The mass-to-light ratios of the dwarfs which adhere to the BTFR are reasonable, but those which deviate are not: the mass-to-light ratios of the ultrafaint dwarfs are far too high to be explained by MOND. This would falsify the theory if these objects are stable, bound systems. However, the dwarfs are considerably more susceptible to tidal effects in MOND than with dark matter. The deviation sets in where the observed radii of the dwarfs exceed the MONDian tidal radii. The extent to which the dwarfs are currently being tidally stripped therefore becomes a powerful test of the MOND hypothesis.
Authors: N.C. Santos, E. Delgado Mena, G. Israelian, J. I. González-Hernández, M. C. Gálvez-Ortiz, M. Mayor, S. Udry, R. Rebolo, S. Sousa, S. Randich
arXiv:1003.3544v1
It is well known that stars orbited by giant planets have higher abundances of heavy elements when compared with average field dwarfs. A number of studies have also addressed the possibility that light element abundances are different in these stars. In this paper we will review the present status of these studies. The most significant trends will be discussed.
Local Group Dwarf Spheroidals: Correlated Deviations from the Baryonic Tully-Fisher Relation
Authors: Stacy S. McGaugh, Joe Wolf
arXiv:1003.3448v1
Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption. Fainter, more elliptical, and tidally more susceptible dwarfs deviate further from the BTFR. We consider a variety of mechanisms that might lead to this behavior. Reionization does not, by itself, suffice to explain all aspects of the data. Further mechanisms such as supernova feedback or ram pressure stripping may remove gas that would otherwise be present to satisfy the baryonic mass budget. The correlation with ellipticity and tidal susceptibility implies that the usual assumption of spherical systems in stable equilibria may not hold, and suggests an alternate (or additional) mechanism by which baryons are lost through tidal stripping. In this case, we predict the mass of streams that should be associated with each dwarf in order to restore consistency with the BTFR. Finally, we consider an alternative to dark matter, MOND. The mass-to-light ratios of the dwarfs which adhere to the BTFR are reasonable, but those which deviate are not: the mass-to-light ratios of the ultrafaint dwarfs are far too high to be explained by MOND. This would falsify the theory if these objects are stable, bound systems. However, the dwarfs are considerably more susceptible to tidal effects in MOND than with dark matter. The deviation sets in where the observed radii of the dwarfs exceed the MONDian tidal radii. The extent to which the dwarfs are currently being tidally stripped therefore becomes a powerful test of the MOND hypothesis.
arXiv: 18 Mar 2010
A geometrical approach to nonlinear perturbations in relativistic cosmology
Authors: David Langlois, Filippo Vernizzi
arXiv:1003.3270v1
We give a pedagogical review of a covariant and fully non-perturbative approach to study nonlinear perturbations in cosmology. In the first part, devoted to cosmological fluids, we define a nonlinear extension of the uniform-density curvature perturbation and derive its evolution equation. In the second part, we focus our attention on multiple scalar fields and present a nonlinear description in terms of adiabatic and entropy perturbations. In both cases, we show how the formalism presented here enables one to easily obtain equations up to second, third and higher orders.
Authors: David Langlois, Filippo Vernizzi
arXiv:1003.3270v1
We give a pedagogical review of a covariant and fully non-perturbative approach to study nonlinear perturbations in cosmology. In the first part, devoted to cosmological fluids, we define a nonlinear extension of the uniform-density curvature perturbation and derive its evolution equation. In the second part, we focus our attention on multiple scalar fields and present a nonlinear description in terms of adiabatic and entropy perturbations. In both cases, we show how the formalism presented here enables one to easily obtain equations up to second, third and higher orders.
arXiv: 17 Mar 2010
Constraints on Perturbative f(R) Gravity via Neutron Stars
Authors: A. Savas Arapoglu, Cemsinan Deliduman, K. Yavuz Eksi
arXiv:1003.3179v2
We study the structure of neutron stars in perturbative f(R) gravity models with realistic equations of state. We obtain the mass-radius relation in gravity models of the form f(R)=R+\alpha R^2 and f(R)=R+\beta R^3. Using the recent observational constraints on the mass-radius relation, we find that \alpha \lesssim 10^{10} cm^{2} and \beta \lesssim 10^{21} cm^{4}. This implies, for such gravity models, that deviations from Einstein's general relativity in the strong gravity regime should be within a curvature scale of 10^{-10} cm^{-2}.
Wiggles in the cosmic microwave background radiation: echoes from non-singular cyclic-inflation
Authors: Tirthabir Biswas, Anupam Mazumdar, Arman Shafieloo
arXiv:1003.3206v1
In this paper we consider a unique model of inflation where the universe undergoes rapid asymmetric oscillations, each cycle lasting millions of Planck time. Over many-many cycles the space-time expands to mimic the standard inflationary scenario. Moreover, these rapid oscillations leave a distinctive periodic signature in ln(k) in the primordial power spectrum, where k denotes the comoving scale. The best fit parameters of the cyclic-inflation model provides a very good fit to the 7-year WMAP data.
Cosmological backreaction
Authors: Dominik J. Schwarz
arXiv:1003.3026v1
This work summarises some of the attempts to explain the phenomenon of dark energy as an effective description of complex gravitational physics and the proper interpretation of observations. Cosmological backreaction has been shown to be relevant for observational (precision) cosmology, nevertheless no convincing explanation of dark energy by means of backreaction has been given so far.
Authors: A. Savas Arapoglu, Cemsinan Deliduman, K. Yavuz Eksi
arXiv:1003.3179v2
We study the structure of neutron stars in perturbative f(R) gravity models with realistic equations of state. We obtain the mass-radius relation in gravity models of the form f(R)=R+\alpha R^2 and f(R)=R+\beta R^3. Using the recent observational constraints on the mass-radius relation, we find that \alpha \lesssim 10^{10} cm^{2} and \beta \lesssim 10^{21} cm^{4}. This implies, for such gravity models, that deviations from Einstein's general relativity in the strong gravity regime should be within a curvature scale of 10^{-10} cm^{-2}.
Wiggles in the cosmic microwave background radiation: echoes from non-singular cyclic-inflation
Authors: Tirthabir Biswas, Anupam Mazumdar, Arman Shafieloo
arXiv:1003.3206v1
In this paper we consider a unique model of inflation where the universe undergoes rapid asymmetric oscillations, each cycle lasting millions of Planck time. Over many-many cycles the space-time expands to mimic the standard inflationary scenario. Moreover, these rapid oscillations leave a distinctive periodic signature in ln(k) in the primordial power spectrum, where k denotes the comoving scale. The best fit parameters of the cyclic-inflation model provides a very good fit to the 7-year WMAP data.
Cosmological backreaction
Authors: Dominik J. Schwarz
arXiv:1003.3026v1
This work summarises some of the attempts to explain the phenomenon of dark energy as an effective description of complex gravitational physics and the proper interpretation of observations. Cosmological backreaction has been shown to be relevant for observational (precision) cosmology, nevertheless no convincing explanation of dark energy by means of backreaction has been given so far.
Tuesday, March 16, 2010
arXiv: 16 Mar 2010
Constraints on f(R) gravity from probing the large-scale structure
Authors: Lucas Lombriser, Anze Slosar, Uros Seljak, Wayne Hu
arXiv:1003.3009v1
We study cosmological constraints on metric f(R) gravity models that are designed to reproduce the LCDM expansion history with modifications to gravity described by a supplementary cosmological freedom, the Compton wavelength parameter B_0. We conduct a Markov chain Monte Carlo analysis on the parameter space, utilizing the geometrical constraints from supernovae distances, the baryon acoustic oscillations distances, and the Hubble constant, along with all of the cosmic microwave background data, including the largest scales, its correlation with galaxies, and a probe of the relation between weak gravitational lensing and galaxy flows. The strongest constraints, however, are obtained through the inclusion of data from cluster abundance. Using all of the data, we infer a bound of B_0<0.0011>
Exploring extra dimensions through observational tests of dark energy and varying Newton's constant
Authors: Paul J. Steinhardt, Daniel Wesley
arXiv:1003.2815v1
We recently presented a series of dark energy theorems that place constraints on the equation of state of dark energy ($\wdark$), the ime-variation of Newton's constant ($\dot G$), and the violation of energy conditions in theories with extra dimensions. In this paper, we explore how current and future measurements of $\wdark$ and $\dot G$ can be used to place tight limits on large classes of these theories (including some of the most well-motivated examples) independent of the size of the extra dimensions. As an example, we show that models with conformally Ricci-flat metrics obeying the null energy condition (a common ansatz for Kaluza-Klein and string constructions) are highly constrained by current ata and may be ruled out entirely by future dark energy and pulsar observations.
A New Type of Dark Energy Model
Authors: Yi Zhang, Hui Li
arXiv:1003.2788v1
In this paper, we propose a general form of the equation of state (EoS) which is the function of the fractional dark energy density $\Omega_{d}$. At least, five related models, the cosmological constant model, the holographic dark energy model, the agegraphic dark energy model, the modified holographic dark energy model and the Ricci scalar holographic dark energy model are included in this form. Furthermore, if we consider proper interactions, the interactive variants of those models can be included as well. The phase-space analysis shows that the scaling solutions may exist both in the non-interacting and interacting cases. And the stability analysis of the system could give out the attractor solution which could alleviate the coincidence problem.
Cosmological Condensation of Scalar Fields -- Making a dark energy
Authors: Houri Ziaeepour
arXiv:1003.2996v1
Our Universe is ruled by quantum mechanics and its extension Quantum Field Theory (QFT). However, the explanations for a number of cosmological phenomena such as inflation, dark energy, symmetry breakings, and phase transitions need the presence of classical scalar fields. Although the process of condensation of scalar fields in the lab is fairly well understood, the extension of results to a cosmological context is not trivial. Here we investigate the formation of a condensate - a classical scalar field - after reheating of the Universe. We assume a light quantum scalar field produced by the decay of a heavy particle, which for simplicity is assumed to be another scalar. We show that during radiation domination epoch under certain conditions, the decay of the heavy particle alone is sufficient for the production of a condensate. This process is very similar to preheating - the exponential particle production at the end of inflation. During matter domination epoch when the expansion of the Universe is faster, the decay alone can not keep the growing trend of the field and the amplitude of the condensate decreases rapidly, unless there is a self interaction. This issue is particularly important for dark energy. We show that quantum corrections of the self-interaction play a crucial role in this process. Notably, they induce an effective action which includes inverse power-law terms, and therefore can lead to a tracking behaviour even when the classical self-interaction is a simple power-law of order 3 or 4. This removes the necessity of having nonrenormalisable terms in the Lagrangian. If dark energy is the condensate of a quantum scalar field, these results show that its presence is deeply related to the action of quantum physics at largest observable scales.
On Semi-classical Degravitation and the Cosmological Constant Problems
Authors: Subodh P. Patil
arXiv:1003.3010v1
In this report, we discuss a candidate mechanism through which one might address the various cosmological constant problems. We first observe that the renormalization of gravitational couplings (induced by integrating out various matter fields) manifests non-local modifications to Einstein's equations as quantum corrected equations of motion. That is, at the loop level, matter sources curvature through a gravitational coupling that is a non-local function of the covariant d'Alembertian. If the functional form of the resulting Newton's `constant' is such that it annihilates very long wavelength sources, but reduces to $1/M^2_{pl}$ ($M_{pl}$ being the 4d Planck mass) for all sources with cosmologically observable wavelengths, we would have a complimentary realization of the degravitation paradigm-- a realization through which its non-linear completion and the corresponding modified Bianchi identities are readily understood. We proceed to consider various theories whose coupling to gravity may a priori induce non-trivial renormalizations of Newton's constant in the IR, and arrive at a class of non-local effective actions which yield a suitably degravitating filter function for Newton's constant upon subsequently being integrated out. We motivate this class of non-local theories through several considerations, discuss open issues, future directions, the inevitable question of scheme dependence in semi-classical gravitational calculations and comment on connections with other meditations in the literature on relaxing of the cosmological constant semi-classically.
On the Orbit of Exoplanet WASP-12b
Authors: Christopher J. Campo, Joseph Harrington, Ryan A. Hardy, Kevin B. Stevenson, Sarah Nymeyer, Darin Ragozzine, Nate B. Lust, David R. Anderson, Andrew Collier-Cameron, Jasmina Blecic, Christopher B. T. Britt, William C. Bowman, Peter J. Wheatley, Drake Deming, Leslie Hebb, Coel Hellier, Pierre F. L. Maxted, Don Pollaco, Richard G. West
arXiv:1003.2763v1
We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity. The ground-based secondary eclipse phase reported by Lopez-Morales et al. (0.510 +/- 0.002) implies eccentricity at the 4.5\sigma level, and the spectroscopic orbit of Hebb et al. has eccentricity 0.049 +/- 0.015, a 3\sigma result, and predicts an eclipse phase of 0.509 +/- 0.007. Our eclipse phases are 0.5012 +/- 0.0006 (3.6 and 5.8 micron) and 0.5007 +/- 0.0007 (4.5 and 8.0 micron). These values are inconsistent with the ground-based data, but marginally consistent with the spectroscopic orbit. Considering the unlikely possibility that precession brought the long axis of the orbit into alignment during our observations, a model considering these points and transit times from professional and amateur observers estimates orbital precession at \omega = 0.02 +/- 0.01 deg/d. This implies a tidal Love number, k2p, of 0.15 +/- 0.08, indicating a very centrally condensed planet. However, if the orbit is actually eccentric, we have observed it at a remarkably special time to find eclipse phases consistent with apsidal alignment. Future observations can decide between these possibilities
Authors: Lucas Lombriser, Anze Slosar, Uros Seljak, Wayne Hu
arXiv:1003.3009v1
We study cosmological constraints on metric f(R) gravity models that are designed to reproduce the LCDM expansion history with modifications to gravity described by a supplementary cosmological freedom, the Compton wavelength parameter B_0. We conduct a Markov chain Monte Carlo analysis on the parameter space, utilizing the geometrical constraints from supernovae distances, the baryon acoustic oscillations distances, and the Hubble constant, along with all of the cosmic microwave background data, including the largest scales, its correlation with galaxies, and a probe of the relation between weak gravitational lensing and galaxy flows. The strongest constraints, however, are obtained through the inclusion of data from cluster abundance. Using all of the data, we infer a bound of B_0<0.0011>
Exploring extra dimensions through observational tests of dark energy and varying Newton's constant
Authors: Paul J. Steinhardt, Daniel Wesley
arXiv:1003.2815v1
We recently presented a series of dark energy theorems that place constraints on the equation of state of dark energy ($\wdark$), the ime-variation of Newton's constant ($\dot G$), and the violation of energy conditions in theories with extra dimensions. In this paper, we explore how current and future measurements of $\wdark$ and $\dot G$ can be used to place tight limits on large classes of these theories (including some of the most well-motivated examples) independent of the size of the extra dimensions. As an example, we show that models with conformally Ricci-flat metrics obeying the null energy condition (a common ansatz for Kaluza-Klein and string constructions) are highly constrained by current ata and may be ruled out entirely by future dark energy and pulsar observations.
A New Type of Dark Energy Model
Authors: Yi Zhang, Hui Li
arXiv:1003.2788v1
In this paper, we propose a general form of the equation of state (EoS) which is the function of the fractional dark energy density $\Omega_{d}$. At least, five related models, the cosmological constant model, the holographic dark energy model, the agegraphic dark energy model, the modified holographic dark energy model and the Ricci scalar holographic dark energy model are included in this form. Furthermore, if we consider proper interactions, the interactive variants of those models can be included as well. The phase-space analysis shows that the scaling solutions may exist both in the non-interacting and interacting cases. And the stability analysis of the system could give out the attractor solution which could alleviate the coincidence problem.
Cosmological Condensation of Scalar Fields -- Making a dark energy
Authors: Houri Ziaeepour
arXiv:1003.2996v1
Our Universe is ruled by quantum mechanics and its extension Quantum Field Theory (QFT). However, the explanations for a number of cosmological phenomena such as inflation, dark energy, symmetry breakings, and phase transitions need the presence of classical scalar fields. Although the process of condensation of scalar fields in the lab is fairly well understood, the extension of results to a cosmological context is not trivial. Here we investigate the formation of a condensate - a classical scalar field - after reheating of the Universe. We assume a light quantum scalar field produced by the decay of a heavy particle, which for simplicity is assumed to be another scalar. We show that during radiation domination epoch under certain conditions, the decay of the heavy particle alone is sufficient for the production of a condensate. This process is very similar to preheating - the exponential particle production at the end of inflation. During matter domination epoch when the expansion of the Universe is faster, the decay alone can not keep the growing trend of the field and the amplitude of the condensate decreases rapidly, unless there is a self interaction. This issue is particularly important for dark energy. We show that quantum corrections of the self-interaction play a crucial role in this process. Notably, they induce an effective action which includes inverse power-law terms, and therefore can lead to a tracking behaviour even when the classical self-interaction is a simple power-law of order 3 or 4. This removes the necessity of having nonrenormalisable terms in the Lagrangian. If dark energy is the condensate of a quantum scalar field, these results show that its presence is deeply related to the action of quantum physics at largest observable scales.
On Semi-classical Degravitation and the Cosmological Constant Problems
Authors: Subodh P. Patil
arXiv:1003.3010v1
In this report, we discuss a candidate mechanism through which one might address the various cosmological constant problems. We first observe that the renormalization of gravitational couplings (induced by integrating out various matter fields) manifests non-local modifications to Einstein's equations as quantum corrected equations of motion. That is, at the loop level, matter sources curvature through a gravitational coupling that is a non-local function of the covariant d'Alembertian. If the functional form of the resulting Newton's `constant' is such that it annihilates very long wavelength sources, but reduces to $1/M^2_{pl}$ ($M_{pl}$ being the 4d Planck mass) for all sources with cosmologically observable wavelengths, we would have a complimentary realization of the degravitation paradigm-- a realization through which its non-linear completion and the corresponding modified Bianchi identities are readily understood. We proceed to consider various theories whose coupling to gravity may a priori induce non-trivial renormalizations of Newton's constant in the IR, and arrive at a class of non-local effective actions which yield a suitably degravitating filter function for Newton's constant upon subsequently being integrated out. We motivate this class of non-local theories through several considerations, discuss open issues, future directions, the inevitable question of scheme dependence in semi-classical gravitational calculations and comment on connections with other meditations in the literature on relaxing of the cosmological constant semi-classically.
On the Orbit of Exoplanet WASP-12b
Authors: Christopher J. Campo, Joseph Harrington, Ryan A. Hardy, Kevin B. Stevenson, Sarah Nymeyer, Darin Ragozzine, Nate B. Lust, David R. Anderson, Andrew Collier-Cameron, Jasmina Blecic, Christopher B. T. Britt, William C. Bowman, Peter J. Wheatley, Drake Deming, Leslie Hebb, Coel Hellier, Pierre F. L. Maxted, Don Pollaco, Richard G. West
arXiv:1003.2763v1
We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity. The ground-based secondary eclipse phase reported by Lopez-Morales et al. (0.510 +/- 0.002) implies eccentricity at the 4.5\sigma level, and the spectroscopic orbit of Hebb et al. has eccentricity 0.049 +/- 0.015, a 3\sigma result, and predicts an eclipse phase of 0.509 +/- 0.007. Our eclipse phases are 0.5012 +/- 0.0006 (3.6 and 5.8 micron) and 0.5007 +/- 0.0007 (4.5 and 8.0 micron). These values are inconsistent with the ground-based data, but marginally consistent with the spectroscopic orbit. Considering the unlikely possibility that precession brought the long axis of the orbit into alignment during our observations, a model considering these points and transit times from professional and amateur observers estimates orbital precession at \omega = 0.02 +/- 0.01 deg/d. This implies a tidal Love number, k2p, of 0.15 +/- 0.08, indicating a very centrally condensed planet. However, if the orbit is actually eccentric, we have observed it at a remarkably special time to find eclipse phases consistent with apsidal alignment. Future observations can decide between these possibilities
arXiv: 15 Mar 2010
Breaking the sigma_8-Omega_m degeneracy using the clustering of high-z X-ray AGN
Authors: S.Basilakos (Academy of Athens, Greece), M.Plionis (National Obs. of Athens, Greece and INAOE-Mexico)
arXiv:1003.2559v1
The clustering of X-ray selected AGN appears to be a valuable tool for extracting cosmological information. Using the recent high-precision angular clustering results of ~30000 XMM-Newton soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009), which have a median redshift of $z\sim 1$, and assuming a flat geometry, a constant in comoving coordinates AGN clustering evolution and the AGN bias evolution model of Basilakos et al. (2008), we manage to break the Omega_m-sigma_8 degeneracy. The resulting cosmological constraints are: Omega_m=0.27 (+0.03 -0.05), w=-0.90 (+0.10 -0.16) and sigma_8=0.74 (+0.14 -0.12), while the dark matter host halo mass, in which the X-ray selected AGN are presumed to reside, is M=2.50 (+0.50 -1.50) X 10^13 h^{-1} M(solar). For the constant Lambda model (w=-1) we find Omega_m=0.24 (+- 0.06) and sigma_8=0.83 (+0.11 -0.16), in good agreement with recent studies based on cluster abundances, weak lensing and the CMB, but in disagreement with the recent bulk flow analysis.
Decomposition of Spectra from Redshift Distortion Maps
Authors: Yong-Seon Song, Issha Kayo
arXiv:1003.2420v1
We develop an optimized technique to extract density--density and velocity--velocity spectra out of observed spectra in redshift space. The measured spectra of the distribution of halos from redshift distorted mock map are binned into 2--dimensional coordinates in Fourier space so as to be decomposed into both spectra using angular projection dependence. With the threshold limit introduced to minimize nonlinear suppression, the decomposed velocity--velocity spectra are reasonably well measured up to scale k=0.07 h/Mpc, and the measured variances using our method are consistent with errors predicted from a Fisher matrix analysis. The detectability is extendable to k\sim 0.1 h/Mpc with more conservative bounds at the cost of weakened constraint.
Transit Timing Variations for Inclined and Retrograde Exoplanetary Systems
Authors: Matthew J. Payne, Eric B. Ford, Dimitri Veras
arXiv:1003.2418v1
We perform numerical calculations of the expected transit timing variations (TTVs) induced on a Hot-Jupiter by an Earth-mass perturber. Motivated by the recent discoveries of retrograde transiting planets, we concentrate on an investigation of the effect of varying relative planetary inclinations, up to and including completely retrograde systems. We find that planets in low order (E.g. 2:1) mean-motion resonances (MMRs) retain approximately constant TTV amplitudes for $0<\,^{\circ}i<170\,^{\circ}$,> 170\,^{\circ}$. Systems in higher order MMRs (E.g. 5:1) increase in TTV amplitude as inclinations increase towards $45\,^{\circ}$, becoming approximately constant for $45 <> 135\,^{\circ}$. Planets away from resonance slowly decrease in TTV amplitude as inclinations increase from 0 to 180, where-as planets adjacent to resonances can exhibit a huge range of variability in TTV amplitude as a function of both eccentricity and inclination. For highly retrograde systems ($135\,^{\circ} <>
Authors: S.Basilakos (Academy of Athens, Greece), M.Plionis (National Obs. of Athens, Greece and INAOE-Mexico)
arXiv:1003.2559v1
The clustering of X-ray selected AGN appears to be a valuable tool for extracting cosmological information. Using the recent high-precision angular clustering results of ~30000 XMM-Newton soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009), which have a median redshift of $z\sim 1$, and assuming a flat geometry, a constant in comoving coordinates AGN clustering evolution and the AGN bias evolution model of Basilakos et al. (2008), we manage to break the Omega_m-sigma_8 degeneracy. The resulting cosmological constraints are: Omega_m=0.27 (+0.03 -0.05), w=-0.90 (+0.10 -0.16) and sigma_8=0.74 (+0.14 -0.12), while the dark matter host halo mass, in which the X-ray selected AGN are presumed to reside, is M=2.50 (+0.50 -1.50) X 10^13 h^{-1} M(solar). For the constant Lambda model (w=-1) we find Omega_m=0.24 (+- 0.06) and sigma_8=0.83 (+0.11 -0.16), in good agreement with recent studies based on cluster abundances, weak lensing and the CMB, but in disagreement with the recent bulk flow analysis.
Decomposition of Spectra from Redshift Distortion Maps
Authors: Yong-Seon Song, Issha Kayo
arXiv:1003.2420v1
We develop an optimized technique to extract density--density and velocity--velocity spectra out of observed spectra in redshift space. The measured spectra of the distribution of halos from redshift distorted mock map are binned into 2--dimensional coordinates in Fourier space so as to be decomposed into both spectra using angular projection dependence. With the threshold limit introduced to minimize nonlinear suppression, the decomposed velocity--velocity spectra are reasonably well measured up to scale k=0.07 h/Mpc, and the measured variances using our method are consistent with errors predicted from a Fisher matrix analysis. The detectability is extendable to k\sim 0.1 h/Mpc with more conservative bounds at the cost of weakened constraint.
Transit Timing Variations for Inclined and Retrograde Exoplanetary Systems
Authors: Matthew J. Payne, Eric B. Ford, Dimitri Veras
arXiv:1003.2418v1
We perform numerical calculations of the expected transit timing variations (TTVs) induced on a Hot-Jupiter by an Earth-mass perturber. Motivated by the recent discoveries of retrograde transiting planets, we concentrate on an investigation of the effect of varying relative planetary inclinations, up to and including completely retrograde systems. We find that planets in low order (E.g. 2:1) mean-motion resonances (MMRs) retain approximately constant TTV amplitudes for $0<\,^{\circ}i<170\,^{\circ}$,> 170\,^{\circ}$. Systems in higher order MMRs (E.g. 5:1) increase in TTV amplitude as inclinations increase towards $45\,^{\circ}$, becoming approximately constant for $45 <> 135\,^{\circ}$. Planets away from resonance slowly decrease in TTV amplitude as inclinations increase from 0 to 180, where-as planets adjacent to resonances can exhibit a huge range of variability in TTV amplitude as a function of both eccentricity and inclination. For highly retrograde systems ($135\,^{\circ} <>
Friday, March 12, 2010
arXiv: 12 Mar 2010
A Unified Approach to Cosmic Acceleration
Authors: Minjoon Park, Scott Watson, Kathryn M. Zurek
arXiv:1003.1722v1
We present a unified framework for the study of late time cosmic acceleration. Using methods of effective field theory, we show that existing proposals for late time acceleration can be subsumed in a single framework, rather than many compartmentalized theories. We construct the most general action consistent with symmetry principles, derive the back- ground and perturbation evolution equations, and demonstrate that for special choices of our parameters we can reproduce results already existing in the literature. Lastly, we lay the foundation for future work placing phenomenological constraints on the parameters of the effective theory. Although in this paper we focus on late time acceleration, our construction also generalizes the effective field theory of inflation to the scalar-tensor and multi-field case.
Correlations between 21 cm Radiation and the CMB from Active Sources
Authors: Aaron Berndsen, Levon Pogosian, Mark Wyman
arXiv:1003.2214v1
Neutral hydrogen is ubiquitous, absorbing and emitting 21 cm radiation throughout much of the Universe's history. Active sources of perturbations, such as cosmic strings, would generate simultaneous perturbations in the distribution of neutral hydrogen and in the Cosmic Microwave Background (CMB) radiation from recombination. Moving strings would create wakes leading to 21 cm brightness fluctuations, while also perturbing CMB light via the Gott-Kaiser-Stebbins effect. This would lead to spatial correlations between the 21 cm and CMB anisotropies. Passive sources, like inflationary perturbations, predict no cross correlations prior to the onset of reionization. Thus, observation of any cross correlation between CMB and 21 cm radiation from dark ages would constitute evidence for new physics. We calculate the cosmic string induced correlations between CMB and 21 cm and evaluate their observability.
Shapes of Gas, Gravitational Potential and Dark Matter in Lambda-CDM Clusters
Authors: Erwin T. Lau, Daisuke Nagai, Andrey V. Kravtsov, Andrew R. Zentner
arXiv:1003.2270v1
We present analysis of the three-dimensional shape of intracluster gas in clusters formed in cosmological simulations of the Lambda-CDM cosmology and compare it to the shape of dark matter distribution and the shape of the overall iso-potential surfaces. We find that in simulations with radiative cooling, star formation and stellar feedback (CSF), intracluster gas outside the cluster core is more spherical compared to non-radiative (NR) simulations, while in the core the gas in the CSF runs is more triaxial and has a distinctly oblate shape. The latter reflects the ongoing cooling of gas, which settles into a thick oblate ellipsoid as it loses thermal energy. The shape of the gas in the inner regions of clusters can therefore be a useful diagnostic of gas cooling. We find that gas traces the shape of the underlying potential rather well outside the core, as expected in hydrostatic equilibrium. At smaller radii, however, the gas and potential shapes differ significantly. In the CSF runs, the difference reflects the fact that gas is partly rotationally supported. Interestingly, we find that in non-radiative simulations the difference between gas and potential shape at small radii is due to random gas motions, which make the gas distribution more spherical than the equi-potential surfaces. Finally, we use mock Chandra X-ray maps to show that the differences in shapes observed in three-dimensional distribution of gas are discernible in the ellipticity of X-ray isophotes. Contrasting the ellipticities measured in simulated clusters against observations can therefore constrain the amount of cooling of the intracluster medium and the presence of random gas motions in cluster cores.
Holographic Dark Energy: its Observational Constraints and Theoretical Features
Authors: Yin-Zhe Ma
arXiv:1003.2415v1
We investigate the observational signatures of the holographic dark energy model in this paper, including both the original model and a model with an interaction term between the dark energy and dark matter. We first delineate the dynamical behavior of such models, especially whether they would have a "Big Rip" for different parameters, then we use several recent observational data to give more reliable and tighter constraints on the models. The results favor the equation of state of dark energy crossing -1, and the universe ends in the "Big Rip" phase. By using the Bayesian evidence as a model selection criterion to make the model comparison, we find that the holographic dark energy models are mildly favored by the observations compared with the $% \mathrm{\Lambda CDM}$ model.
Authors: Minjoon Park, Scott Watson, Kathryn M. Zurek
arXiv:1003.1722v1
We present a unified framework for the study of late time cosmic acceleration. Using methods of effective field theory, we show that existing proposals for late time acceleration can be subsumed in a single framework, rather than many compartmentalized theories. We construct the most general action consistent with symmetry principles, derive the back- ground and perturbation evolution equations, and demonstrate that for special choices of our parameters we can reproduce results already existing in the literature. Lastly, we lay the foundation for future work placing phenomenological constraints on the parameters of the effective theory. Although in this paper we focus on late time acceleration, our construction also generalizes the effective field theory of inflation to the scalar-tensor and multi-field case.
Correlations between 21 cm Radiation and the CMB from Active Sources
Authors: Aaron Berndsen, Levon Pogosian, Mark Wyman
arXiv:1003.2214v1
Neutral hydrogen is ubiquitous, absorbing and emitting 21 cm radiation throughout much of the Universe's history. Active sources of perturbations, such as cosmic strings, would generate simultaneous perturbations in the distribution of neutral hydrogen and in the Cosmic Microwave Background (CMB) radiation from recombination. Moving strings would create wakes leading to 21 cm brightness fluctuations, while also perturbing CMB light via the Gott-Kaiser-Stebbins effect. This would lead to spatial correlations between the 21 cm and CMB anisotropies. Passive sources, like inflationary perturbations, predict no cross correlations prior to the onset of reionization. Thus, observation of any cross correlation between CMB and 21 cm radiation from dark ages would constitute evidence for new physics. We calculate the cosmic string induced correlations between CMB and 21 cm and evaluate their observability.
Shapes of Gas, Gravitational Potential and Dark Matter in Lambda-CDM Clusters
Authors: Erwin T. Lau, Daisuke Nagai, Andrey V. Kravtsov, Andrew R. Zentner
arXiv:1003.2270v1
We present analysis of the three-dimensional shape of intracluster gas in clusters formed in cosmological simulations of the Lambda-CDM cosmology and compare it to the shape of dark matter distribution and the shape of the overall iso-potential surfaces. We find that in simulations with radiative cooling, star formation and stellar feedback (CSF), intracluster gas outside the cluster core is more spherical compared to non-radiative (NR) simulations, while in the core the gas in the CSF runs is more triaxial and has a distinctly oblate shape. The latter reflects the ongoing cooling of gas, which settles into a thick oblate ellipsoid as it loses thermal energy. The shape of the gas in the inner regions of clusters can therefore be a useful diagnostic of gas cooling. We find that gas traces the shape of the underlying potential rather well outside the core, as expected in hydrostatic equilibrium. At smaller radii, however, the gas and potential shapes differ significantly. In the CSF runs, the difference reflects the fact that gas is partly rotationally supported. Interestingly, we find that in non-radiative simulations the difference between gas and potential shape at small radii is due to random gas motions, which make the gas distribution more spherical than the equi-potential surfaces. Finally, we use mock Chandra X-ray maps to show that the differences in shapes observed in three-dimensional distribution of gas are discernible in the ellipticity of X-ray isophotes. Contrasting the ellipticities measured in simulated clusters against observations can therefore constrain the amount of cooling of the intracluster medium and the presence of random gas motions in cluster cores.
Holographic Dark Energy: its Observational Constraints and Theoretical Features
Authors: Yin-Zhe Ma
arXiv:1003.2415v1
We investigate the observational signatures of the holographic dark energy model in this paper, including both the original model and a model with an interaction term between the dark energy and dark matter. We first delineate the dynamical behavior of such models, especially whether they would have a "Big Rip" for different parameters, then we use several recent observational data to give more reliable and tighter constraints on the models. The results favor the equation of state of dark energy crossing -1, and the universe ends in the "Big Rip" phase. By using the Bayesian evidence as a model selection criterion to make the model comparison, we find that the holographic dark energy models are mildly favored by the observations compared with the $% \mathrm{\Lambda CDM}$ model.
Thursday, March 11, 2010
arXiv: 11 Mar 2010
Confirmation of general relativity on large scales from weak lensing and galaxy velocities
Authors: Reinabelle Reyes, Rachel Mandelbaum, Uros Seljak, Tobias Baldauf, James E. Gunn, Lucas Lombriser, Robert E. Smith
arXiv:1003.2185v1
Reyes, R. et al. 2010, Nature, 464, 256-258.
Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, EG, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to 'galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of EG different from the general relativistic prediction because, in these theories, the 'gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect3. Here we report that EG = 0.39 +/- 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of EG $\approx$ 0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.
The Milky Way rotation curve in Horava - Lifshitz theory
Authors: V.F. Cardone, N. Radicella, M.L. Ruggiero, M. Capone
arXiv:1003.2144v1
The Horava - Lifshitz (HL) theory has recently attracted a lot of interest as a viable solution to some quantum gravity related problems and the presence of an effective cosmological constant able to drive the cosmic speed up. We show here that, in the weak field limit, the HL proposal leads to a modification of the gravitational potential because of two additive terms (scaling respectively as $r^2$ and $r^{-4}$) to the Newtonian $1/r$ potential. We then derive a general expression to compute the rotation curve of an extended system under the assumption that the mass density only depends on the cylindrical coordinates $(R, z)$ showing that the HL modification induces a dependence of the circular velocity on the mass function which is a new feature of the theory. As a first exploratory analysis, we then try fitting the Milky Way rotation curve using its visible components only in order to see whether the HL modified potential can be an alternative to the dark matter framework. This turns out not to be the case so that we argue that dark matter is still needed, but the amount of dark matter and the dark halo density profile have to be revised according to the new HL potential.
Authors: Reinabelle Reyes, Rachel Mandelbaum, Uros Seljak, Tobias Baldauf, James E. Gunn, Lucas Lombriser, Robert E. Smith
arXiv:1003.2185v1
Reyes, R. et al. 2010, Nature, 464, 256-258.
Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, EG, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to 'galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of EG different from the general relativistic prediction because, in these theories, the 'gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect3. Here we report that EG = 0.39 +/- 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of EG $\approx$ 0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.
The Milky Way rotation curve in Horava - Lifshitz theory
Authors: V.F. Cardone, N. Radicella, M.L. Ruggiero, M. Capone
arXiv:1003.2144v1
The Horava - Lifshitz (HL) theory has recently attracted a lot of interest as a viable solution to some quantum gravity related problems and the presence of an effective cosmological constant able to drive the cosmic speed up. We show here that, in the weak field limit, the HL proposal leads to a modification of the gravitational potential because of two additive terms (scaling respectively as $r^2$ and $r^{-4}$) to the Newtonian $1/r$ potential. We then derive a general expression to compute the rotation curve of an extended system under the assumption that the mass density only depends on the cylindrical coordinates $(R, z)$ showing that the HL modification induces a dependence of the circular velocity on the mass function which is a new feature of the theory. As a first exploratory analysis, we then try fitting the Milky Way rotation curve using its visible components only in order to see whether the HL modified potential can be an alternative to the dark matter framework. This turns out not to be the case so that we argue that dark matter is still needed, but the amount of dark matter and the dark halo density profile have to be revised according to the new HL potential.
arXiv: 10 Mar 2010
The Post-quasistatic Approximation I: Shear Viscosity
Authors: C. Peralta, L. Rosales, B. Rodrí guez, W. Barreto
arXiv:1003.1825v1
In this first paper from a series of three, we apply the post-quasi--static approximation, an iterative method for the evolution of self-gravitating spheres of matter, to study the evolution of anisotropic non-adiabatic radiating and dissipative distributions in General Relativity. Dissipation is described by viscosity and free-streaming radiation, assuming an equation of state to model anisotropy induced by the shear viscosity. We match the interior solution, in non-comoving coordinates, with the Vaidya exterior solution. Two simple models are presented, based on the Schwarzschild and Tolman VI solutions, in the non--adiabatic and adiabatic limit. In both cases the eventual collapse or expansion of the distribution is mainly controlled by the anisotropy induced by the viscosity.
Cosmology of the Very Early Universe
Authors: Robert H. Brandenberger (McGill University)
arXiv:1003.1745v1
In these lectures I focus on early universe models which can explain the currently observed structure on large scales. I begin with a survey of inflationary cosmology, the current paradigm for understanding the origin of the universe as we observe it today. I will discuss some progress and problems in inflationary cosmology before moving on to a description of two alternative scenarios - the Matter Bounce and String Gas Cosmology. All early universe models connect to observations via the evolution of cosmological perturbations - a topic which will be discussed in detail in these lectures.
Authors: C. Peralta, L. Rosales, B. Rodrí guez, W. Barreto
arXiv:1003.1825v1
In this first paper from a series of three, we apply the post-quasi--static approximation, an iterative method for the evolution of self-gravitating spheres of matter, to study the evolution of anisotropic non-adiabatic radiating and dissipative distributions in General Relativity. Dissipation is described by viscosity and free-streaming radiation, assuming an equation of state to model anisotropy induced by the shear viscosity. We match the interior solution, in non-comoving coordinates, with the Vaidya exterior solution. Two simple models are presented, based on the Schwarzschild and Tolman VI solutions, in the non--adiabatic and adiabatic limit. In both cases the eventual collapse or expansion of the distribution is mainly controlled by the anisotropy induced by the viscosity.
Cosmology of the Very Early Universe
Authors: Robert H. Brandenberger (McGill University)
arXiv:1003.1745v1
In these lectures I focus on early universe models which can explain the currently observed structure on large scales. I begin with a survey of inflationary cosmology, the current paradigm for understanding the origin of the universe as we observe it today. I will discuss some progress and problems in inflationary cosmology before moving on to a description of two alternative scenarios - the Matter Bounce and String Gas Cosmology. All early universe models connect to observations via the evolution of cosmological perturbations - a topic which will be discussed in detail in these lectures.
Monday, March 8, 2010
arXiv: 9 Mar 2010
A simple model of the reflection effect for the interacting binaries and extrasolar planets
Authors: Jan Budaj
arXiv:1003.1662v1
Extrasolar planets are a natural extension of the interacting binaries towards the companions with very small masses and similar tools might be used to study them. Unfortunately, the generally accepted treatment of the reflection effect in interacting binaries cannot be applied to very cold objects irradiated by hot objects or to extrasolar planets. The aim of this paper is to develop a simple model of the reflection effect which could be easily incorporated into the present codes for modeling interacting binaries so that they can be used to study above mentioned objects. Our simple model of the reflection effect takes into account the reflection (scattering), heating and heat redistribution over the surface of the irradiated object. The shape of the objects is described by the Roche potential and limb and gravity darkening can be taken into account. The orbital revolution and rotation of the planet with proper Doppler shifts for the scattered and thermal radiation are also accounted for. The new model was incorporated into the code {\sc{shellspec}} which was originally designed for interacting binaries. Subsequently, light-curves of exoplanets (HD189733b) are modeled and the effects of the heat redistribution and limb darkening/brightening are studied. We also calculate the exact Roche shapes of all 63 transiting extrasolar planets known so far. It is found that the departures from the sphere vary considerably within the sample. Departures of about 1% are common. About 8% of planets show departures that exceed 3% (all of them have semi-major axes smaller than 0.03 AU). In some cases (WASP-12b, WASP-19b) departures reach about 10%.
A Measurement of the Rate of Type Ia Supernovae in Galaxy Clusters from the SDSS-II Supernova Survey
Authors: Benjamin Dilday, Bruce Bassett, Andrew Becker, Ralf Bender, Francisco Castander, David Cinabro, Joshua A. Frieman, Lluís Galbany, Peter Garnavich, Ariel Goobar, Ulrich Hopp, Yutaka Ihara, Saurabh W. Jha, Richard Kessler, Hubert Lampeitl, John Marriner, Ramon Miquel, Mercedes Mollá, Robert C. Nichol, Jakob Nordin, Adam G. Riess, Masao Sako, Donald P. Schneider, Mathew Smith, Jesper Sollerman, J. Craig Wheeler, Linda Östman, Dmitry Bizyaev, Howard Brewington, Elena Malanushenko, Viktor Malanushenko, Dan Oravetz, Kaike Pan, Audrey Simmons, Stephanie Snedden
arXiv:1003.1521v1
ABRIDGED We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z <0.17 x =" 10^{-12}">
Probability Distribution of Terrestrial Planets in Habitable Zones around Host Stars
Authors: Jianpo Guo, Fenghui Zhang, Xuefei Chen, Zhanwen Han
arXiv:1003.1368v1
With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system. We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars. Using Eggleton's code, we calculate the evolution of stars with masses less than 4.00 \mo. We also use the fitting formulae of stellar luminosity and radius, the boundary flux of habitable zones, the distribution of semimajor axis and mass of planets and the initial mass function of stars. We obtain the luminosity and radius of stars with masses from 0.08 to 4.00 \mo, and calculate the habitable zones of host stars, affected by stellar effective temperature. We achieve the probability distribution of terrestrial planets in habitable zones around host stars. We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion, and the number of terrestrial planets in habitable zones around K type stars is the most, in the Milky Way.
Potential dominated scalar-tensor cosmologies in the general relativity limit: phase space view
Authors: Laur Jarv, Piret Kuusk, Margus Saal
arXiv:1003.1686v1
We consider the potential dominated era of Friedmann-Lemaitre-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling functions, and focus upon the phase space of the scalar field. To study the regime suggested by the local weak field tests (i.e. close to the so-called limit of general relativity) we propose a nonlinear approximation scheme, solve for the phase trajectories, and provide a complete classification of possible phase portraits. We argue that the topology of trajectories in the nonlinear approximation is representative of those of the full system, and thus can tell for which scalar-tensor models general relativity functions as an attractor.
Authors: Jan Budaj
arXiv:1003.1662v1
Extrasolar planets are a natural extension of the interacting binaries towards the companions with very small masses and similar tools might be used to study them. Unfortunately, the generally accepted treatment of the reflection effect in interacting binaries cannot be applied to very cold objects irradiated by hot objects or to extrasolar planets. The aim of this paper is to develop a simple model of the reflection effect which could be easily incorporated into the present codes for modeling interacting binaries so that they can be used to study above mentioned objects. Our simple model of the reflection effect takes into account the reflection (scattering), heating and heat redistribution over the surface of the irradiated object. The shape of the objects is described by the Roche potential and limb and gravity darkening can be taken into account. The orbital revolution and rotation of the planet with proper Doppler shifts for the scattered and thermal radiation are also accounted for. The new model was incorporated into the code {\sc{shellspec}} which was originally designed for interacting binaries. Subsequently, light-curves of exoplanets (HD189733b) are modeled and the effects of the heat redistribution and limb darkening/brightening are studied. We also calculate the exact Roche shapes of all 63 transiting extrasolar planets known so far. It is found that the departures from the sphere vary considerably within the sample. Departures of about 1% are common. About 8% of planets show departures that exceed 3% (all of them have semi-major axes smaller than 0.03 AU). In some cases (WASP-12b, WASP-19b) departures reach about 10%.
A Measurement of the Rate of Type Ia Supernovae in Galaxy Clusters from the SDSS-II Supernova Survey
Authors: Benjamin Dilday, Bruce Bassett, Andrew Becker, Ralf Bender, Francisco Castander, David Cinabro, Joshua A. Frieman, Lluís Galbany, Peter Garnavich, Ariel Goobar, Ulrich Hopp, Yutaka Ihara, Saurabh W. Jha, Richard Kessler, Hubert Lampeitl, John Marriner, Ramon Miquel, Mercedes Mollá, Robert C. Nichol, Jakob Nordin, Adam G. Riess, Masao Sako, Donald P. Schneider, Mathew Smith, Jesper Sollerman, J. Craig Wheeler, Linda Östman, Dmitry Bizyaev, Howard Brewington, Elena Malanushenko, Viktor Malanushenko, Dan Oravetz, Kaike Pan, Audrey Simmons, Stephanie Snedden
arXiv:1003.1521v1
ABRIDGED We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z <0.17 x =" 10^{-12}">
Probability Distribution of Terrestrial Planets in Habitable Zones around Host Stars
Authors: Jianpo Guo, Fenghui Zhang, Xuefei Chen, Zhanwen Han
arXiv:1003.1368v1
With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system. We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars. Using Eggleton's code, we calculate the evolution of stars with masses less than 4.00 \mo. We also use the fitting formulae of stellar luminosity and radius, the boundary flux of habitable zones, the distribution of semimajor axis and mass of planets and the initial mass function of stars. We obtain the luminosity and radius of stars with masses from 0.08 to 4.00 \mo, and calculate the habitable zones of host stars, affected by stellar effective temperature. We achieve the probability distribution of terrestrial planets in habitable zones around host stars. We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion, and the number of terrestrial planets in habitable zones around K type stars is the most, in the Milky Way.
Potential dominated scalar-tensor cosmologies in the general relativity limit: phase space view
Authors: Laur Jarv, Piret Kuusk, Margus Saal
arXiv:1003.1686v1
We consider the potential dominated era of Friedmann-Lemaitre-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling functions, and focus upon the phase space of the scalar field. To study the regime suggested by the local weak field tests (i.e. close to the so-called limit of general relativity) we propose a nonlinear approximation scheme, solve for the phase trajectories, and provide a complete classification of possible phase portraits. We argue that the topology of trajectories in the nonlinear approximation is representative of those of the full system, and thus can tell for which scalar-tensor models general relativity functions as an attractor.
Sunday, March 7, 2010
arXiv: 8 Mar 2010
Analytic Methods for Cosmological Likelihoods
Authors: A. N. Taylor, T. D. Kitching
arXiv:1003.1136v1
We present general, analytic methods for Cosmological likelihood analysis and solve the "many-parameters" problem in Cosmology. Maxima are found by Newton's Method, while marginalization over nuisance parameters, and parameter errors and covariances are estimated by analytic marginalization of an arbitrary likelihood function with flat or Gaussian priors. We show that information about remaining parameters is preserved by marginalization. Marginalizing over all parameters, we find an analytic expression for the Bayesian evidence for model selection. We apply these methods to data described by Gaussian likelihoods with parameters in the mean and covariance. This method can speed up conventional likelihood analysis by orders of magnitude when combined with Monte-Carlo Markov Chain methods, while Bayesian model selection becomes effectively instantaneous.
Authors: A. N. Taylor, T. D. Kitching
arXiv:1003.1136v1
We present general, analytic methods for Cosmological likelihood analysis and solve the "many-parameters" problem in Cosmology. Maxima are found by Newton's Method, while marginalization over nuisance parameters, and parameter errors and covariances are estimated by analytic marginalization of an arbitrary likelihood function with flat or Gaussian priors. We show that information about remaining parameters is preserved by marginalization. Marginalizing over all parameters, we find an analytic expression for the Bayesian evidence for model selection. We apply these methods to data described by Gaussian likelihoods with parameters in the mean and covariance. This method can speed up conventional likelihood analysis by orders of magnitude when combined with Monte-Carlo Markov Chain methods, while Bayesian model selection becomes effectively instantaneous.
Saturday, March 6, 2010
The Astrophysical Journal / 24/2/2010
Dark Fluid: A Unified Framework for Modified Newtonian Dynamics,
Dark Matter, and Dark Energy
HongSheng Zhao and Baojiu Li
2010 ApJ 712 130-141
Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/130
Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/130/apj_712_1_130.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/130/apj_712_1_130.html
Empirical theories of dark matter (DM) like modified Newtonian
dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity
were motivated by astronomical data. But could these theories be
branches rooted from a more general and hence generic framework?
Here we propose a very generic Lagrangian of such a framework based
on simple dimensional analysis and covariant symmetry requirements,
and explore various outcomes in a top-down fashion. The desired
effects of quintessence plus cold DM particle fields or MOND-like
scalar field(s) are shown to be largely achievable by one vector
field only. Our framework preserves the covariant formulation of
general relativity, but allows the expanding physical metric to be
bent by a single new species of dark fluid flowing in spacetime. Its
non-uniform stress tensor and current vector are simple functions of
a vector field with variable norm, not coupled with the baryonic
fluid and the four-vector potential of the photon fluid. The dark
fluid framework generically branches into a continuous spectrum of
theories with DE and DM effects, including the f(R) gravity,
tensor-vector-scalar-like theories, Einstein-Aether, and nL theories
as limiting cases. When the vector field degenerates into a pure
scalar field, we obtain the physics for quintessence. Choices of
parameters can be made to pass Big Bang nucleosynthesis,
parameterized post-Newtonian, and causality constraints. In this
broad setting we emphasize the non-constant dynamical field behind
the cosmological constant effect, and highlight plausible
corrections beyond the classical MOND predictions.
Observations of Milky Way Dwarf Spheroidal Galaxies with the Fermi-Large Area Telescope Detector and Constraints on Dark Matter Models A. A. Abdo, M. Ackermann, M. Ajello, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, E. D. Bloom, E. Bonamente, A. W. Borgland, J. Bregeon, A. Brez, M. Brigida, P. Bruel, T. H. Burnett, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, C. Cecchi, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, A. de Angelis, F. de Palma, S. W. Digel, E. do Couto e Silva, P. S. Drell, A. Drlica-Wagner, R. Dubois, D. Dumora, C. Farnier, C. Favuzzi, S. J. Fegan, W. B. Focke, P. Fortin, M. Frailis, Y. Fukazawa, P. Fusco, F. Gargano, N. Gehrels, S. Germani, B. Giebels, N. Giglietto, F. Giordano, T. Glanzman, G. Godfrey, I. A. Grenier, J. E. Grove, L. Guillemot, S. Guiriec, M. Gustafsson, A. K. Harding, E. Hays, D. Horan, R. E. Hughes, M. S. Jackson, T. E. Jeltema, G. Johannesson, A. S. Johnson, R. P. Johnson, W. N. Johnson, T. Kamae, H. Katagiri, J. Kataoka, M. Kerr, J. Knodlseder, M. Kuss, J. Lande, L. Latronico, M. Lemoine-Goumard, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, A. Makeev, M. N. Mazziotta, J. E. McEnery, C. Meurer, P. F. Michelson, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, E. Moretti, A. Morselli, I. V. Moskalenko, S. Murgia, P. L. Nolan, J. P. Norris, E. Nuss, T. Ohsugi, N. Omodei, E. Orlando, J. F. Ormes, D. Paneque, J. H. Panetta, D. Parent, V. Pelassa, M. Pepe, M. Pesce-Rollins, F. Piron, T. A. Porter, S. Profumo, S. Raino, R. Rando, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, A. Y. Rodriguez, M. Roth, H. F.-W. Sadrozinski, A. Sander, P. M. Saz Parkinson, J. D. Scargle, T. L. Schalk, A. Sellerholm, C. Sgro, E. J. Siskind, D. A. Smith, P. D. Smith, G. Spandre, P. Spinelli, M. S. Strickman, D. J. Suson, H. Takahashi, T. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, A. Tramacere, Y. Uchiyama, T. L. Usher, V. Vasileiou, N. Vilchez, V. Vitale, A. P. Waite, P. Wang, B. L. Winer, K. S. Wood, T. Ylinen, M. Ziegler, James S. Bullock, Manoj Kaplinghat, and Gregory D. Martinez 2010 ApJ 712 147-158 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/147 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/147/apj_712_1_147.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/147/apj_712_1_147.html
We report on the observations of 14 dwarf spheroidal galaxies (dSphs) with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky g-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected g-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dSphs, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant g-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the g-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10-9 photons cm-2 s-1. Using recent stellar kinematic data, the g-ray flux limits are combined with improved determinations of the dark matter density profile in eight of the 14 candidate dwarfs to place limits on the pair-annihilation cross section of WIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g., in models where supersymmetry breaking occurs via anomaly mediation. The g-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e + e - data, including low-mass wino-like neutralinos and models with TeV masses pair annihilating into muon-antimuon pairs.
Type I Planet Migration in Nearly Laminar Disks: Long-Term Behavior C. Yu, H. Li, S. Li, S. H. Lubow, and D. N. C. Lin 2010 ApJ 712 198-208 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/198 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/198/apj_712_1_198.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/198/apj_712_1_198.html
We carry out two-dimensional high-resolution numerical simulations of type I planet migration with different disk viscosities. We find that the planet migration is strongly dependent on disk viscosities. Two kinds of density wave damping mechanisms are discussed. Accordingly, the angular momentum transport can be either viscosity dominated or shock dominated, depending on the disk viscosities. The long-term migration behavior is different as well. Influences of the Rossby vortex instability on planet migration are also discussed. In addition, we investigate very weak shock generation in inviscid disks by small mass planets and compare the results with prior analytic results.
The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II Supernova Survey Brian T. Hayden, Peter M. Garnavich, Richard Kessler, Joshua A. Frieman, Saurabh W. Jha, Bruce Bassett, David Cinabro, Benjamin Dilday, Daniel Kasen, John Marriner, Robert C. Nichol, Adam G. Riess, Masao Sako, Donald P. Schneider, Mathew Smith, and Jesper Sollerman 2010 ApJ 712 350-366 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/350 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/350/apj_712_1_350.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/350/apj_712_1_350.html
We analyze the rise and fall times of Type Ia supernova (SN Ia) light curves discovered by the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. From a set of 391 light curves k-corrected to the rest-frame B and V bands, we find a smaller dispersion in the rising portion of the light curve compared to the decline. This is in qualitative agreement with computer models which predict that variations in radioactive nickel yield have less impact on the rise than on the spread of the decline rates. The differences we find in the rise and fall properties suggest that a single "stretch" correction to the light curve phase does not properly model the range of SN Ia light curve shapes. We select a subset of 105 light curves well observed in both rise and fall portions of the light curves and develop a "2-stretch" fit algorithm which estimates the rise and fall times independently. We find the average time from explosion to B-band peak brightness is 17.38 +- 0.17 days, but with a spread of rise times which range from 13 days to 23 days. Our average rise time is shorter than the 19.5 days found in previous studies; this reflects both the different light curve template used and the application of the 2-stretch algorithm. The SDSS-II supernova set and the local SNe Ia with well-observed early light curves show no significant differences in their average rise-time properties. We find that slow-declining events tend to have fast rise times, but that the distribution of rise minus fall time is broad and single peaked. This distribution is in contrast to the bimodality in this parameter that was first suggested by Strovink from an analysis of a small set of local SNe Ia. We divide the SDSS-II sample in half based on the rise minus fall value, tr - tf [?] 2 days and tr - tf > 2 days, to search for differences in their host galaxy properties and Hubble residuals; we find no difference in host galaxy properties or Hubble residuals in our sample.
Dark Matter, and Dark Energy
HongSheng Zhao and Baojiu Li
2010 ApJ 712 130-141
Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/130
Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/130/apj_712_1_130.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/130/apj_712_1_130.html
Empirical theories of dark matter (DM) like modified Newtonian
dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity
were motivated by astronomical data. But could these theories be
branches rooted from a more general and hence generic framework?
Here we propose a very generic Lagrangian of such a framework based
on simple dimensional analysis and covariant symmetry requirements,
and explore various outcomes in a top-down fashion. The desired
effects of quintessence plus cold DM particle fields or MOND-like
scalar field(s) are shown to be largely achievable by one vector
field only. Our framework preserves the covariant formulation of
general relativity, but allows the expanding physical metric to be
bent by a single new species of dark fluid flowing in spacetime. Its
non-uniform stress tensor and current vector are simple functions of
a vector field with variable norm, not coupled with the baryonic
fluid and the four-vector potential of the photon fluid. The dark
fluid framework generically branches into a continuous spectrum of
theories with DE and DM effects, including the f(R) gravity,
tensor-vector-scalar-like theories, Einstein-Aether, and nL theories
as limiting cases. When the vector field degenerates into a pure
scalar field, we obtain the physics for quintessence. Choices of
parameters can be made to pass Big Bang nucleosynthesis,
parameterized post-Newtonian, and causality constraints. In this
broad setting we emphasize the non-constant dynamical field behind
the cosmological constant effect, and highlight plausible
corrections beyond the classical MOND predictions.
Observations of Milky Way Dwarf Spheroidal Galaxies with the Fermi-Large Area Telescope Detector and Constraints on Dark Matter Models A. A. Abdo, M. Ackermann, M. Ajello, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, E. D. Bloom, E. Bonamente, A. W. Borgland, J. Bregeon, A. Brez, M. Brigida, P. Bruel, T. H. Burnett, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, C. Cecchi, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, A. de Angelis, F. de Palma, S. W. Digel, E. do Couto e Silva, P. S. Drell, A. Drlica-Wagner, R. Dubois, D. Dumora, C. Farnier, C. Favuzzi, S. J. Fegan, W. B. Focke, P. Fortin, M. Frailis, Y. Fukazawa, P. Fusco, F. Gargano, N. Gehrels, S. Germani, B. Giebels, N. Giglietto, F. Giordano, T. Glanzman, G. Godfrey, I. A. Grenier, J. E. Grove, L. Guillemot, S. Guiriec, M. Gustafsson, A. K. Harding, E. Hays, D. Horan, R. E. Hughes, M. S. Jackson, T. E. Jeltema, G. Johannesson, A. S. Johnson, R. P. Johnson, W. N. Johnson, T. Kamae, H. Katagiri, J. Kataoka, M. Kerr, J. Knodlseder, M. Kuss, J. Lande, L. Latronico, M. Lemoine-Goumard, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, A. Makeev, M. N. Mazziotta, J. E. McEnery, C. Meurer, P. F. Michelson, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, E. Moretti, A. Morselli, I. V. Moskalenko, S. Murgia, P. L. Nolan, J. P. Norris, E. Nuss, T. Ohsugi, N. Omodei, E. Orlando, J. F. Ormes, D. Paneque, J. H. Panetta, D. Parent, V. Pelassa, M. Pepe, M. Pesce-Rollins, F. Piron, T. A. Porter, S. Profumo, S. Raino, R. Rando, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, A. Y. Rodriguez, M. Roth, H. F.-W. Sadrozinski, A. Sander, P. M. Saz Parkinson, J. D. Scargle, T. L. Schalk, A. Sellerholm, C. Sgro, E. J. Siskind, D. A. Smith, P. D. Smith, G. Spandre, P. Spinelli, M. S. Strickman, D. J. Suson, H. Takahashi, T. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, A. Tramacere, Y. Uchiyama, T. L. Usher, V. Vasileiou, N. Vilchez, V. Vitale, A. P. Waite, P. Wang, B. L. Winer, K. S. Wood, T. Ylinen, M. Ziegler, James S. Bullock, Manoj Kaplinghat, and Gregory D. Martinez 2010 ApJ 712 147-158 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/147 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/147/apj_712_1_147.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/147/apj_712_1_147.html
We report on the observations of 14 dwarf spheroidal galaxies (dSphs) with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky g-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected g-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dSphs, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant g-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the g-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10-9 photons cm-2 s-1. Using recent stellar kinematic data, the g-ray flux limits are combined with improved determinations of the dark matter density profile in eight of the 14 candidate dwarfs to place limits on the pair-annihilation cross section of WIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g., in models where supersymmetry breaking occurs via anomaly mediation. The g-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e + e - data, including low-mass wino-like neutralinos and models with TeV masses pair annihilating into muon-antimuon pairs.
Type I Planet Migration in Nearly Laminar Disks: Long-Term Behavior C. Yu, H. Li, S. Li, S. H. Lubow, and D. N. C. Lin 2010 ApJ 712 198-208 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/198 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/198/apj_712_1_198.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/198/apj_712_1_198.html
We carry out two-dimensional high-resolution numerical simulations of type I planet migration with different disk viscosities. We find that the planet migration is strongly dependent on disk viscosities. Two kinds of density wave damping mechanisms are discussed. Accordingly, the angular momentum transport can be either viscosity dominated or shock dominated, depending on the disk viscosities. The long-term migration behavior is different as well. Influences of the Rossby vortex instability on planet migration are also discussed. In addition, we investigate very weak shock generation in inviscid disks by small mass planets and compare the results with prior analytic results.
The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II Supernova Survey Brian T. Hayden, Peter M. Garnavich, Richard Kessler, Joshua A. Frieman, Saurabh W. Jha, Bruce Bassett, David Cinabro, Benjamin Dilday, Daniel Kasen, John Marriner, Robert C. Nichol, Adam G. Riess, Masao Sako, Donald P. Schneider, Mathew Smith, and Jesper Sollerman 2010 ApJ 712 350-366 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/350 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/350/apj_712_1_350.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/350/apj_712_1_350.html
We analyze the rise and fall times of Type Ia supernova (SN Ia) light curves discovered by the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. From a set of 391 light curves k-corrected to the rest-frame B and V bands, we find a smaller dispersion in the rising portion of the light curve compared to the decline. This is in qualitative agreement with computer models which predict that variations in radioactive nickel yield have less impact on the rise than on the spread of the decline rates. The differences we find in the rise and fall properties suggest that a single "stretch" correction to the light curve phase does not properly model the range of SN Ia light curve shapes. We select a subset of 105 light curves well observed in both rise and fall portions of the light curves and develop a "2-stretch" fit algorithm which estimates the rise and fall times independently. We find the average time from explosion to B-band peak brightness is 17.38 +- 0.17 days, but with a spread of rise times which range from 13 days to 23 days. Our average rise time is shorter than the 19.5 days found in previous studies; this reflects both the different light curve template used and the application of the 2-stretch algorithm. The SDSS-II supernova set and the local SNe Ia with well-observed early light curves show no significant differences in their average rise-time properties. We find that slow-declining events tend to have fast rise times, but that the distribution of rise minus fall time is broad and single peaked. This distribution is in contrast to the bimodality in this parameter that was first suggested by Strovink from an analysis of a small set of local SNe Ia. We divide the SDSS-II sample in half based on the rise minus fall value, tr - tf [?] 2 days and tr - tf > 2 days, to search for differences in their host galaxy properties and Hubble residuals; we find no difference in host galaxy properties or Hubble residuals in our sample.
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