Large scale structure off(R)gravity

Abstract

We study the evolution of linear cosmological perturbations in f (R) models of accelerated expansion in the physical frame where the gravitational dynamics are fourth order and the matter is minimally coupled. These models predict a rich and testable set of linear phenomena. For each expansion history, fixed empirically by cosmological distance measures, there exists two branches of f (R) solutions that are parameterized by B ∝ d 2 f /dR 2 . For B < 0, which include most of the models previously considered, there is a short-timescale instability at high curvature that spoils agreement with high redshift cosmological observables. For the stable B > 0 branch, f (R) models can reduce the large-angle CMB anisotropy, alter the shape of the linear matter power spectrum, and qualitatively change the correlations between the CMB and galaxy surveys. All of these phenomena are accessible with current and future data and provide stringent tests of general relativity on cosmological scales.PACS numbers:

On the recovery of ISW fluctuations using large-scale structure tracers and CMB temperature and polarization anisotropies

“…For this reason the ISW effect provides a complementary tool to probe dark energy or models of modified gravity (e.g. Song, Hu, & Sawicki 2007;Pogosian & Silvestri 2008). The ISW signal is too small to be directly identified in the CMB spectrum, but it can be measured by correlating the CMB anisotropies and the large-scale structure (LSS; Crittenden & Turok 1996): maps of the distributions of galaxies are correlated with the ISW signal because they are tracers of the gravitational potential causing the ISW effect.…”

New constraints on parametrised modified gravity from correlations of the CMB with large scale structure

“…In general, the rate of clustering of dark matter, as well as the evolution of the metric potentials, is changed and can be scale-dependent. Moreover, typically there might be an effective anisotropic stress introduced by the modifications and the two potentials, Φ and Ψ, are not necessarily equal, as it was the case for ΛCDM [14,16,17,[19][20][21][22]44]. Here we focus on the effect of the modified evolution of the potential, Φ + Ψ, on the CMB.…”

“…λ 1 = 1/m 0 fR . In [14,48] this family of f (R) models was labelled by the parameter B 0 which is related to λ 1 via…”

“…In the standard ΛCDM theory, this effect is expected to be generated at late times as a consequence of the potential decay when the background starts accelerating. In models of modified gravity, such as f (R) theories, the magnitude of this late effect can be altered, as well as potentials can evolve during matter domination, therefore generating an ISW effect at earlier redshifts [14,16].…”

“…This requirement is twofold: at the background level, the predicted expansion history has to be coherent with distance measurements such as those from Supernovae (SNe), the position of the CMB peaks, and baryon acoustic oscillations (BAO); on the other hand, the modified predictions for structure formation need to pass the test of comparison with the observed large scale structure (LSS) of the Universe. It has been shown for several cases -for instance for f (R) [14][15][16][17][18] and DGP [19][20][21][22][23][24] -that the structure formation test can dramatically reduce the parameter space left unconstrained from the background test, and it is therefore instrumental to the quest for a truly viable model.…”