Evolution of the fσ8 tension with the Planck15/ΛCDM determination and implications for modified gravity theories

Abstract

We construct an updated extended compilation of distinct (but possibly correlated) f σ8(z) redshift space distortion (RSD) data published between 2006 and 2018. It consists of 63 data points and is significantly larger than previously used similar data sets. After fiducial model correction we obtain the best fit Ω0m − σ8 ΛCDM parameters and show that they are at a 5σ tension with the corresponding Planck15/ΛCDM values. Introducing a nontrivial covariance matrix correlating randomly 20% of the RSD data points has no significant effect on the above tension level. We show that the tension disappears (becomes less than 1σ) when a subsample of the 20 most recently published data is used. A partial cause for this reduced tension is the fact that more recent data tend to probe higher redshifts (with higher errorbars) where there is degeneracy among different models due to matter domination. Allowing for a nontrivial evolution of the effective Newton's constant(ga is a parameter) and fixing a Planck15/ΛCDM background we find ga = −0.91 ± 0.17 from the full f σ8 data set while the 20 earliest and 20 latest data points imply ga = −1.28 +0.28 −0.26 and ga = −0.43 +0.46 −0.41 respectively. Thus, the more recent f σ8 data appear to favor GR in contrast to earlier data. Finally, we show that the parametrization f σ8(z) = λσ8Ω(z) γ /(1 + z) β provides an excellent fit to the solution of the growth equation for both GR (ga = 0) and modified gravity (ga = 0).

Tension of the EG statistic and redshift space distortion data with the Planck - ΛCDM model and implications for weakening gravity

“…Dynamical probes include cluster counts (CC) [29][30][31][32], weak lensing (WL) [25,[33][34][35][36][37][38][39] and redshift-space distortions (RSD) [1,2,[40][41][42]. These probes are consistent with each other pointing either to a lower value of the matter density parameter Ω 0m in the context of GR or to weaker gravitational growth power than the growth indicated by GR in the context of a Planck18ΛCDM background geometry at about 2 − 3σ level [1,2,41]. Such weak growth may be quantified by the parameter σ 8 which is the density rms matter fluctuations within spheres of radius 8h −1 M pc and is determined by the amplitude of the primordial fluctuations power spectrum and by the growth rate of cosmological fluctuation.…”

“…The former includes the effects of interacting dark energy models [43][44][45][46], dynamical dark energy models [47,48], running vacuum models [49,50] and the effects of massive neutrinos [51]. The latter includes the effects of MG theories with a reduced (compared to GR) evolving effective Newton's constant G ef f at low redshifts [1,2]. The effects of MG [52][53][54][55][56][57][58][59][60][61] models are indistinguishable from GR at the geometric cosmological background level [26,62,63].…”

Implications of the possible 21-cm line excess at cosmic dawn on dynamics of interacting dark energy

“…The cosmological 21-cm line is caused by the hyperfine splitting of neutral hydrogen atoms, whose wavelength corresponds to the transition from the triplet state to the singlet state of the electron. We use the brightness temperature T 21 to describe the strength of the global 1 Cosmological models involving non-gravitational interactions between dark energy and dark matter were extensively studied in literatures [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68]. For instance see [50] for the early study, see [51] for the alleviation of coincidence problem of the current cosmic acceleration, and see [52] for a review.…”

Gravity in the infrared and effective nonlocal models

“…Actually, many more measurement exists: ref [143]. provides a compilation of 63 measurement of f σ8 from 2006 to 2018.…”

“…provides a compilation of 63 measurement of f σ8 from 2006 to 2018. However, as stressed in[143], many of these datapoints are correlated, due to overlap in the galaxy samples used, and no covariance matrix is available for the full dataset, nor for most of its subsets. Furthermore, one must also take care of the fact that different datapoints have been obtained with different fiducial cosmologies, and that survey systematic may vary with time of publication and lead to inhomogeneities in the data.…”