arXiv: 20 September 2010

Cosmological and Solar-System Tests of f(R) Modified Gravity

Authors: Wei-Ting Lin, Je-An Gu, Pisin Chen

http://arxiv.org/abs/1009.3488v1

We investigate the cosmological and the local tests of the f(R) theory of modified gravity via the observations of (1) the cosmic expansion and (2) the cosmic structures and via (3) the solar-system experiments. To fit the possible cosmic expansion histories under consideration, for each of them we reconstruct f(R), known as "designer f(R)". We then test the designer f(R) via the cosmic-structure constraints on the metric perturbation ratio Psi/Phi and the effective gravitational coupling G_eff and via the solar-system constraints on the Brans-Dicke theory with the chameleon mechanism. We find that among the designer f(R) models specified by the CPL effective equation of state w_eff, only the model closely mimicking general relativity with a cosmological constant (LambdaCDM) can survive all the tests. Accordingly, these tests rule out the frequently studied "w_eff = -1" designer f(R) models which are distinct in cosmic structures from LambdaCDM. When considering only the cosmological tests, we find that the surviving designer f(R) models, although exist for a variety of w_eff, entail fine-tuning.

The Weak Field Limit of Fourth Order Gravity

Authors: Salvatore Capozziello, Arturo Stabile

http://arxiv.org/abs/1009.3441v1

We discuss Newtonian and the post-Newtonian limits of Fourth Order Gravity Theories pointing out, in details, their resemblances and differences with respect to General Relativity. Particular emphasis is placed on the exact solutions and methods used to obtain them.

 

Figures of Merit for Testing Standard Models: Application to Dark Energy Experiments in Cosmology

Authors: Adam Amara, Thomas Kitching

http://arxiv.org/abs/1009.3274v1

Given a standard model to test, an experiment can be designed to: (i) measure the standard model parameters; (ii) extend the standard model; or (iii) look for evidence of deviations from the standard model. To measure (or extend) the standard model, the Fisher matrix is widely used in cosmology to predict expected parameter errors for future surveys under Gaussian assumptions. In this article, we present a frame- work that can be used to design experiments such that it maximises the chance of finding a deviation from the standard model. Using a simple illustrative example, discussed in the appendix, we show that the optimal experimental configuration can depend dramatically on the optimisation approach chosen. We also show some simple cosmology calculations, where we study Baryonic Acoustic Oscillation and Supernove surveys. In doing so, we also show how external data, such as the positions of the CMB peaks measured by WMAP, and theory priors can be included in the analysis. In the cosmological cases that we have studied (DETF Stage III), we find that the three optimisation approaches yield similar results, which is reassuring and indicates that the choice of optimal experiment is fairly robust at this level. However, this may not be the case as we move to more ambitious future surveys.

 

Scale dependence of $f_{NL}$ in N-flation

Authors: Qing-Guo Huang

http://arxiv.org/abs/1009.3326v1

Adopting the horizon-crossing approximation, we derive the spectral index of $f_{NL}$ in general N-flation model. Axion N-flation model is a typical model for generating a large $f_{NL}$, but its tilt $n_{f_{NL}}$ is too small to be detected when all fields have the same potential. The measurement of $n_{f_{NL}}$ can be used to support or falsify the axion N-flation in the near future.

 

Dark haloes as seen with gravitational lensing

Authors: Konrad Kuijken

http://arxiv.org/abs/1009.3405v1

Dark matter is an important ingredient of galaxies, as was recognised early on by Ken Freeman himself! Evidence for dark matter halos is still indirect, based on analysing motions of tracers such as gas and stars. In a sense the visible galaxy is the mask through which we can study the dark matter. Light rays are also sensitive to gravitational fields, and dark haloes cause observable gravitational lensing effects. There are three regimes: microlensing (which probes the clumpiness of dark matter haloes), strong lensing (sensitive to the inner mass distribution) and weak lensing (which can probe haloes out to 100s of kpc from the center). This review will concentrate on weak lensing, and describe a new survey, the Kilo-Degree Survey (KiDS) that is designed to study galaxy halo masses, extents and shapes as a function of environment, galaxy type and redshift

 

Modeling scale-dependent bias on the baryonic acoustic scale with the statistics of peaks of Gaussian random fields

Authors: Vincent Desjacques, Martin Crocce, Roman Scoccimarro, Ravi K. Sheth

http://arxiv.org/abs/1009.3449v1

Models of galaxy and halo clustering commonly assume that the tracers can be treated as a continuous field locally biased with respect to the underlying mass distribution. In the peak model pioneered by BBKS, one considers instead density maxima of the initial, Gaussian mass density field as an approximation to the formation site of virialized objects. In this paper, the peak model is extended in two ways to improve its predictive accuracy. Firstly, we derive the two-point correlation function of initial density peaks up to second order and demonstrate that a peak-background split approach can be applied to obtain the k-independent and k-dependent peak bias factors at all orders. Secondly, we explore the gravitational evolution of the peak correlation function within the Zel'dovich approximation. We show that the local (Lagrangian) bias approach emerges as a special case of the peak model, in which all bias parameters are scale-independent and there is no statistical velocity bias. We apply our formulae to study how the Lagrangian peak biasing, the diffusion due to large scale flows and the mode-coupling due to nonlocal interactions affect the scale dependence of bias from small separations up to the baryon acoustic oscillation (BAO) scale. For 2-sigma density peaks collapsing at z=0.3, our model predicts a ~ 5% residual scale-dependent bias around the acoustic scale that arises mostly from first-order Lagrangian peak biasing (as opposed to second-order gravity mode-coupling). We also search for a scale dependence of bias in the large scale auto-correlation of massive halos extracted from a very large N-body simulation provided by the MICE collaboration. For halos with mass M>10^{14}Msun/h, our measurements demonstrate a scale-dependent bias across the BAO feature which is very well reproduced by a prediction based on the peak model.

 

 

 

 

arXiv: 17 September 2010

Probing dark energy and neutrino mass from upcoming lensing experiments of CMB and galaxies

Authors: Toshiya Namikawa, Shun Saito, Taruya Atsushi

http://arxiv.org/abs/1009.3204v1

We discuss the synergy of the cosmic shear and CMB lensing experiments to simultaneously constrain the neutrino mass and dark energy properties. Taking fully account of the CMB lensing, cosmic shear, CMB anisotropies, and their cross correlation signals, we clarify a role of each signal, and investigate the extent to which the upcoming observations by a high-angular resolution experiment of CMB and deep galaxy imaging survey can tightly constrain the neutrino mass and dark energy equation-of-state parameters. Including the primary CMB information as a prior cosmological information, the Fisher analysis reveals that the time varying equation-of-state parameters, given by $w(a)=w_0+w_a(1-a)$, can be tightly constrained with the accuracies of 5% for $w_0$ and 15% for $w_a$, which are comparable to or even better than those of the stage-III type surveys neglecting the effect of massive neutrinos. In other words, including the neutrino mass in the parameter estimation would not drastically alter the Figure-of-Merit estimates of dark energy parameters from the weak lensing measurements. For the neutrino mass, a clear signal for total neutrino mass with $\sim0.1$\,eV can be detected with $\sim2$-$\sigma$ significance. The robustness and sensitivity of these results are checked in detail by allowing the setup of cosmic shear experiment to vary as a function of observation time or exposure time, showing that the improvement of the constraints very weakly depends on the survey parameters, and the results mentioned above are nearly optimal for the dark energy parameters and the neutrino mass.

 

Precision cosmology with a wide area XMM cluster survey

Authors: M. Pierre, F. Pacaud, J.B. Juin, J.B. Melin, N. Clerc, P.S. Corasaniti

http://arxiv.org/abs/1009.3182v1

We explore the cosmological constraints expected from wide area XMM-type cluster surveys covering 50-200 deg2, under realistic observing conditions. We perform a Fisher matrix analysis based on cluster number counts in combination with estimates of the 2-point cluster correlation function. The effect of the survey design is implemented through an observationally well tested cluster selection function. Special attention is given to the modelling of the shot noise and sample variance, which we estimate by applying our selection function to numerically simulated surveys. We then infer the constraints on the equation of state of the dark energy considering various survey configurations. We quantitatively investigate the respective impact of the cluster mass measurements, of the correlation function and of the 1<z<2 cluster population. We show that, with some 20 Ms XMM observing time, it is possible to constrain the dark energy parameters at a level which is comparable to that expected from the next generation of cosmic probes. Such a survey has also the power to provide unique insights into the physics of high redshift clusters and AGN properties.

 

Estimate of dark halo ellipticity by lensing flexion

Authors: Xinzhong Er (AIfA & IMPRS Bonn), Peter Schneider (AIfA Bonn)

http://arxiv.org/abs/1009.3125v1

Aims. The predictions of the ellipticity of the dark matter halos from models of structure formation are notoriously difficult to test with observations. A direct measurement would give important constraints on the formation of galaxies, and its effect on the dark matter distribution in their halos. Here we show that galaxy-galaxy flexion provides a direct and potentially powerful method for determining the ellipticity of (an ensemble of) elliptical lenses. Methods. We decompose the spin-1 flexion into a radial and a tangential component. Using the ratio of tangential-to- radial flexion, which is independent of the radial mass profile, the mass ellipticity can be estimated. Results. An estimator for the ellipticity of the mass distribution is derived and tested with simulations. We show that the estimator is slightly biased. We quantify this bias, and provide a method to reduce it. Furthermore, a parametric fitting of the flexion ratio and orientation provides another estimate for the dark halo ellipticity, which is more accurate for individual lenses Overall, galaxy-galaxy flexion appears as a powerful tool for constraining the ellipticity of mass distributions. Aims. The predictions of the ellipticity of the dark matter halos from models of structure formation are notoriously difficult to test with observations. A direct measurement would give important constraints on the formation of galaxies, and its effect on the dark matter distribution in their halos. Here we show that galaxy-galaxy flexion provides a direct and potentially powerful method for determining the ellipticity of (an ensemble of) elliptical lenses. Methods. We decompose the spin-1 flexion into a radial and a tangential component. Using the ratio of tangential-to- radial flexion, which is independent of the radial mass profile, the mass ellipticity can be estimated. Results. An estimator for the ellipticity of the mass distribution is derived and tested with simulations. We show that the estimator is slightly biased. We quantify this bias, and provide a method to reduce it. Furthermore, a parametric fitting of the flexion ratio and orientation provides another estimate for the dark halo ellipticity, which is more accurate for individual lenses Overall, galaxy-galaxy flexion appears as a powerful tool for constraining the ellipticity of mass distributions.

Strongly Scale-dependent Non-Gaussianity

Authors: Antonio Riotto, Martin S. Sloth

http://arxiv.org/abs/1009.3020v1

We discuss models of primordial density perturbations where the non-Gaussianity is strongly scale-dependent. In particular, the non-Gaussianity may have a sharp cut-off and be very suppressed on large cosmological scales, but sizeable on small scales. This may have an impact on probes of non-Gaussianity in the large-scale structure and in the cosmic microwave background radiation anisotropies.

 

General Relativistic Description of the Observed Galaxy Power Spectrum: Do We Understand What We Measure?

Authors: Jaiyul Yoo (Harvard/Zürich)

http://arxiv.org/abs/1009.3021v1

We extend the general relativistic description of galaxy clustering developed in Yoo, Fitzpatrick, and Zaldarriaga (2009). For the first time we provide a fully general relativistic description of the observed matter power spectrum and the observed galaxy power spectrum with the linear bias ansatz. It is significantly different from the standard Newtonian description on large scales and especially its measurements on large scales can be misinterpreted as the detection of the primordial non-Gaussianity even in the absence thereof. The key difference in the observed galaxy power spectrum arises from the real-space matter fluctuation defined as the matter fluctuation at the hypersurface of the observed redshift. As opposed to the standard description, the shape of the observed galaxy power spectrum evolves in redshift, providing additional cosmological information. While the systematic errors in the standard Newtonian description are negligible in the current galaxy surveys at low redshift, correct general relativistic description is essential for understanding the galaxy power spectrum measurements on large scales in future surveys with redshift depth z>3. We discuss ways to improve the detection significance in the current galaxy surveys and comment on applications of our general relativistic formalism in future surveys.

 

 

arXiv: 16 September 2010

Coherent Combination of BAO and Peculiar Velocity Measurements from Redshift Survey

Authors: Yong-Seon Song (KIAS, Korea Institute for Advanced Study)

http://arxiv.org/abs/1009.2753v1

New statistical method is proposed to coherently combine Baryon Acoustic Oscillation statistics (BAO) and peculiar velocity measurements exploiting decomposed density--density and velocity-velocity spectra in real space from the observed redshift distortions in redshift space, 1) to achieve stronger dark energy constraints, sigma(w)=0.06 and sigma(w_a)=0.20, which are enhanced from BAO or velocity measurements alone, and 2) to cross-check consistency of dark energy constraints from two different approaches; BAO as geometrical measurements and peculiar velocity as large scale structure formation observables. In addition to those advantages, as power spectra decomposition procedure is free from uncertainty of galaxy bias, this simultaneous fitting is an optimal method to extract cosmological parameters without any pre-assumption about galaxy bias.

 

 

arXiv: 15 September 2010

Are Galaxy Clusters Suggesting an Accelerating Universe?

Authors: J. A. S. Lima, R. F. L. Holanda, J. V. Cunha

http://arxiv.org/abs/1009.2736v1

The present cosmic accelerating stage is discussed through a new kinematic method based on the Sunyaev- Zel'dovich effect (SZE) and X-ray surface brightness data from galaxy clusters. By using the SZE/X-ray data from 38 galaxy clusters in the redshift range $0.14 \leq z \leq 0.89 $ [Bonamente et al., Astrop. J. {\bf 647}, 25 (2006)] it is found that the present Universe is accelerating and that the transition from an earlier decelerating to a late time accelerating regime is relatively recent. The ability of the ongoing Planck satellite mission to obtain tighter constraints on the expansion history through SZE/X-ray angular diameters is also discussed. Our results are fully independent on the validity of any metric gravity theory, the possible matter- energy contents filling the Universe, as well as on the SNe Ia Hubble diagram from which the presenting accelerating stage was inferred.

 

Current constraints on the epoch of cosmic acceleration

Authors: B. Santos, J.C. Carvalho, J.S. Alcaniz

http://arxiv.org/abs/1009.2733v1

The cosmographic expansion history of the universe is investigated by using the 557 type Ia supernovae from the Union2 Compilation set along with the current estimates involving the product of the CMB acoustic scale $\ell_{A}$ and the BAO peak at two different redshifts. Using a well-behaved parameterization for the deceleration parameter, $q(z) = q_0 + q_1z/(1 + z)$, we estimate the accelerating redshift $z_{acc}=-q_0/(q_0 + q_1)$ (at which the universe switches from deceleration to acceleration) and investigate the influence of a non-vanishing spatial curvature on these estimates. We also use the asymptotic value of $q(z)$ at high-$z$ to place more restrictive bounds on the model parameters $q_0$ and $q_1$, which results in a more precise determination of the epoch of cosmic acceleration.

 

Correspondence between Jordan-Einstein frames and Palatini-metric formalisms

Authors: Salvatore Capozziello, Farhad Darabi, Daniele Vernieri

http://arxiv.org/abs/1009.2580v1

We discuss the conformal symmetry between Jordan and Einstein frames considering their relations with the metric and Palatini formalisms for modified gravity. Appropriate conformal transformations are taken into account leading to the evident connection between the gravitational actions in the two mentioned frames and the Hilbert-Einstein action with a cosmological constant. We show that the apparent differences between Palatini and metric formalisms strictly depend on the representation while the number of degrees of freedom is preserved. This means that the dynamical content of both formalism is identical.

 

Eternal inflation without metaphysics

Authors: James Hartle, S.W. Hawking, Thomas Hertog

http://arxiv.org/abs/1009.2525v1

In the usual account of eternal inflation the universe is supposed to be a de Sitter background in which pocket universes nucleate at a steady rate. However this is metaphysics because there is no way this mosaic structure can be observed. We don't see the whole universe but only a nearly homogeneous region within our past light cone. We show that we can use the no-boundary wave function to calculate small departures from homogeneity within our past light cone despite the possibility of much larger fluctuations on super horizon scales. We find that the dominant contribution comes from the history that exits eternal inflation at the lowest value of the potential and predict, in a certain class of landscape models, a tensor to scalar ratio of about 10%. In this way the no-boundary wave function defines a measure for the prediction of local cosmological observations

 

An equivalence principle for scalar forces

Authors: Lam Hui, Alberto Nicolis

http://arxiv.org/abs/1009.2520v1

The equivalence of inertial and gravitational masses is a defining feature of general relativity. Here, we clarify the status of the equivalence principle for interactions mediated by a universally coupled scalar, motivated partly by recent attempts to modify gravity at cosmological distances. Although a universal scalar-matter coupling is not mandatory, once postulated, it is stable against classical and quantum renormalizations in the matter sector. The coupling strength itself is subject to renormalization of course. The scalar equivalence principle is violated only for objects for which either the graviton self-interaction or the scalar self-interaction is important---the first applies to black holes, while the second type of violation is avoided if the scalar is Galilean-symmetric.

 

Galileon inflation

Authors: Clare Burrage, Claudia de Rham, David Seery, Andrew J. Tolley

http://arxiv.org/abs/1009.2497v1

Galileon inflation is a radiatively stable higher derivative model of inflation. The model is determined by a finite number of relevant operators which are protected by a covariant generalization of the Galileon shift symmetry. We show that the nongaussianity of the primordial density perturbation generated during an epoch of Galileon inflation is a particularly powerful observational probe of these models and that, when the speed of sound is small, fNL can be larger than the usual result fNL ~ 1/c_s^2.

 

 

arXiv: 14 September 2010

Neutrino lumps and the Cosmic Microwave Background

Authors: Valeria Pettorino, Nico Wintergerst, Luca Amendola, Christof Wetterich

http://arxiv.org/abs/1009.2461v1

The interaction between the cosmon and neutrinos may solve the "why now problem" for dark energy cosmologies. Within growing neutrino quintessence it leads to the formation of nonlinear neutrino lumps. For a test of such models by the integrated Sachs-Wolfe effect for the cosmic microwave background (CMB) we estimate the size and time evolution of the gravitational potential induced by these lumps. A population of lumps with size of 100 Mpc or more could lead to observable effects on the CMB anisotropies for low angular momenta. The linear approximation is found to be invalid for the relevant length scales. Quantitative estimates depend strongly on the details of the transition between the linear and nonlinear regimes. In particular, important backreaction effects arise from the nonlinearities of the cosmon interactions. At the present stage the uncertainties of the estimate make it difficult to constrain the parameter space of growing neutrino models. We explicitly discuss scenarios and models that are compatible with the CMB observations

 

Effect of dark matter halo substructures on galaxy rotation curves

Authors: Nirupam Roy

http://arxiv.org/abs/1009.2099v1

The effect of halo substructures on galaxy rotation curves is investigated in this paper using a simple model of dark matter clustering. A dark matter halo density profile is developed based only on the scale free nature of clustering that leads to a statistically self-similar distribution of the substructures at galactic scale. Semi-analytical method is used to derive rotation curves for such a clumpy dark matter density profile. It is found that the halo substructures significantly affect the galaxy velocity field. Based on the fractal geometry of the halo, this self-consistent model predicts an NFW-like rotation curve and a scale free power spectrum of the rotation velocity fluctuations.

 

The Effective Field Theory of Multifield Inflation

Authors: Leonardo Senatore, Matias Zaldarriaga

http://arxiv.org/abs/1009.2093v1

We generalize the Effective Field Theory of Inflation to include additional light scalar degrees of freedom that are in their vacuum at the time the modes of interest are crossing the horizon. In order to make the scalars light in a natural way we consider the case where they are the Goldstone bosons of a global symmetry group or are partially protected by an approximate supersymmetry. We write the most general Lagrangian that couples the scalar mode associated to the breaking of time translation during inflation to the additional light scalar fields. This Lagrangian is constrained by diffeomorphism invariance and the additional symmetries that keep the new scalars light. This Lagrangian describes the fluctuations around the time of horizon crossing and it is supplemented with a general parameterization describing how the additional fluctuating fields can affect cosmological perturbations. We find that multifield inflation can reproduce the non-Gaussianities that can be generated in single field inflation but can also give rise to new kinds of non-Gaussianities. We find several new three-point function shapes. We show that in multifield inflation it is possible to naturally suppress the three-point function making the four-point function the leading source of detectable non-Gaussianities. We find that under certain circumstances, i.e. if specific shapes of non-Gaussianities are detected in the data, one could distinguish between single and multifield inflation and sometimes even among the various mechanisms that kept the additional fields light.

 

arXiv: 13 September 2010

Theory of Dark Matter

Authors: Graciela B Gelmini
http://arxiv.org/abs/1009.1942v1

The search for dark matter is a very wide and active field of research. Many potential hints of dark matter have appeared recently which led to a burst of theoretical activity and model building. I necessarily concentrate here only in some aspects of it. I review here some recent hints and some of the ways in which they could be explained.

 

Characterizing the contaminating distance distribution for Bayesian supernova cosmology

Authors: Bridget L. Falck, Adam G. Riess, Renee Hlozek

http://arxiv.org/abs/1009.1903v1

Measurements of the equation of state of dark energy from surveys of thousands of Type Ia Supernovae (SNe Ia) will be limited by spectroscopic follow-up and must therefore rely on photometric identification, increasing the chance that the sample is contaminated by Core Collapse Supernovae (CC SNe). Bayesian methods for supernova cosmology can remove contamination bias while maintaining high statistical precision but are sensitive to the choice of parameterization of the contaminating distance distribution. We use simulations to investigate the form of the contaminating distribution and its dependence on the absolute magnitudes, light curve shapes, colors, extinction, and redshifts of core collapse supernovae. We find that the CC luminosity function dominates the distance distribution function, but its shape is increasingly distorted as the redshift increases and more CC SNe fall below the survey magnitude limit. The shapes and colors of the CC light curves generally shift the distance distribution, and their effect on the CC distances is correlated. We compare the simulated distances to the first year results of the SDSS-II SN survey and find that the SDSS distance distributions can be reproduced with simulated CC SNe that are ~1 mag fainter than the standard Richardson et al. (2002) luminosity functions, which do not produce a good fit. To exploit the full power of the Bayesian parameter estimation method, parameterization of the contaminating distribution should be guided by the current knowledge of the CC luminosity functions, coupled with the effects of the survey selection and magnitude-limit, and allow for systematic shifts caused by the parameters of the distance fit.

 

Density fields and halo mass functions in the Geometrical Adhesion toy Model

Authors: Patrick Valageas, Francis Bernardeau

http://arxiv.org/abs/1009.1974v1

In dimension 2 and above, the Burgers dynamics, the so-called "adhesion model" in cosmology, can actually give rise to several dynamics in the inviscid limit. We investigate here the statistical properties of the density field when it is defined by a "geometrical model' associated with this Burgers velocity field and where the matter distribution is fully determined, at each time step, by geometrical constructions. Our investigations are based on a set of numerical experiments that make use of an improved algorithm, for which the geometrical constructions are efficient and robust.
In this work we focus on Gaussian initial conditions with power-law power spectra of slope $n$ in the range $-3<n<1$, where a self-similar evolution develops, and we compute the behavior of power spectra, density probability distributions and mass functions. As expected for such dynamics, the density power spectra show universal high-$k$ tails that are governed by the formation of pointlike masses. The two other statistical indicators however show the same qualitative properties as those observed for 3D gravitational clustering. In particular, the mass functions obey a Press-Schechter like scaling up to a very good accuracy in 1D, and to a lesser extent in 2D.
Our results suggest that the "geometrical adhesion model" whose solution is fully known at all times, provides a precious tool to understand some of the statistical constructions frequently used to study the development of mass halos in gravitational clustering.

 

 

arXiv: 10 September 2010

Quantum Fluctuations of Vector Fields and the Primordial Curvature Perturbation in the Universe

Authors: Mindaugas Karciauskas

http://arxiv.org/abs/1009.1779v1

PhD thesis, 183 pages, 16 figures
The \delta N formalism is extended to include the perturbation of the vector field. The latter is quantized in de Sitter space-time and it is found that in general the particle production process of the vector field is anisotropic. This anisotropy is parametrized by introducing two parameters p and q, which are determined by the conformal invariance breaking mechanism. If any of them are non-zero, generated \zeta is statistically anisotropic. Then the power spectrum of \zeta and the non-linearity parameter fNL have an angular modulation. This formalism is applied for two vector curvaton models and the end-of-inflation scenario. It is found that for p \ne 0, the magnitude of fNL and the direction of its angular modulation is correlated with the anisotropy in the spectrum. If p \gtrsim 1, the anisotropic part of fNL is dominant over the isotropic one. These are distinct observational signatures; their detection would be a smoking gun for a vector field contribution to \zeta . In the first curvaton model the vector field is non-minimally coupled to gravity and in the second one it has a time varying kinetic function and mass. In the former, only statistically anisotropic \zeta can be generated, while in the latter, isotropic \zeta may be realized too. Parameter spaces for these vector curvaton scenarios are large enough for them to be realized in the particle physics models. In the end-of-inflation scenario fNL have similar properties to the vector curvaton scenario with additional anisotropic term.

 

First life in primordial-planet oceans: the biological big bang

Authors: Carl H. Gibson (Univ. Cal. San Diego US) N. Chandra Wickramasinghe (Cardiff Univ. UK) Rudolph E. Schild (Harvard Univ. US)

http://arxiv.org/abs/1009.1760v1

A scenario is presented for the formation of first life in the universe based on hydro-gravitational-dynamics (HGD) cosmology. From HGD, the dark matter of galaxies is H-He gas dominated planets (primordial-fog-particle PFPs) in million solar mass clumps (protoglobularstarcluster PGCs), which formed at the plasma to gas transition temperature 3000 K. Stars result from mergers of the hot-gas-planets. Over-accretion causes stars to explode as supernovae that scatter life-chemicals (C, N, O, P, S, Ca, Fe etc.) to other planets in PGC clumps and beyond. These chemicals were first collected gravitationally by merging PFPs to form H-saturated, high-pressure, dense oceans of critical-temperature 647 K water over iron-nickel cores at ~ 2 Myr. Stardust fertilizes the formation of first life in a cosmic hot-ocean soup kitchen comprised of all planets and their moons in meteoric communication, > 10^100 kg in total. Ocean freezing slows this biological big bang at ~ 8 Myr. HGD cosmology confirms that the evolving seeds of life are scattered on intergalactic scales by Hoyle-Wickramasinghe cometary panspermia. Thus, life flourishes on planets like Earth that would otherwise be sterile.

 

Brane-World Gravity

Authors: Roy Maartens (ICG, Portsmouth), Kazuya Koyama (ICG, Portsmouth)

http://arxiv.org/abs/1004.3962v2

The observable universe could be a 1+3-surface (the "brane") embedded in a 1+3+\textit{d}-dimensional spacetime (the "bulk"), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the \textit{d} extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak ($\sim$ TeV) level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes, and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review analyzes the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall--Sundrum models. We also cover the simplest brane-world models in which 4-dimensional gravity on the brane is modified at \emph{low} energies -- the 5-dimensional Dvali--Gabadadze--Porrati models. Then we discuss co-dimension two branes in 6-dimensional models.

arXiv: 9 September 2010

Scale-Dependent Bias of Galaxies from Baryonic Acoustic Oscillations

Authors: Rennan Barkana (Tel Aviv University), Abraham Loeb (Harvard University)

http://arxiv.org/abs/1009.1393v1

Baryonic acoustic oscillations (BAOs) modulate the density ratio of baryons to dark matter across large regions of the Universe. We show that the associated variation in the mass-to-light ratio of galaxies should generate an oscillatory, scale-dependent bias of galaxies relative to the underlying distribution of dark matter. A measurement of this effect would calibrate the dependence of the characteristic mass-to-light ratio of galaxies on the baryon mass fraction in their large scale environment. This bias, though, is unlikely to significantly affect measurements of BAO peak positions.

 

Unification of Dark Matter and Dark Energy in a Modified Entropic Force Model

Authors: Zhe Chang, Ming-Hua Li, Xin Li

http://arxiv.org/abs/1009.1506v1

In Verlinde's entropic force scenario of gravity, Newton's laws and Einstein equations can be obtained from the first pinciples and general assumptions. However, the equipartition law of energy is invalid at very low temperatures. We show clearly that the threshold of the equipartition law of energy is related with horizon of the universe. Thus, a one-dimension Debye (ODD) model in the direction of radius of the modified entropic force (MEF) maybe suitable in description of the accelerated expanding universe. We present a Friedmann cosmic dynamical model in the ODD-MEF framework. We examine carefully constraints on the ODD-MEF model from the Union2 compilation of the Supernova Cosmology Project (SCP) collaboration, the data from the observation of the large-scale structure (LSS) and the cosmic microwave background (CMB), i.e. SNe Ia+LSS+CMB. The combined numerical analysis gives the best-fit value of the model parameters $\zeta\simeq10^{-9}$ and $\Omega_{m0}=0.224$, with $\chi_{min}^2=591.156$. The corresponding age of the universe agrees with the result of D. Spergel {\it et al.}\cite{Spergel2003} at 95% confidence level. The numerical result also yields an accelerated expanding universe without invoking any kind of dark energy. Taking $\zeta(\equiv 2\pi \omega_D/H_0)$ as a running parameter associated with the structure scale $r$, we obtain a possible unified scenario of the asymptotic flatness of the radial velocity dispersion of spiral galaxies, the accelerated expanding universe and the Pioneer 10/11 anomaly in the entropic force framework of Verlinde.

 

Application of Bayesian model averaging to measurements of the primordial power spectrum

Authors: David Parkinson, Andrew R. Liddle

http://arxiv.org/abs/1009.1394v1

Cosmological parameter uncertainties are often stated assuming a particular model, neglecting the model uncertainty, even when Bayesian model selection is unable to identify a conclusive best model. Bayesian model averaging is a method for assessing parameter uncertainties in situations where there is also uncertainty in the underlying model. We apply model averaging to the estimation of the parameters associated with the primordial power spectra of curvature and tensor perturbations. We use CosmoNest and MultiNest to compute the model Evidences and posteriors, using cosmic microwave data from WMAP, ACBAR, BOOMERanG and CBI, plus large-scale structure data from the SDSS DR7. We find that the model-averaged 95% credible interval for the spectral index using all of the data is 0.940 < n_s < 1.000, where n_s is specified at a pivot scale 0.015 Mpc^{-1}. For the tensors model averaging can tighten the credible upper limit, depending on prior assumptions.

 

N-body Simulations for Extended Quintessence Models

Authors: Baojiu Li, David F. Mota, John D. Barrow

http://arxiv.org/abs/1009.1400v1

We introduce the N-body simulation technique to follow structure formation in linear and nonlinear regimes for the extended quintessence models (scalar-tensor theories in which the scalar field has a self-interaction potential and behaves as dark energy), and apply it to a class of models specified by an inverse power-law potential and a non-minimal coupling. Our full solution of the scalar field perturbation confirms that, when the potential is not too nonlinear, the effects of the scalar field could be accurately approximated as a modification of background expansion rate plus a rescaling of the effective gravitational constant relevant for structure growth. For the models we consider, these have opposite effects, leading to a weak net effect in the linear perturbation regime. However, on the nonlinear scales the modified expansion rate dominates and could produce interesting signatures in the matter power spectrum and mass function, which might be used to improve the constraints on the models from cosmological data. We show that the density profiles of the dark matter halos are well described by the Navarro-Frenk-White formula, although the scalar field could change the concentration. We also derive an analytic formula for the scalar field perturbation inside halos assuming NFW density profile and sphericity, which agrees well with numerical results if the parameter is appropriately tuned. The results suggest that for the models considered, the spatial variation of the scalar field (and thus the locally measured gravitational constant) is very weak, and so local experiments could see the background variation of gravitational constant.

 

Voids in Coupled Scalar Field Cosmology

Authors: Baojiu Li

http://arxiv.org/abs/1009.1406v1

We study the properties of voids in two different types of coupled scalar field theories. Due to the fifth force produced by the scalar field coupling, the matter particles feel stronger attraction amongst each other and cluster more quickly than they do in the standard LCDM model. Consequently voids in the coupled scalar field theories start to develop earlier and end up bigger, which is confirmed by our numerical simulations. We find that a significantly larger portion of the whole space is under-densed in the coupled scalar field theories and there are more voids whose sizes exceed given thresholds. This is more prominent in early times because at later times the under-dense regions have already been evacuated in coupled scalar field theories and there is time for the LCDM model to catch up. The coupled scalar field theories also predict a sharper transition between voids and high density regions. All in all, the qualitative behaviour is different not only from the LCDM result, but also amongst specific coupled scalar field models, making voids a potential candidate to test alternative ideas about the cosmic structure formation.

 

Frontiers of Dark Energy

Authors: Eric V. Linder

http://arxiv.org/abs/1009.1411v1

Cosmologists are just beginning to probe the properties of the cosmic vacuum and its role in reversing the attractive pull of gravity to cause an acceleration in the expansion of the cosmos. The cause of this acceleration is given the generic name of dark energy, whether it is due to a true vacuum, a false, temporary vacuum, or a new relation between the vacuum and the force of gravity. Despite the common name, the distinction between these origins is of utmost interest and physicists are actively engaged in finding ways to use cosmological observations to distinguish which is the true, new physics. Here we will discuss how to relate the theoretical ideas to the experimental constraints, how to understand the influences of dark energy on the expansion and structure in the universe, and what frontiers of new physics are being illuminated by current and near-term data.

 

Improving CMB non-Gaussianity estimators using tracers of local structure

Authors: James M. G. Mead, Antony Lewis, Lindsay J. King

http://arxiv.org/abs/1009.1549v1

Local non-Gaussianity causes correlations between large scale perturbation modes and the small scale power. The large-scale CMB signal has contributions from the integrated Sachs Wolfe (ISW) effect, which does not correlate with the small scale power. If this ISW contribution can be removed, the sensitivity to local non-Gaussianity is improved. Gravitational lensing and galaxy counts can be used to trace the ISW contribution; in particular we show that the CMB lensing potential is highly correlated with the ISW signal. We construct a nearly-optimal estimator for the local non-Gaussianity parameter $\fnl$ and investigate to what extent we can use this to decrease the variance on ${\fnl}$. We show that the variance can be decreased by up to $20\%$ at Planck sensitivity using galaxy counts. CMB lensing is a good bias-independent ISW tracer for future more sensitive observations, though the fractional decrease in variance is small if good polarization data is also available.

 

arXiv: 8 September 2010

Dark Matter and Dark Energy as Effects of Quantum Gravity

Authors: Max I. Fomitchev

http://arxiv.org/abs/1009.1369v1

I present a theory of quantum gravity based on the principle of gravitational energy fluctuations. Gravitational energy fluctuations -- gravitons -- are responsible for elastic scattering of subatomic particles. Such scattering corresponds to complimentary force -- graviton scattering force -- arising in gravitational interaction in addition to Newtonian gravity. The strength of the graviton scattering force is proportional to the graviton scattering probability. Unlike Newtonian gravity the graviton scattering force follows the 1/r law and dominates the former on cosmological scale in the limit of low orbital accelerations. Similarly to Modified Newtonian Dynamics the quantum gravity accounts for variations in observed M/L ratios of diverse stellar systems ranging from dwarf spheroid galaxies to X-ray galaxy clusters without requiring an invisible matter (which is still required by MOND in X-Ray cluster cores). Unlike MOND the presented theory neither violates cornerstone Newton Laws nor suffers from the ambiguity of acceleration frames while enjoying vast experimental evidence usually cited in favor of MOND. To ascertain the validity of the presented theory I have examined the predictions of quantum gravity for dwarf spheroid, ordinary and giant elliptic galaxies, and X-ray clusters. In all cases quantum gravity yields M/L ratios and scaling relations consistent with observations. Quantum gravity accounts for the tilt of the Fundamental Plane of elliptical galaxies erasing the differences in M/L vs. luminosity relations for faint and bright ellipticals, which cannot be easily explained by CDM model. Lastly, by analyzing the behavior of the gravitational energy fluctuations in the limit of high matter density expected in the early Universe I show that primordial inflation and dark energy (i.e. non-zero cosmological constant) arise as natural effects of quantum gravity in the expanding Universe.

 

 

arXiv: 7 September 2010

Large-scale bias of dark matter halos

Authors: Patrick Valageas

http://arxiv.org/abs/1009.1131v1

We build a simple analytical model for the bias of dark matter halos that applies to objects defined by an arbitrary density threshold, $200\leq\delta\leq 1600$, and that provides accurate predictions from low-mass to high-mass halos. We point out that it is possible to build simple and efficient models, with no free parameter for the halo bias, by using integral constraints that govern the behavior of low-mass and typical halos, whereas the properties of rare massive halos are derived through explicit asymptotic approaches. We also describe how to take into account the impact of halo motions on their bias, using their linear displacement field. We obtain a good agreement with numerical simulations for the halo mass functions and large-scale bias at redshifts $0\leq z \leq 2.5$, for halos defined by nonlinear density threshold $200\leq\delta\leq 1600$. We also evaluate the impact on the halo bias of two common approximations, i) neglecting halo motions, and ii) linearizing the halo two-point correlation

 

Cosmography: Supernovae Union2, Observational Hubble Data, Gamma Ray Bursts and Angular Diameter Distance

Authors: Lixin Xu, Yuting Wang

http://arxiv.org/abs/1009.0963v1

In this paper, a parameterization describing the kinematical state of the universe in cosmographic approach is considered, where the minimum input is the assumption of the cosmological principle, i.e. the Friedmann-Robertson-Walker metric. A distinguished feature is that the result does not depend on any gravity theory. As a result, a series of cosmographic parameters (deceleration parameter $q_0$, jerk parameter $j_0$ and snap parameter $s_0$) are constrained from the cosmic observations which include type Ia supernovae (SN) Union2, the high redshift Gamma ray bursts (GRBs), the observational Hubble data (OHD) and angular diameter distance (ADD). By using Markov Chain Monte Carlo (MCMC) method, we find the best fit values of cosmographic parameters in $1\sigma$ regions: $H_0=72.009^{+6.073}_{-5.834}$, $q_0=-0.641^{+0.415}_{-0.360}$, $j_0=-2.214^{+3.635}_{-3.924}$, $s_0=-13.875^{+6.668}_{-6.218}$ which are improved remarkably and consistent with the spatially flat $\Lambda$CDM model.

 

!!!Observational evidence favours a static universe

Authors: David F. Crawford

http://arxiv.org/abs/1009.0953v1

The common attribute of all Big Bang cosmologies is that they are based on the assumption that the universe is expanding. However examination of the evidence for this expansion clearly favours a static universe. The major topics considered are: Tolman surface brightness, angular size, type 1a supernovae, gamma ray bursts, galaxy distributions, quasar distributions, X-ray background radiation, cosmic microwave background radiation, radio source counts, quasar variability and the Butcher--Oemler effect. An analysis of the best raw data for these topics shows that they are consistent with expansion only if there is evolution that cancels the effects of expansion. An alternate cosmology, curvature cosmology, is in full agreement with the raw data. This tired-light cosmology predicts a well defined static and stable universe and is fully described. It not only predicts accurate values for the Hubble constant and the temperature of cosmic microwave background radiation but shows excellent agreement with most of the topics considered. Curvature cosmology also predicts the deficiency in solar neutrino production rate and can explain the anomalous acceleration of {\it Pioneer} 10.

 

The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectra

Authors: J. Dunkley, R. Hlozek, J. Sievers, V. Acquaviva, P. A. R. Ade, P. Aguirre, M. Amiri, J. W. Appel, L. F. Barrientos, E. S. Battistelli, J. R. Bond, B. Brown, B. Burger, J. Chervenak, S. Das, M. J. Devlin, S. R. Dicker, W. Bertrand Doriese, R. Dunner, T. Essinger-Hileman, R. P. Fisher, J. W. Fowler, A. Hajian, M. Halpern, M. Hasselfield, C. Hernandez-Monteagudo, G. C. Hilton, M. Hilton, A. D. Hincks, K. M. Huffenberger, D. H. Hughes, J. P. Hughes, L. Infante, K. D. Irwin, J. B. Juin, M. Kaul, J. Klein, A. Kosowsky, J. M Lau, M. Limon, Y-T. Lin, R. H. Lupton, T. A. Marriage, D. Marsden, P. Mauskopf, F. Menanteau, K. Moodley, H. Moseley, C. B Netterfield, M. D. Niemack, M. R. Nolta, L. A. Page, L. Parker, B. Partridge, B. Reid, N. Sehgal, B. Sherwin, D. N. Spergel, S. T. Staggs, D. S. Swetz,

E. R. Switzer, R. Thornton, H. Trac, C. Tucker, R. Warne, E. Wollack, Y. Zhao

et al. (7 additional authors not shown)

http://arxiv.org/abs/1009.0866v1

We present cosmological parameters derived from the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz over 296 deg^2 with the Atacama Cosmology Telescope (ACT) during its 2008 season. ACT measures fluctuations at scales 500<l<10000. We fit a model for the lensed CMB, Sunyaev-Zel'dovich (SZ), and foreground contribution to the 148 GHz and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from radio and infrared point sources, and clustered power from infrared point sources. The power from thermal and kinetic SZ at 148 GHz is estimated to be B_3000 = 6.8+-2.9 uK^2, where B_l=l(l+1)C_l/2pi. We estimate primary cosmological parameters from the 148 GHz spectrum, marginalizing over SZ and source power. The LCDM cosmological model is a good fit to the data, and LCDM parameters estimated from ACT+WMAP are consistent with the 7-year WMAP limits, with scale invariant n_s = 1 excluded at 99.7% CL (3sigma). A model with no CMB lensing is disfavored at 2.8sigma. By measuring the third to seventh acoustic peaks, and probing the Silk damping regime, the ACT data improve limits on cosmological parameters that affect the small-scale CMB power. The ACT data combined with WMAP give a 6sigma detection of primordial helium, with Y_P = 0.313+-0.044, and a 4sigma detection of relativistic species, assumed to be neutrinos, with Neff = 5.3+-1.3 (4.6+-0.8 with BAO+H0 data). From the CMB alone the running of the spectral index is constrained to be dn/dlnk = -0.034 +- 0.018, the limit on the tensor-to-scalar ratio is r<0.25 (95% CL), and the possible contribution of Nambu cosmic strings to the power spectrum is constrained to string tension Gmu<1.6 \times 10^-7 (95% CL).

 

The Small Scale Structure of Spacetime

Authors: Steven Carlip

http://arxiv.org/abs/1009.1136v1

Several lines of evidence hint that quantum gravity at very small distances may be effectively two-dimensional. I summarize the evidence for such ``spontaneous dimensional reduction,'' and suggest an additional argument coming from the strong-coupling limit of the Wheeler-DeWitt equation. If this description proves to be correct, it suggests a fascinating relationship between small-scale quantum spacetime and the behavior of cosmologies near an asymptotically silent singularity.

 

arXiv: 6 September 2010

Combining perturbation theories with halo models

Authors: Patrick Valageas, Takahiro Nishimichi
http://arxiv.org/abs/1009.0597v1

We investigate the building of unified models that can predict the matter density power spectrum, and the two-point correlation function, from very large to small scales, being consistent with perturbation theory at low $k$ and with halo models at high $k$. We use a Lagrangian framework to re-interpret the halo model and to decompose the power spectrum into "2-halo" and "1-halo" contributions, related to "perturbative" and "non-perturbative" terms. We describe a simple implementation of this model and we present a detailed comparison with numerical simulations, from $k \sim 0.02$ up to $100 h$Mpc$^{-1}$, and from $x \sim 0.02$ up to $150 h^{-1}$Mpc. We show that the 1-halo contribution contains a counterterm that ensures a $k^2$ tail at low $k$ and is important not to spoil the predictions at the scales probed by baryon acoustic oscillations, $k \sim 0.02$ to $0.3 h$Mpc$^{-1}$. On the other hand, we show that standard perturbation theory is inadequate for the 2-halo contribution, because higher-order terms grow too fast at high $k$, so that resummation schemes must be used. We describe a simple implementation, based on a 1-loop "direct steepest-descent" resummation for the 2-halo contribution that allows fast numerical computations, and we check that we obtain a good match to simulations at low and high $k$.Our simple implementation already fares better than standard 1-loop perturbation theory at large scales and than simple fits to the power spectrum at high $k$, with a typical accuracy of 1% at large scales and 10% at small scales. We obtain similar results for the two-point correlation function. However, there remains room for improvement at the transition scale between the 2-halo and 1-halo contributions, which may be the most difficult regime to describe.

 

 

arXiv: 3 September 2010

Orbit of the Large Magellanic Cloud in a Dynamical Model for the Local Group

Authors: P. J. E. Peebles

http://arxiv.org/abs/1009.0496v1

A mass model that includes galaxies in and near the Local Group and an external mass in the direction of the Maffei system, with the condition from cosmology that protogalaxies have small peculiar velocities at high redshifts, allows a plausible picture for the past motion of the Large Magellanic Cloud relative to the Milky Way. The model also fits the proper motions of M33 and IC10.

arXiv: 2 September 2010

Determination of Dark Energy by the Einstein Telescope: Comparing with CMB, BAO and SNIa Observations

Authors: W. Zhao, C. Van Den Broeck, D. Baskaran, T.G.F. Li

http://arxiv.org/abs/1009.0206v2

A design study is currently in progress for a third generation gravitational-wave (GW) detector called Einstein Telescope (ET). An important kind of source for ET will be the inspiral and merger of binary neutron stars (BNS) up to $z \sim 2$. If BNS mergers are the progenitors of short-hard $\gamma$-ray bursts, then some fraction of them will be seen both electromagnetically and through GW, so that the luminosity distance and the redshift of the source can be determined separately. An important property of these `standard sirens' is that they are \emph{self-calibrating}: the luminosity distance can be inferred directly from the GW signal, with no need for a cosmic distance ladder. Thus, standard sirens will provide a powerful independent check of the $\Lambda$CDM model. In previous work, estimates were made of how well ET would be able to measure a subset of the cosmological parameters (such as the dark energy parameter $w_0$) it will have access to, assuming that the others had been determined to great accuracy by alternative means. Here we perform a more careful analysis by explicitly using the potential Planck CMB data as prior information for these other parameters. We find that ET will be able to constrain $w_0$ and $w_a$ with accuracies $\Delta w_0 = 0.096$ and $\Delta w_a = 0.296$, respectively. These results are compared with projected accuracies for the JDEM Baryon Acoustic Oscillations (BAO) project and the SNAP Type Ia supernovae (SNIa) observations.

 

Spherical collapse of dark energy with an arbitrary sound speed

Authors: Ole Eggers Bjaelde, Yvonne Y. Y. Wong

http://arxiv.org/abs/1009.0010v1

We consider a generic type of dark energy fluid, characterised by a constant equation of state parameter w and sound speed c_s, and investigate the impact of dark energy clustering on cosmic structure formation using the spherical collapse model. Along the way, we also discuss in detail the evolution of dark energy perturbations in the linear regime. We find that the introduction of a finite sound speed into the picture necessarily induces a scale-dependence in the dark energy clustering, which in turn affects the dynamics of the spherical collapse in a scale-dependent way. As with other, more conventional fluids, we can define a Jeans scale for the dark energy clustering, and hence a Jeans mass M_J for the dark matter which feels the effect of dark energy clustering via gravitational interactions. For bound objects (halos) with masses M >> M_J, the effect of dark energy clustering is maximal. For those with M << M_J, the dark energy component is effectively homogeneous, and its role in the formation of these structures is reduced to its effects on the Hubble expansion rate. For the virial density and linearly extrapolated threshold density, we find an interesting dependence of their values on the halo mass M, given some w and c_s. The dependence is the strongest for masses lying in the vicinity of M ~ M_J. Observing this M-dependence will be a tell-tale sign that dark energy is dynamic, and a great leap towards pinning down its clustering properties.

 

arXiv: 1 September 2010

Hydrodynamical simulations of galaxy clusters in dark energy cosmologies: I. general properties

Authors: Cristiano De Boni, Klaus Dolag, Stefano Ettori, Lauro Moscardini, Valeria Pettorino, Carlo Baccigalupi

http://arxiv.org/abs/1008.5376v1

We investigate the influence of dark energy on structure formation, within five different cosmological models, namely a concordance $\Lambda$CDM model, two models with dynamical dark energy, viewed as a quintessence scalar field (using a RP and a SUGRA potential form) and two extended quintessence models (EQp and EQn) where the quintessence scalar field interacts non-minimally with gravity (scalar-tensor theories). We adopted for all models the normalization of the matter power spectrum $\sigma_{8}$ to match the CMB data. In the models with dynamical dark energy and quintessence, we describe the equation of state with $w_0\approx-0.9$, still within the range still allowed by observations. For each model, we have performed hydrodynamical simulations in a cosmological box of (300 Mpc/{\em h})$^{3}$ including baryons and allowing for cooling and star formation. The contemporary presence of evolving dark energy and baryon physics allows us to investigate the interplay between the different background cosmology and the evolution of the luminous matter. Since cluster baryon fraction can be used to constrain other cosmological parameters such as $\Omega_{m}$, we analyse also how dark energy influences the baryon content of galaxy clusters. We find that in models with dynamical dark energy, the interplay between the evolving cosmological background, the star formation rate and the baryon physics leads to very different formation histories of galaxy clusters.We evaluate the cosmological volumes needed to distinguish the dark energymodels here investigated using the cluster number counts (in terms of the mass function and the X-ray luminosity and temperature functions). The X-ray temperature function appears to be more sensitive to trace the underlying mass function, with differences up to a factor of two depending on the dark energy model considered.

 

CMB constraints on the energy scale of inflation

Authors: Zong-Kuan Guo, Dominik J. Schwarz, Yuan-Zhong Zhang

http://arxiv.org/abs/1008.5258v1

Determining the energy scale of inflation is crucial to understand the nature of inflation in the early Universe. We place observational constraints on the energy scale of the observable part of the inflaton potential by combining the 7-year Wilkinson Microwave Anisotropy Probe data with distance measurements from the baryon acoustic oscillations in the distribution of galaxies and the Hubble constant measurement. Our analysis provides an upper limit on this energy scale, 2.3 \times 10^{16} GeV at 95% confidence level. Moreover, we forecast the sensitivity and constraints achievable by the Planck experiment by performing Monte Carlo studies on simulated data. Planck could significantly improve the constraints on the energy scale of inflation and on the shape of the inflaton potential.

arXiv: 31 August 2010

Assembly History and Structure of Galactic Cold Dark Matter Halos

Authors: Jie Wang, J. F. Navarro, C. S. Frenk, S. D. M. White, V. Springel, A. Jenkins, A. Helmi, A. Ludlow, M. Vogelsberger

http://arxiv.org/abs/1008.5114v2

We use the Aquarius simulation series to study the imprint of assembly history on the structure of Galaxy-mass cold dark matter halos. Our results confirm earlier work regarding the influence of mergers on the mass density profile and the inside-out growth of halos. The inner regions that contain the visible galaxies are stable since early times and are significantly affected only by major mergers. Particles accreted diffusely or in minor mergers are found predominantly in the outskirts of halos. Our analysis reveals trends that run counter to current perceptions of hierarchical halo assembly. For example, major mergers (i.e. those with progenitor mass ratios greater than 1:10) contribute little to the total mass growth of a halo, on average less than 20 per cent for our six Aquarius halos. The bulk is contributed roughly equally by minor mergers and by "diffuse" material which is not resolved into individual objects. This is consistent with modeling based on excursion-set theory which suggests that about half of this diffuse material should not be part of a halo of any scale. Interestingly, the simulations themselves suggest that a significantly fraction is not truly diffuse, since it was ejected from earlier halos by mergers prior to their joining the main system. The Aquarius simulations resolve halos to much lower mass scales than are expected to retain gas or form stars. These results thus confirm that most of the baryons from which visible galaxies form are accreted diffusely, rather than through mergers, and they suggest that only relatively rare major mergers will affect galaxy structure at later times.

 

Galactic foregrounds and CMB polarization

Authors: E. Carretti

http://arxiv.org/abs/1008.4983v1

The CMB polarization promises to unveil the dawn of time measuring the gravitational wave background emitted by the Inflation. The CMB signal is faint, however, and easily contaminated by the Galactic foreground emission, accurate measurements of which are thus crucial to make CMB observations successful. We review the CMB polarization properties and the current knowledge on the Galactic synchrotron emission, which dominates the foregrounds budget at low frequency. We then focus on the S-Band Polarization All Sky Survey (S-PASS), a recently completed survey of the entire southern sky designed to investigate the Galactic CMB foreground.

 

Evolution of primordial planets in relation to the cosmological origin of life

Authors: N. Chandra Wickramasinghea (Cardiff Univ. UK), Jamie H. Wallis (Cardiff Univ. UK), Carl H. Gibson (Univ. Cal. San Diego US), Rudolph E. Schild (Harvard Univ. US)

http://arxiv.org/abs/1008.4955v1

We explore the conditions prevailing in primordial planets in the framework of the HGD cosmologies as discussed by Gibson and Schild. The initial stages of condensation of planet-mass H-4He gas clouds in trillion-planet clumps is set at 300,000 yr (0.3My) following the onset of plasma instabilities when ambient temperatures were >1000K. Eventual collapse of the planet-cloud into a solid structure takes place against the background of an expanding universe with declining ambient temperatures. Stars form from planet mergers within the clumps and die by supernovae on overeating of planets. For planets produced by stars, isothermal free fall collapse occurs initially via quasi equilibrium polytropes until opacity sets in due to molecule and dust formation. The contracting cooling cloud is a venue for molecule formation and the sequential condensation of solid particles, starting from mineral grains at high temperatures to ice particles at lower temperatures, water-ice becomes thermodynamically stable between 7 and 15 My after the initial onset of collapse, and contraction to form a solid icy core begins shortly thereafter. Primordial-clump-planets are separated by ~ 1000 AU, reflecting the high density of the universe at 30,000 yr. Exchanges of materials, organic molecules and evolving templates readily occur, providing optimal conditions for an initial origin of life in hot primordial gas planet water cores when adequately fertilized by stardust. The condensation of solid molecular hydrogen as an extended outer crust takes place much later in the collapse history of the protoplanet. When the object has shrunk to several times the radius of Jupiter, the hydrogen partial pressure exceeds the saturation vapour pressure of solid hydrogen at the ambient temperature and condensation occurs.

 

The Joint Dark Energy Mission (JDEM) Omega

Authors: Neil Gehrels

http://arxiv.org/abs/1008.4936v1

[JDEM-Omega is one of the three concepts that contributed to the Wide-Field Infrared Survey Telescope (WFIRST) mission advocated by the Astro2010 Decadal Survey. It is the concept on which the recommended observatory configuration is based.] The Joint Dark Energy Mission (JDEM) is a space-based observatory designed to perform precision measurements of the nature of dark energy in the Universe. It will make an order of magnitude progress in measuring the equation of state parameters of the Universe of most importance for understanding dark energy. JDEM-Omega is a wide-field space telescope operating in the near infrared. Dark energy measurements will be made via large surveys of galaxies and supernova monitoring. These will be an order of magnitude larger surveys than currently available and will provide enormous catalogs of astrophysical objects for many communities ranging from solar system to galaxy to galaxies/clusters to cosmology. JDEM-Omega is a mission concept collaboratively developed by NASA and the Department of Energy, with substantial input from the JDEM Science Coordination Group and community at large.

 

Model independent dark energy constraints from the correlation function of the Sloan Digital Sky Survey DR7 luminous red galaxies

Authors: Chia-Hsun Chuang, Yun Wang, Maddumage Don P. Hemantha

http://arxiv.org/abs/1008.4822v1

We measure the constraints of the cosmological parameters from the overall shape of the spherically averaged two-point correlation function of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy (LRG) sample without assuming a dark energy model or a flat universe. We obtain the covariance matrix of an effective distance to $z=0.35$, $D_V(0.35)$, and three cosmological parameters, $\Omega_m h^2$, $\Omega_b h^2$, and $n_s$. We find $\Omega_mh^2=0.110\pm0.010$ with flat priors on $\Omega_bh^2$ and $n_s$ (7$\sigma_{WMAP7}$). The correlation function also constrains the ratio of the comoving sound horizon at the baryon-drag epoch to the effective distance to $z=0.35$: $r_s/D_V(0.35)=0.1137\pm0.0028$. Our measurement of $\Omega_m h^2$ is smaller than other determinations in the literature by more than $2\sigma$. We find that it can be explained by varying the scale range analyzed and we argue that the scale range we use is conservative. We also measure the Hubble parameter and angular diameter distance from the spherically averaged correlation function and obtain $H(0.35)=79.5^{+8.7}_{-8.8}$ km s$^{-1}$Mpc$^{-1}$ and $D_A(0.35)=1068^{+67}_{-68}$ Mpc. Combining our results with the cosmic microwave background (CMB) and supernovae (SNe) data, we find that $\Omega_k=-0.003\pm0.006$ and $w=-0.977^{+0.042}_{-0.041}$ (assuming a constant dark energy equation of state $w$).

 

Cosmological Constraints from Strong Gravitational Lensing in Galaxy Clusters

Authors: Eric Jullo, Priyamvada Natarajan, Jean-Paul Kneib, Anson d'Aloisio, Marceau Limousin, Johan Richard, Carlo Schimd

http://arxiv.org/abs/1008.4802v1

Current efforts in observational cosmology are focused on characterizing the mass-energy content of the Universe. We present results from a geometric test based on strong lensing in galaxy clusters. Based on Hubble Space Telescope images and extensive ground-based spectroscopic follow-up of the massive galaxy cluster Abell 1689, we used a parametric model to simultaneously constrain the cluster mass distribution and dark energy equation of state. Combining our cosmological constraints with those from X-ray clusters and the Wilkinson Microwave Anisotropy Probe 5-year data gives {\Omega}m = 0.25 +/- 0.05 and wx = -0.97 +/- 0.07 which are consistent with results from other methods. Inclusion of our method with all other techniques available brings down the current 2{\sigma} contours on the dark energy equation of state parameter wx by about 30%.

 

SZ effects from annihilating dark matter in the Milky Way: smooth halo, subhalos and intermediate-mass-black-holes

Authors: Julien Lavalle

http://arxiv.org/abs/1008.5124v1

We study the Sunyaev-Zel'dovich (SZ) effect potentially generated by relativistic electrons injected from dark matter (DM) annihilation or decay in the Galaxy, and check whether it could be observed by Planck or ALMA, or even imprint the current CMB data as e.g. the specific fluctuation excess claimed from an recent re-analysis of the WMAP-5 data. We focus on high-latitude regions to avoid contamination of the Galactic astrophysical electron foreground, and consider the annihilation or decay coming from the smooth DM halo as well as from subhalos, further extending our analysis to a generic modeling of spikes arising around intermediate-mass-black-holes (IMBHs). We show that all these dark Galactic components are unlikely to produce any observable SZ effect. For a self-annihilating DM particle of 10 GeV with canonical properties, the largest optical depth we find is $\tau_e \lesssim 10^{-7}$ for massive isolated subhalos hosting IMBHs. We conclude that dark matter annihilation or decay on the Galactic scale cannot lead to significant SZ distortions of the CMB spectrum.

 

 

arXiv: 30 August 2010

Primordial Nucleosynthesis: The Predicted and Observed Abundances and Their Consequences

Authors: Gary Steigman

http://arxiv.org/abs/1008.4765v1

For a brief time in its early evolution the Universe was a cosmic nuclear reactor. The expansion and cooling of the Universe limited this epoch to the first few minutes, allowing time for the synthesis in astrophysically interesting abundances of only the lightest nuclides (D, 3He, 4He, 7Li). For big bang nucleosynthesis (BBN) in the standard models of cosmology and particle physics (SBBN), the SBBN-predicted abundances depend on only one adjustable parameter, the baryon density parameter (the ratio by number of baryons (nucleons) to photons). The predicted and observed abundances of the relic light elements are reviewed, testing the internal consistency of primordial nucleosynthesis. The consistency of BBN is also explored by comparing the values of the cosmological parameters inferred from primordial nucleosynthesis for the standard model and for models with non-standard early Universe expansion rates with those determined from studies of the cosmic background radiation, which provides a snapshot of the Universe some 400 thousand years after BBN ended.

 

The Misalignments between Matter and Galaxy Distributions in Triaxial Clusters: A Signature of a Possible Fifth Force?

Authors: Jounghun Lee (Seoul National University)

http://arxiv.org/abs/1008.4620v1

The standard structure formation model based on a LCDM cosmology predicts that the galaxy clusters have triaxial shapes and that the cluster galaxies have a strong tendency to be located preferentially along the major axes of host cluster's dark matter distributions due to the gravitational tidal effect. The predicted correlations between dark matter and galaxy distributions in triaxial clusters are insensitive to the initial cosmological parameters and to the galaxy bias, and thus can provide a unique test-bed for the nonlinear structure formation of the LCDM cosmology. Recently, Oguri et al. determined robustly the dark matter distributions in the galaxy clusters using the two dimensional weak lensing shear fitting and showed that the orientations of the cluster galaxy distributions are only very weakly correlated with those of the underlying dark matter distributions determined robustly, which is in contrast to with the LCDM-based prediction. We reanalyze and compare quantitatively the observational result with the LCDM-based prediction from the Millennium Run simulation with the help of the bootstrap resampling and generalized chi^{2}-statistics. The hypothesis that the observational result is consistent with the LCDM-based prediction is ruled out at the 99% confidence level. A local fifth force induced by a non-minimal coupling between dark energy and dark matter might be responsible for the observed misalignments between dark matter and galaxy distributions in triaxial clusters.

 

A Halo Model with Environment Dependence: Theoretical Considerations

Authors: Héctor Gil-Marín, Raul Jimenez, Licia Verde

http://arxiv.org/abs/1008.4583v1

We present a modification of the standard halo model with the goal of providing an improved description of galaxy clustering. Recent surveys, like the Sloan Digital Sky Survey (SDSS) and the Anglo-Australian Two-degree survey (2dF), have shown that there seems to be a correlation between the clustering of galaxies and their properties such as metallicity and star formation rate, which are believed to be environment-dependent. This environmental dependence is not included in the standard halo model where the host halo mass is the only variable specifying galaxy properties. In our approach, the halo properties i.e., the concentration, and the Halo Occupation Distribution --HOD-- prescription, will not only depend on the halo mass (like in the standard halo model) but also on the halo environment. We examine how different environmental dependence of halo concentration and HOD prescription affect the correlation function. We see that at the level of dark matter clustering, the concentration of haloes does not affect considerably to the dark matter correlation function. However the galaxy correlation function is extremely sensitive to the HOD details, even when only the HOD of a small fraction of haloes is modified. In particular, the galaxy correlation function is most sensitive to the minimum mass for a halo to host a galaxy and the number of satellite galaxies for a given halo mass and environment.