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

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} <>

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.

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.

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.

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.

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.

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.

arXiv: 5 Mar 2010

Bullet Cluster: A Challenge to LCDM Cosmology
Authors: Jounghun Lee (Seoul Nat'l U.), Eiichiro Komatsu (U.Texas at Austin)
arXiv:1003.0939v1
To quantify how rare the bullet-cluster-like high-velocity merging systems are in the standard LCDM cosmology, we use a large-volume 27 (Gpc/h)^3 MICE simulation to calculate the distribution of infall velocities of subclusters around massive main clusters. The infall-velocity distribution is given at (1-3)R_{200} of the main cluster (where R_{200} is similar to the virial radius), and thus it gives the distribution of realistic initial velocities of subclusters just before collision. These velocities can be compared with the initial velocities used by the non-cosmological hydrodynamical simulations of 1E0657-56 in the literature. The latest parameter search carried out by Mastropietro & Burkert (2008) showed that the initial velocity of 3000 km/s at about 2R_{200} is required to explain the observed shock velocity, X-ray brightness ratio of the main and subcluster, and displacement of the X-ray peaks from the mass peaks. We show that such a high infall velocity at 2R_{200} is incompatible with the prediction of a LCDM model: the probability of finding 3000 km/s in (2-3)R_{200} is between 3.3X10^{-11} and 3.6X10^{-9}. It is concluded that the existence of 1E0657-56 is incompatible with the prediction of a LCDM model, unless a lower infall velocity solution for 1E0657-56 with <>

Power spectrum extraction for redshifted 21-cm epoch of reionization experiments: the LOFAR case
Authors: Geraint Harker, Saleem Zaroubi, Gianni Bernardi, Michiel A. Brentjens, A. G. de Bruyn, Benedetta Ciardi, Vibor Jelic, Leon V. E. Koopmans, Panagiotis Labropoulos, Garrelt Mellema, Andre Offringa, V. N. Pandey, Andreas H. Pawlik, Joop Schaye, Rajat M. Thomas, Sarod Yatawatta
arXiv:1003.0965v1
One of the aims of the Low Frequency Array (LOFAR) Epoch of Reionization (EoR) project is to measure the power spectrum of variations in the intensity of redshifted 21-cm radiation from the EoR. The sensitivity with which this power spectrum can be estimated depends on the level of thermal noise and sample variance, and also on the systematic errors arising from the extraction process, in particular from the subtraction of foreground contamination. We model the extraction process using realistic simulations of the cosmological signal, the foregrounds and noise, and so estimate the sensitivity of the LOFAR EoR experiment to the redshifted 21-cm power spectrum. Detection of emission from the EoR should be possible within 360 hours of observation with a single station beam. Integrating for longer, and synthesizing multiple station beams within the primary (tile) beam, then enables us to extract progressively more accurate estimates of the power at a greater range of scales and redshifts. We discuss different observational strategies which compromise between depth of observation, sky coverage and frequency coverage. A plan in which lower frequencies receive a larger fraction of the time appears to be promising. We also study the nature of the bias which foreground fitting errors induce on the inferred power spectrum, and discuss how to reduce and correct for this bias. The angular and line-of-sight power spectra have different merits in this respect, and we suggest considering them separately in the analysis of LOFAR data.

Do primordial Lithium abundances imply there's no Dark Energy?
Authors: Marco Regis, Chris Clarkson (Cape Town)
arXiv:1003.1043v1
Explaining the well established observation that the expansion rate of the universe is apparently accelerating is one of the defining scientific problems of our age. Within the standard model of cosmology, the repulsive `dark energy' supposedly responsible has no explanation at a fundamental level, despite many varied attempts. A further important dilemma in the standard model is the Lithium problem, which is the substantial mismatch between the theoretical prediction for 7-Li from Big Bang Nucleosynthesis and the value that we observe today. This observation is one of the very few we have from along our past worldline as opposed to our past lightcone. By releasing the untested assumption that the universe is homogeneous on very large scales, both apparent acceleration and the Lithium problem can be easily accounted for as different aspects of cosmic inhomogeneity, without causing problems for other cosmological phenomena such as the cosmic microwave background. We illustrate this in the context of a void model.

The effect of redshift-space distortions on projected 2-pt clustering measurements
Authors: Kelly Nock, Will J. Percival, Ashley J. Ross
arXiv:1003.0896v1
Although redshift-space distortions only affect inferred distances and not angles, they still distort the projected angular clustering of galaxy samples selected using redshift dependent quantities. From an Eulerian view-point, this effect is caused by the apparent movement of galaxies into or out of the sample. From a Lagrangian view-point, we find that projecting the redshift-space overdensity field over a finite radial distance does not remove all the anisotropic distortions. We investigate this effect, showing that it strongly boosts the amplitude of clustering for narrow samples and can also reduce the significance of baryonic features in the correlation function. We argue that the effect can be mitigated by binning in apparent galaxy pair-centre rather than galaxy position, and applying an upper limit to the radial galaxy separation. We demonstrate this approach, contrasting against standard top-hat binning in galaxy distance, using sub-samples taken from the Hubble Volume simulations. Using a simple model for the radial distribution expected for galaxies from a survey such as the Dark Energy Survey (DES), we show that this binning scheme will simplify analyses that will measure baryonic acoustic oscillations within such galaxy samples. This technique can also be used to measure the amplitude of the redshift-space distortions. Our analysis is relevant for other photometric redshift surveys, including those made by the Panoramic Survey Telescope & Rapid Response System (Pan-Starrs) and the Large Synoptic Survey Telescope (LSST).

Dark Matter Candidates from Particle Physics and Methods of Detection
Authors: Jonathan L. Feng
arXiv:1003.0904v1
61 pages, to appear in Annual Reviews of Astronomy and Astrophysics
The identity of dark matter is a question of central importance in both astrophysics and particle physics. In the past, the leading particle candidates were cold and collisionless, and typically predicted missing energy signals at particle colliders. However, recent progress has greatly expanded the list of well-motivated candidates and the possible signatures of dark matter. This review begins with a brief summary of the standard model of particle physics and its outstanding problems. We then discuss several dark matter candidates motivated by these problems, including WIMPs, superWIMPs, light gravitinos, hidden dark matter, sterile neutrinos, and axions. For each of these, we critically examine the particle physics motivations and present their expected production mechanisms, basic properties, and implications for direct and indirect detection, particle colliders, and astrophysical observations. Upcoming experiments will discover or exclude many of these candidates, and progress may open up an era of unprecedented synergy between studies of the largest and smallest observable length scales.

arXiv: 4 Mar 2010

Spin and structural halo properties at high redshift in a LCDM Universe
Authors: Andrew J. Davis, Priyamvada Natarajan
arXiv:1003.0670v1
In this paper, we examine in detail the key structural properties of high redshift dark matter haloes as a function of their spin parameter. We perform and analyze high resolution cosmological simulations of the formation of structure in a LCDM Universe. We study the mass function, ellipticities, shapes, density profiles, rotation curves and virialization for a large sample of dark matter haloes from z = 15 - 6. We also present detailed convergence tests for individual haloes. We find that high spin haloes have stronger clustering strengths (up to 25%) at all mass and redshift ranges at these early epochs. High redshift spherical haloes are also up to 50% more clustered than aspherical haloes. High spin haloes at these redshifts are also preferentially found in high density environments, and have more neighbors than their low spin counterparts. We report a systematic offset in the peak of the circular velocity curves for high and low spin haloes of the same mass. Therefore, estimating halo masses without knowledge of the spin, using only the circular velocity can yield errors of up to 40%. The strong dependence of key structural properties on spin that we report here likely have important implications for studies of star formation and feedback from these galaxies.

Reconstructing Redshift Distributions with Cross-Correlations: Tests and an Optimized Recipe
Authors: Daniel J. Matthews, Jeffrey A. Newman
arXiv:1003.0687v1
Many of the cosmological tests to be performed by planned dark energy experiments will require extremely well-characterized photometric redshift measurements. Current estimates are that the true mean redshift of the objects in each photo-z bin must be known to better than 0.002(1+z) if errors in cosmological measurements are not to be degraded. A conventional approach is to calibrate these photometric redshifts with large sets of spectroscopic redshifts. However, at the depths probed by Stage III surveys (such as DES), let alone Stage IV (LSST, JDEM, Euclid), existing large redshift samples have all been highly (25-60%) incomplete. A powerful alternative approach is to exploit the clustering of galaxies to perform photometric redshift calibrations. Measuring the two-point angular cross-correlation between objects in some photometric redshift bin and objects with known spectroscopic redshift allows the true redshift distribution of a photometric sample to be reconstructed in detail, even if it includes objects too faint for spectroscopy or if spectroscopic samples are highly incomplete. We test this technique using mock DEEP2 Galaxy Redshift survey light cones constructed from the Millennium Simulation semi-analytic galaxy catalogs. From this realistic test, we find that the true redshift distribution of a photometric sample can, in fact, be determined accurately with cross-correlation techniques. We also compare the empirical error in the reconstruction of redshift distributions to previous analytic predictions, finding that additional components must be included in error budgets to match the simulation results. We conclude by presenting a step-by-step, optimized recipe for reconstructing redshift distributions using standard correlation measurements.

Title: Model-independent cosmological constraints from the CMB
Authors: Marc Vonlanthen, Syksy Rasanen, Ruth Durrer
arXiv:1003.0810v1
We analyse CMB data in a manner which is as model-independent as possible. We encode the effects of late-time cosmology into a single parameter which determines the distance to the last scattering surface. We exclude low multipoles $\ell<40$ omega_b ="2.13\pm" omega_c="0.124\pm" n_s="0.93\pm" theta_a="0.593\pm">

arXiv: 3 Mar 2010

Pervasive Orbital Eccentricities Dictate the Habitability of Extrasolar Earths
Authors: Ryosuke Kita, Frederic A. Rasio, Genya Takeda (Northwestern University)
arXiv:1003.0633v2 [
The long-term habitability of Earth-like planets requires low orbital eccentricities. A secular perturbation from a distant stellar companion is a very important mechanism in exciting planetary eccentricities, as many of the extrasolar planetary systems are associated with stellar companions. Although the orbital evolution of an Earth-like planet in a stellar binary is well understood, the effect of a binary perturbation to a more realistic system containing additional gas giant planets has been very little studied. Here we provide analytic criteria confirmed by a large ensemble of numerical integrations that identify the initial orbital parameters leading to eccentric orbits. We show that an extra-solar earth is likely to experience a broad range of orbital evolution dictated by the location of a gas-giant planet, necessitating more focused studies on the effect of eccentricity on the potential for life.

Stable and habitable systems with two giant planets
Authors: Vera Dobos, Imre Nagy, Judit Orgoványi
arXiv:1003.0570v1
We have studied planetary systems which are similar to the Solar System and built up from three inner rocky planets (Venus, Earth, Mars) and two outer gas giants. The stability of the orbits of the inner planets is discussed in the cases of different masses of the gas planets. To demonstrate the results stability maps were made and it was found that Jupiter could be four times and Saturn could be three times more massive while the orbits of the inner planets stay stable. Similar calculations were made by changing the mass of the Sun. In this case the position of the rocky planets and the extension of the liquid water habitable and the UV habitable zones were studied for different masses of the Sun. It was found that the orbits of the planets were stable for values greater than 0.33 M_Sun where M_Sun is the mass of the Sun and at lower masses of the Sun (at about 0.8 M_Sun) only Venus, but for higher mass values (at about 1.2 M_Sun) Earth and also Mars are located in both habitable zones.

The cosmic microwave background bispectrum from the non-linear evolution of the cosmological perturbations
Authors: Cyril Pitrou, Jean-Philippe Uzan, Francis Bernardeau
arXiv:1003.0481v1
This article presents the first computation of the complete bispectrum of the cosmic microwave background temperature anisotropies arising from the evolution of all cosmic fluids up to second order, including neutrinos. Gravitational couplings, electron density fluctuations and the second order Boltzmann equation are fully taken into account. Comparison to limiting cases that appeared previously in the literature are provided. These are regimes for which analytical insights can be given. The final results are expressed in terms of equivalent fNL for different configurations. It is found that for moments up to lmax=2000, the signal generated by non-linear effects is equivalent to fNL~5 for both local-type and equilateral-type primordial non-Gaussianity.

Analytical Approach for the Determination of the Luminosity Distance in a Flat Universe with Dark Energy
Authors: T. Wickramasinghe, T. N. Ukwatta
arXiv:1003.0483v1
Recent cosmological observations indicate that the present universe is flat and dark energy dominated. In such a universe, the calculation of the luminosity distance, d_L, involve repeated numerical calculations. In this paper, it is shown that a quite efficient approximate analytical expression, having very small uncertainties, can be obtained for d_L. The analytical calculation is shown to be exceedingly efficient, as compared to the traditional numerical methods and is potentially useful for Monte-Carlo simulations involving luminosity distances.

Casimir effect in a weak gravitational field and the spacetime index of refraction
Authors: B. Nazari, M. Nouri-Zonoz
arXiv:1003.0614v1
In a recent paper [arXiv:0904.2904] using a conjecture it is shown how one can calculate the effect of a weak stationary gravitational field on vacuum energy in the context of Casimir effect in an external gravitational field treated in 1+3 formulation of spacetime decomposition.. In this article, employing quntum field theory in curved spacetime, we explicitly calculate the effect of a weak static gravitational field on virtual massless scalar particles in a Casimir apparatus. It is shown that, as expected from the proposed conjecture, both the frequency and renormalized energy of the virtual scalar field are affected by the gravitational field through its index of refraction. This could be taken as a strong evidence in favour of the proposed conjecture. Generalizations to weak {\it stationary} spacetimes and virtual photons are also discussed.

arXiv: 2 Mar 2010

Dynamical Masses in Modified Gravity
Authors: Fabian Schmidt
arXiv:1003.0409v1
Differences in masses inferred from dynamics, such as velocity dispersions or X-rays, and those inferred from lensing are a generic prediction of modified gravity theories. Viable models however must include some non-linear mechanism to restore General Relativity (GR) in dense environments, which is necessary to pass Solar System constraints on precisely these deviations. In this paper, we study the dynamics within virialized structures in the context of two modified gravity models, f(R) gravity and DGP. The non-linear mechanisms to restore GR, which f(R) and DGP implement in very different ways, have a strong impact on the dynamics in bound objects; they leave distinctive signatures in the dynamical mass-lensing mass relation as a function of mass and radius. We present measurements from N-body simulations of f(R) and DGP, as well as semi-analytical models which match the simulation results to surprising accuracy in both cases. The semi-analytical models are useful for making the connection to observations. Our results confirm that the environment- and scale-dependence of the modified gravity effects have to be taken into account when confronting gravity theories with observations of dynamics in galaxies and clusters.

Orbital period variations of hot-Jupiters caused by the Applegate effect
Authors: C. A. Watson (1), T. R. Marsh (2) ((1) Queen's University Belfast, (2) University of Warwick)
arXiv:1003.0340v1
Several authors have shown that precise measurements of transit time variations of exoplanets can be sensitive to other planetary bodies, such as exo-moons. In addition, the transit timing variations of the exoplanets closest to their host stars can provide tests of tidal dissipation theory. These studies, however, have not considered the effect of the host star. There is a large body of observational evidence that eclipse times of binary stars can vary dramatically due to variations in the quadrupole moment of the stars driven by stellar activity. In this paper we investigate and estimate the likely impact such variations have on the transit times of exoplanets. We find in several cases that such variations should be detectable. In particular, the estimated period changes for WASP-18b are of the same order as those expected for tidal dissipation, even for relatively low values of the tidal dissipation parameter. The transit time variations caused by the Applegate mechanism are also of the correct magnitude and occur on timescales such that they may be confused with variations caused by light-time travel effects due to the presence of a Jupiter-like second planet. Finally, we suggest that transiting exoplanet systems may provide a clean route (compared to binaries) to constraining the type of dynamo operating in the host star.

Title: The local B-polarization of the CMB: a very sensitive probe of cosmic defects
Autharors: Juan Garcia-Bellido, Ruth Durrer, Elisa Fenu, Daniel G. Figueroa, Martin Kunz
arXiv:1003.0299v1
We present a new and especially powerful signature of cosmic strings and other topological or non-topological defects in the polarization of the cosmic microwave background (CMB). We show that even if defects contribute 1% or less in the CMB temperature anisotropy spectrum, their signature in the local $\tilde{B}$-polarization correlation function at angular scales of tens of arc minutes is much larger than that due to gravitational waves from inflation, even if the latter contribute with a ratio as big as $r\simeq 0.1$ to the temperature anisotropies. Proposed B-polarization experiments, with a good sensitivity on arcminute scales, may either detect a contribution from topological defects produced after inflation or place stringent limits on them. Even Planck should be able to improve present constraints on defect models by at least an order of magnitude, to the level of $\ep <10^{-7}$. ep="Gv^2$">

The Extraterrestrial Life debate in different cultures
Authors: Jean Schneider (LUTh)
arXiv:1003.0277v1
Surprisingly, the question "Is there Life in the Universe outside Earth?" has been raised, in rational terms, almost only in the western literature throughout the ages. In a first part I justify this statement. Then I try to develop an explanation of this fact by analyzing the different aspects of the notion of decentration.

Probing modifications of General Relativity using current cosmological observations
Authors: Gong-Bo Zhao (1), Tommaso Giannantonio (2), Levon Pogosian (3), Alessandra Silvestri (4), David J. Bacon (1), Kazuya Koyama (1), Robert C. Nichol (1), Yong-Seon Song (1) ((1) ICG Portsmouth, (2) AIfA Bonn, (3) SFU, (4) MIT)
arXiv:1003.0001v1
We test General Relativity (GR) using current cosmological data: the cosmic microwave background (CMB) from WMAP5 (Komatsu et al. 2009), the integrated Sachs-Wolfe (ISW) effect from the cross-correlation of the CMB with six galaxy catalogs (Giannantonio et al. 2008), a compilation of supernovae Type Ia (SNe) including the latest SDSS SNe (Kessler et al. 2009), and part of the weak lensing (WL) data from CFHTLS (Fu et al. 2008, Kilbinger et al. 2009) that probe linear and mildly non-linear scales. We first test a model where the effective Newton's constant, mu, and the ratio of the two gravitational potentials, eta, transit from the GR value to another constant at late times; in this case, we find that standard GR is fully consistent with the combined data. The strongest constraint comes from the ISW effect which would arise from this gravitational transition; the observed ISW signal imposes a tight constraint on a combination of mu and eta that characterizes the lensing potential. Next, we consider four pixels in time and space for each function mu and eta, and perform a Principal Component Analysis (PCA) finding that seven of the resulting eight eigenmodes are consistent with GR within the errors. Only one eigenmode shows a 2-sigma deviation from the GR prediction, which is likely to be due to a systematic effect. However, the detection of such a deviation demonstrates the power of our time- and scale-dependent PCA methodology when combining observations of structure formation and expansion history to test GR.

Multiple Weak Deflections in Galaxy-Galaxy Lensing
Authors: Tereasa G. Brainerd
arXiv:1003.0004v1
The frequency and effects of multiple weak deflections in galaxy-galaxy lensing are investigated via Monte Carlo simulations. The lenses in the simulations are galaxies with known redshifts and known rest-frame blue luminosities. The frequency of multiple deflections above a given threshold shear value is quantified for discrete source redshifts, as well as for a set of sources that are broadly distributed in redshift space. In general, the closest lens in projection on the sky is not the only lens for a given source. In addition, ~50% of the time the closest lens is not the most important lens for a given source. Compared to a naive single-deflection calculation in which only the lensing due to the closest weak lens is considered, a full multiple-deflection calculation yields a higher net shear for individual sources, as well as a higher mean tangential shear around the lens centers. The full multiple-deflection calculation also shows that galaxy-galaxy lensing may contribute a substantial amount to cosmic shear on small angular scales. The degree to which galaxy-galaxy lensing contributes to the small-scale cosmic shear is, however, quite sensitive to the mass adopted for the halos of L_B* galaxies. Changing the halo mass by a factor of ~2.5 changes the contribution of galaxy-galaxy lensing to the cosmic shear by a factor of ~3 on scales of order 1 arcmin. The contribution of galaxy-galaxy lensing to cosmic shear decreases rapidly with angular scale and extrapolates to zero at scales of order 5 arcmin. This last result is roughly independent of the halo mass and suggests that for scales greater than about 5 arcmin, cosmic shear is insensitive to the details of the gravitational potentials of large galaxies.

The Imperatives of Cosmic Biology
Authors: Carl H. Gibson (University of California at San Diego) N. Chandra Wickramasinghe (Cardiff University)
arXiv:1003.0091v1
The transformation of organic molecules into the simplest self-replicating living system,a microorganism, is accomplished from a unique event or rare events that occurred early in the Universe. The subsequent dispersal on cosmic scales and evolution of life is guaranteed, being determined by well-understood processes of physics and biology. Entire galaxies and clusters of galaxies can be considered as connected biospheres, with lateral gene transfers, as initially theorized by Joseph (2000), providing for genetic mixing and Darwinian evolution on a cosmic scale. Big bang cosmology modified by modern fluid mechanics suggests the beginning and wide intergalactic dispersal of life occurred immediately after the end of the plasma epoch when the gas of protogalaxies in clusters fragmented into clumps of planets. Stars are born from binary mergers of such planets within such clumps. When stars devour their surrounding planets to excess they explode, distributing necessary fertilizing chemicals created only in stars with panspermial templates created only in adjacent planets, moons and comets, to be gravitationally collected by the planets and further converted to living organisms. Recent infrared images of nearby star forming regions suggest that life formation on planets like Earth is possible, but not inevitable.

Diffractive Microlensing III: Astrometric Signatures
Authors: Jeremy S. Heyl (UBC)
arXiv:1003.0091v1
The transformation of organic molecules into the simplest self-replicating living system,a microorganism, is accomplished from a unique event or rare events that occurred early in the Universe. The subsequent dispersal on cosmic scales and evolution of life is guaranteed, being determined by well-understood processes of physics and biology. Entire galaxies and clusters of galaxies can be considered as connected biospheres, with lateral gene transfers, as initially theorized by Joseph (2000), providing for genetic mixing and Darwinian evolution on a cosmic scale. Big bang cosmology modified by modern fluid mechanics suggests the beginning and wide intergalactic dispersal of life occurred immediately after the end of the plasma epoch when the gas of protogalaxies in clusters fragmented into clumps of planets. Stars are born from binary mergers of such planets within such clumps. When stars devour their surrounding planets to excess they explode, distributing necessary fertilizing chemicals created only in stars with panspermial templates created only in adjacent planets, moons and comets, to be gravitationally collected by the planets and further converted to living organisms. Recent infrared images of nearby star forming regions suggest that life formation on planets like Earth is possible, but not inevitable.

A New Family of Models for Spherical Stellar Systems
Authors: Natalya Raspopova, Leonid Ossipkov
arXiv:1003.0259v1
A new two-parametric family of mass distribution for spherical stellar systems is considered. It generalizes families by Kuzmin, Veltmann (1972) and by An, Evans (2006). Steady velocity dispersions are found for these models by solving an equation of hydrostatic equilibrium. Axisymmetric generalizations of the model are discussed.

A Numerical Study of Boson Star Binaries
Authors: Bruno C. Mundim
arXiv:1003.0239v1
This thesis describes a numerical study of binary boson stars within the context of an approximation to general relativity. The approximation we adopt places certain restrictions on the dynamical variables of general relativity (conformal flatness of the 3-metric), and on the time-slicing of the spacetime (maximal slicing). The resulting modeling problem requires the solution of a coupled nonlinear system of 4 hyperbolic, and 5 elliptic partial differential equations (PDEs) in three space dimensions and time. We approximately solve this system as an initial-boundary value problem, using finite difference techniques and well known, computationally efficient numerical algorithms such as the multigrid method in the case of the elliptic equations. Careful attention is paid to the issue of code validation, and a key part of the thesis is the demonstration that, as the basic scale of finite difference discretization is reduced, our numerical code generates results that converge to a solution of the continuum system of PDEs as desired. The thesis concludes with a discussion of results from some initial explorations of the orbital dynamics of boson star binaries. In particular, we describe calculations in which motion of such a binary is followed for more than two orbital periods, which is a significant advance over previous studies. We also present results from computations in which the boson stars merge, and where there is evidence for black hole formation.

New Classes of Off-Diagonal Cosmological Solutions in Einstein Gravity
Authors: Sergiu I. Vacaru
arXiv:1003.0043v1
In this work, we apply the anholonomic deformation method for constructing new classes of anisotropic cosmological solutions in Einstein gravity and/or generalizations with nonholonomic variables. There are analyzed four types of, in general, inhomogeneous metrics, defined with respect to anholonomic frames and their main geometric properties. Such spacetimes contain as particular cases certain conformal and/or frame transforms of the well known Friedman--Robertson-Walker, Bianchi, Kasner and Godel universes and define a great variety of cosmological models with generic off-diagonal metrics, local anisotropy and inhomogeneity. It is shown that certain nonholonomic gravitational configurations may mimic de Sitter like inflation scenaria and different anisotropic modifications without satisfying any classical false-vacuum equation of state. Finally, we speculate on perspectives when such off-diagonal solutions can be related to dark energy and dark matter problems in modern cosmology.

arXiv: 1 Mar 2010

Direct reconstruction of dark energy
Authors: Chris Clarkson (Cape Town), Caroline Zunckel (Princeton and KwaZulu-Natal)
arXiv:1002.5004v1
An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With so few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space. We present a new non-parametric method which can accurately reconstruct a wide variety of dark energy behaviour with no prior assumptions about it. It is simple, quick and relatively accurate, and involves no expensive explorations of parameter space. The technique uses principal component analysis and a combination of information criteria to identify real features in the data, and tailors the fitting functions to pick up trends and smooth over noise. We find that we can constrain a large variety of w(z) models to within 10-20 % at redshifts z<1>

Power spectrum of large-scale structure cosmological models in the framework of scalar-tensor theories
Authors: M.A. Rodriguez-Meza
arXiv:1002.4988v1
We study the large-scale structure formation in the Universe in the frame of scalar-tensor theories as an alternative to general relativity. We review briefly the Newtonian limit of non-minimally coupled scalar-tensor theories and the evolution equations of the $N$-body system that is appropriate to study large-scale structure formation in the Universe. We compute the power-spectrum of the universe at present epoch and show how the large-scale structure depends on the scalar field contribution.

Introducing the Dark Energy Universe Simulation Series (DEUSS)
Authors: Y. Rasera, J-M. Alimi, J. Courtin, F. Roy, P-S. Corasaniti, A. Fuzfa, V. Boucher
arXiv:1002.4950v1
In this "Invisible Universe" proceedings, we introduce the Dark Energy Universe Simulation Series (DEUSS) which aim at investigating the imprints of realistic dark energy models on cosmic structure formation. It represents the largest dynamical dark energy simulation suite to date in term of spatial dynamics. We first present the 3 realistic dark energy models (calibrated on latest SNIa and CMB data): LambdaCDM, quintessence with Ratra-Peebles potential, and quintessence with Sugra potential. We then isolate various contributions for non-linear matter power spectra from a series of pre-DEUSS high-resolution simulations (130 million particles). Finally, we introduce DEUSS which consist in 9 Grand Challenge runs with 1 billion particles each thus probing scales from 4 Gpc down to 3 kpc at z=0. Our goal is to make these simulations available to the community through the "Dark Energy Universe Virtual Observatory" (DEUVO), and the "Dark Energy Universe Simulations" (DEUS) consortium.

Habitable Climates: The Influence of Eccentricity
Authors: Courtney D. Dressing (1), David S. Spiegel (1,2), Caleb A. Scharf (3,4), Kristen Menou (2,4), Sean N. Raymond (5,6) ((1) Princeton University (2) Kavli Institute for Theoretical Physics, UCSB, (3) Columbia Astrobiology Center, Columbia Astrophysics Laboratory, (4)Department of Astronomy, Columbia University, (5) Universite Bordeaux, (6) CNRS)
arXiv:1002.4875v1
Radiative equilibrium studies that place Earth-like exoplanets on different circular orbits from the parent star do not fully sample the range of plausible habitability conditions in planetary systems. In the outer regions of the habitable zone, the risk of transitioning into a globally frozen "snowball" state poses a threat to the habitability. Here, we use a one-dimensional energy balance climate model (EBM) to examine how obliquity, spin rate, orbital eccentricity, and the fraction of the surface covered by ocean might influence the onset of such a snowball state. Since, for constant semimajor axis, the annual mean stellar irradiation scales with (1-e^2)^(-1/2), one might expect the greatest habitable semimajor axis to scale as (1-e^2)^(-1/4). We find that this standard simple ansatz provides a reasonable lower bound on the outer boundary of the habitable zone, but the influence of both obliquity and ocean fraction can be profound in the context of planets on eccentric orbits. For planets with eccentricity 0.5, our EBM suggests that the greatest habitable semimajor axis can vary by more than 0.8 AU (78%!) depending on obliquity, with higher obliquity worlds generally more stable against snowball transitions. One might also expect that the long winter at an eccentric planet's apoastron would render it more susceptible to global freezing. Our models suggest that this is not a significant risk for Earth-like planets around Sun-like stars, as considered here, since such planets are buffered by the thermal inertia provided by oceans covering at least 10% of their surface. Nevertheless, the extreme temperature variations achieved on highly eccentric exo-Earths raise questions about the adaptability of life to marginally or transiently habitable conditions.

f(R) theories
Authors: Antonio De Felice, Shinji Tsujikawa
136 pages, 14 figures, Invited review article in Living Reviews in Relativity, Comments are welcome
arXiv:1002.4928v1
Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity--such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory, Gauss-Bonnet gravity, extra dimensional models, Galileon theory, and address models that can satisfy both cosmological and local gravity constraints.

arXiv: 26 Feb 2010

Applicability of the linearly perturbed FRW metric and Newtonian cosmology
Authors: Syksy Rasanen
arXiv:1002.4779v1
It has been argued that the effect of cosmological structure formation on the average expansion rate is negligible, because the linear approximation to the metric remains applicable in the regime of non-linear density perturbations. We discuss why the arguments based on the linear theory are not valid. We emphasise the difference between Newtonian gravity and the weak field, small velocity limit of general relativity in the cosmological setting.

Companion stars of Type Ia supernovae and single low-mass white dwarfs
Authors: Bo Wang, Zhanwen Han
arXiv:1002.4742v1
Recent investigations of the WD + MS channel of Type Ia supernovae (SNe Ia) imply that this channel may be the main contribution to the old population (>1Gyr) of SNe Ia. In the WD + MS channel, the WD could accrete material from a main-sequence or a slightly evolved star until it reaches the Chandrasekhar mass limit. The companions in this channel would survive after SN explosion and show distinguishing properties. In this Letter, based on SN Ia production regions of the WD + MS channel and three formation channels of WD + MS systems, we performed a detailed binary population synthesis study to obtain the properties of the surviving companions. The properties can be verified by future observations. We find that the surviving companions of the old SNe Ia have a low mass, which provides a possible way to explain the formation of the population of single low-mass WDs (<0.45msun).

Measuring Unified Dark Matter with 3D cosmic shear
Authors: Stefano Camera, Thomas D. Kitching, Alan F. Heavens, Daniele Bertacca, Antonaldo Diaferio
arXiv:1002.4740v1
We present parameter estimation forecasts for future 3D cosmic shear surveys for a class of Unified Dark Matter (UDM) models, where a single scalar field mimics both Dark Matter (DM) and Dark Energy (DE). These models have the advantage that they can describe the dynamics of the Universe with a single matter component providing an explanation for structure formation and cosmic acceleration. A crucial feature of the class of UDM models we use in this work is characterized by a parameter, c_inf (c=1), that is the value of the sound speed at late times and on which structure formation depends. We demonstrate that the properties of the DM-like behaviour of the scalar field can be estimated with very high precision with large-scale, fully 3D weak lensing surveys. We found that 3D weak lensing significantly constrains c_inf, and we find minimal errors 0.00013, for the fiducial value c_inf=0.0005, and 0.0004, for c_inf=0.05. Moreover, we compute the Bayesian evidence for UDM models over the LCDM model as a function of c_inf. For this purpose, we can consider the LCDM model as a UDM model with c_inf=0. We find an interesting maximum in the Bayes factor. This is due to the peculiar dynamics of UDM models. In fact, as the value of c_inf increases, its signature in the shear signal becomes more and more evident, until the sound speed is so high that the DM-like component of the scalar field can not cluster any more, thus the shear signal starts to be damped and the evidence decreases. Moreover, the expected evidence clearly shows that the survey data would unquestionably favour UDM models over the LCDM model, if c_inf>0.0001.

The Abnormally Weighting Energy Hypothesis: The origin of the cosmic acceleration
Authors: J.-M. Alimi, A. Fuzfa
arXiv:1002.4721v1
We generalize tensor-scalar theories of gravitation by the introduction of an abnormally weighting type of energy. This theory of tensor-scalar anomalous gravity is based on a relaxation of the weak equivalence principle that is now restricted to ordinary visible matter only. As a consequence, the convergence mechanism toward general relativity is modified and produces naturally cosmic acceleration as an inescapable gravitational feedback induced by the mass-variation of some invisible sector. The cosmological implications of this new theoretical framework are studied. This glimpses at an enticing new symmetry between the visible and invisible sectors, namely that the scalar charges of visible and invisible matter are exactly opposite.

Dark Matter and Dark Energy from Gravitational Symmetry Breaking
Authors: A. Fuzfa, J.-M. Alimi
arXiv:1002.4715v1
We build a mechanism of gravitational symmetry breaking (GSB) of a global U(1) symmetry based on the relaxation of the equivalence principle due to the mass variation of pseudo Nambu-Goldstone dark matter (DM) particles. This GSB process is described by the modified cosmological convergence mechanism of the Abnormally Weighting Energy (AWE) Hypothesis previously introduced by the authors. Several remarkable constraints from the Hubble diagram of far-away supernovae are derived, notably on the explicit and gravitational symmetry breaking energy scales of the model. We then briefly present some consequences on neutrino masses when this mechanism is applied to the particular case of the breaking of lepton number symmetry.

The Spitzer search for the transits of HARPS low-mass planets - I. No transit for the super-Earth HD 40307b
Authors: M. Gillon (1,2), D. Deming (3), B.-O. Demory (4,2), C. Lovis (2), S. Seager (4), M. Mayor (2), F. Pepe (2), D. Queloz (2), D. Segransan (2), S. Udry (2), S. Delmelle (1), P. Magain (1) ((1) University of Liege, Belgium, (2) Geneva Observatory, Switzerland, (3) NASA/Goddard SFC, Greenbelt, USA, (4) MIT, Boston, USA)
arXiv:1002.4707v1
We have used Spitzer and its IRAC camera to search for the transit of the super-Earth HD 40307b. The transiting nature of the planet could not be firmly discarded from our first photometric monitoring of a transit window because of the uncertainty coming from the modeling of the photometric baseline. To obtain a firm result, two more transit windows were observed and a global Bayesian analysis of the three IRAC time series and the HARPS radial velocities was performed. Unfortunately, any transit of the planet during the observed phase window is firmly discarded, while the probability that the planet transits but that the eclipse was missed by our observations is nearly negligible (0.26%).

Educated search for transiting habitable planets. Targetting M dwarfs with known transiting planets
Authors: M. Gillon (1,2), X. Bonfils (2,3), B.-O. Demory (4,2), S. Seager (4), D. Deming (5) ((1) University of Liege, Belgium, (2) Geneva Observatory, Switzerland, (3) University Joseph-Fourier, Grenoble, France, (4) MIT, Boston, USA, (5) NASA/Goddard SFC, Greenbelt, USA)
arXiv:1002.4702v1
Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. Depending on several parameters, significantly enhanced transit probability could be expected for habitable planets. This approach is especially interesting for M dwarfs because these stars have close-in habitable zones and because their small radii make possible the detection of terrestrial planets down to Mars size. We investigate the potential of this approach for the two M dwarfs known to host a transiting planet, GJ 436 and GJ 1214. Contrary to GJ 436, GJ 1214 reveals to be a very promising target for the considered approach. Assuming a distribution of orbital inclinations similar to our solar system, a habitable planet orbiting around GJ 1214 would have a mean transit probability of ~25%, much better than the probability of 1.5% expected if the transits of GJ 1214b are not considered. Because of the small size of GJ 1214, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring (e.g., with Warm Spitzer) could detect any transiting habitable planet down to the size of Mars. A dedicated high-precision photometric monitoring of M dwarfs known to harbor close-in transiting planets could thus be an efficient way to detect transiting habitable planets much smaller than our Earth that would be out of reach for existing Doppler and transit surveys.