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Cosmology

About: Cosmology is a research topic. Over the lifetime, 18004 publications have been published within this topic receiving 631028 citations. The topic is also known as: physical cosmology & cosmologies.


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TL;DR: In this paper, the authors proposed an explanation for why the observed galaxy correlation function is not consistent with the predictions of the LambdaCDM model, through the application of Birkhoff's theorem and the Weyl postulate in the case of a flat spacetime.
Abstract: The backbone of standard cosmology is the Friedmann-Robertson-Walker solution to Einstein's equations of general relativity (GR). In recent years, observations have largely confirmed many of the properties of this model, which is based on a partitioning of the universe's energy density into three primary constituents: matter, radiation, and a hypothesized dark energy which, in LambdaCDM, is assumed to be a cosmological constant Lambda. Yet with this progress, several unpalatable coincidences (perhaps even inconsistencies) have emerged along with the successful confirmation of expected features. One of these is the observed equality of our gravitational horizon R_h(t_0) with the distance ct_0 light has traveled since the big bang, in terms of the current age t_0 of the universe. This equality is very peculiar because it need not have occurred at all and, if it did, should only have happened once (right now) in the context of LambdaCDM. In this paper, we propose an explanation for why this equality may actually be required by GR, through the application of Birkhoff's theorem and the Weyl postulate, at least in the case of a flat spacetime. If this proposal is correct, R_h(t) should be equal to ct for all cosmic time t, not just its present value t_0. Therefore models such as LambdaCDM would be incomplete because they ascribe the cosmic expansion to variable conditions not consistent with this relativistic constraint. We show that this may be the reason why the observed galaxy correlation function is not consistent with the predictions of the standard model. We suggest that an R_h=ct universe is easily distinguishable from all other models at large redshift (i.e., in the early universe), where the latter all predict a rapid deceleration.

158 citations

Journal ArticleDOI
TL;DR: In this article, the evolution of scalar perturbations in f(T) teleparallel gravity and its effects on the cosmic microwave background (CMB) anisotropy were investigated.
Abstract: We investigate the evolution of scalar perturbations in f(T) teleparallel gravity and its effects on the cosmic microwave background (CMB) anisotropy. The f(T) gravity generalizes the teleparallel gravity which is formulated on the Weitzenbock spacetime, characterized by the vanishing curvature tensor (absolute parallelism) and the non-vanishing torsion tensor. For the first time, we derive the observational constraints on the modified teleparallel gravity using the CMB temperature power spectrum from Planck's estimation, in addition to data from baryonic acoustic oscillations (BAO) and local Hubble constant measurements. We find that a small deviation of the f(T) gravity model from the ΛCDM cosmology is slightly favored. Besides that, the f(T) gravity model does not show tension on the Hubble constant that prevails in the ΛCDM cosmology. It is clear that f(T) gravity is also consistent with the CMB observations, and undoubtedly it can serve as a viable candidate amongst other modified gravity theories.

158 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of the formation of nonlinear structures on the expansion rate, spatial curvature and light propagation in the universe is reviewed, focusing on the possibility that it could explain cosmological observations without the introduction of dark energy or modified gravity.
Abstract: We review the effect of the formation of nonlinear structures on the expansion rate, spatial curvature and light propagation in the universe, focusing on the possibility that it could explain cosmological observations without the introduction of dark energy or modified gravity. We concentrate on explaining the relevant physics and highlighting open questions.

158 citations

Journal ArticleDOI
TL;DR: In this article, a smoothed template metric is proposed to compute quantities along an approximate effective light cone of the averaged model of the universe, which is used to quantify the ability of averaged inhomogeneous cosmologies to correctly describe observations of the large scale properties of the Universe.
Abstract: In order to quantitatively test the ability of averaged inhomogeneous cosmologies to correctly describe observations of the large-scale properties of the Universe, we introduce a smoothed template metric corresponding to a constant spatial curvature model at any time, but with an evolving curvature parameter. This metric is used to compute quantities along an approximate effective light cone of the averaged model of the Universe. As opposed to the standard Friedmann model, we parametrize this template metric by exact scaling properties of an averaged inhomogeneous cosmology, and we also motivate this form of the metric by results on a geometrical smoothing of inhomogeneous cosmological hypersurfaces. The purpose of the paper is not to demonstrate that the backreaction effect is actually responsible for the dark energy phenomenon by explicitly calculating the effect from a local model of the geometry and the distribution of matter, but rather to propose a way to deal with observations in the backreaction context, and to understand what kind of generic properties have to hold in order for a backreaction model to explain the observed features of the Universe on large scales. We test our hypothesis for the template metric against supernova data and the position of themore » cosmic microwave background peaks, and infer the goodness of fit and parameter uncertainties. We find that averaged inhomogeneous models can reproduce the observations without requiring an additional dark energy component (though a volume acceleration is still needed), and that current data do not disfavor our main assumption on the effective light cone structure. We also show that the experimental uncertainties on the angular diameter distance and the Hubble parameter from baryon acoustic oscillations measurements--forseen in future surveys like the proposed EUCLID satellite project--are sufficiently small to distinguish between a Friedmann-Lemaitre-Robertson-Walker template geometry and the template geometry with consistently evolving curvature.« less

157 citations

Journal ArticleDOI
TL;DR: In this paper, a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances Dds/Ds from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes.
Abstract: Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to collect a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances Dds/Ds from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes. On one hand, strongly gravitationally lensed quasar-galaxy systems create such a new opportunity by combining stellar kinematics (central velocity dispersion measurements) with lensing geometry (Einstein radius determination from position of images). We apply such a method to a combined gravitational lens data set including 70 data points from Sloan Lens ACS (SLACS) and Lens Structure and Dynamics survey (LSD). On the other hand, a new sample of 10 lensing galaxy clusters with redshifts ranging from 0.1 to 0.6 carefully selected from strong gravitational lensing systems with both X-ray satellite observations and optical giant luminous arcs, is also used to constrain three dark energy models (ΛCDM, constant w and CPL) under a flat universe assumption. For the full sample (n = 80) and the restricted sample (n = 46) including 36 two-image lenses and 10 strong lensing arcs, we obtain relatively good fitting values of basic cosmological parameters, which generally agree with the results already known in the literature. This results encourages further development of this method and its use on larger samples obtained in the future.

157 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
2023768
20221,518
2021737
2020784
2019782