Evolution of the $fσ_8$ tension with the Planck15/$Λ$CDM determination and implications for modified gravity theories

Kazantzidis, Lavrentios; Perivolaropoulos, Leandros

doi:10.48550/arxiv.1803.01337

Cited by 35 publications

(50 citation statements)

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“…Values measured below these bounds, and such models were found earlier, would hint at either modified gravity (see e.g. [26], [27]) or interacting DE models (see e.g. [28,29]).…”

Section: Discussionsupporting

confidence: 56%

Consistency of the expansion of the Universe with density perturbations

Gannouji

Polarski

2018

Phys. Rev. D

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Assuming a simple form for the growth index γ(z) depending on two parameters γ0 ≡ γ(z = 0) and γ1 ≡ γ ′ (z = 0), we show that these parameters can be constrained using background expansion data. We explore systematically the preferred region in this parameter space. Inside General Relativity we obtain that models with a quasi-static growth index and γ1 ≈ −0.02 are favoured. We find further the lower bounds γ0 0.53 and γ1 −0.15 for models inside GR. Models outside GR having the same background expansion as ΛCDM and arbitrary γ(z) with γ0 = γ ΛCDM 0 , satisfy G eff,0 > G for γ1 > γ ΛCDM 1 , and G eff,0 < G for γ1 < γ ΛCDM 1 . The first models will cross downwards the value G eff = G on very low redshifts z < 0.3, while the second models will cross upwards G eff = G in the same redshift range. This makes the realization of such modified gravity models even more problematic.

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“…Values measured below these bounds, and such models were found earlier, would hint at either modified gravity (see e.g. [26], [27]) or interacting DE models (see e.g. [28,29]).…”

Section: Discussionsupporting

confidence: 56%

Consistency of the expansion of the Universe with density perturbations

Gannouji

Polarski

2018

Phys. Rev. D

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“…In another vein, we have some trouble in the structure formation data. The concordance model predicts a value of σ 8 (the current matter density rms fluctuations within spheres of radius 8h −1 Mpc, with h 0.7 the reduced Hubble constant) in excess by 2−3σ over the direct data values at low redshifts [26,27,[33][34][35][36]; more specifically, the tension is in between measurements of the amplitude of the power spectrum of density perturbations inferred using CMB data against those directly measured by Large-Scale Structure (LSS) formation on smaller scales, from redshift space distortions (RSD) (see e.g. [37]) and Weak-Lensing (WL) data [38][39][40][41].…”

Section: Introductionmentioning

confidence: 90%

Brans–Dicke cosmology with a Λ-term: a possible solution to ΛCDM tensions*

Peracaula

Gómez-Valent

Pérez

et al. 2020

Class. Quantum Grav.

145

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We present a full-fledged analysis of Brans–Dicke cosmology with a cosmological constant and cold dark matter (BD-ΛCDM for short). We extend the scenarios where the current cosmological value of the BD-field is restricted by the local astrophysical domain to scenarios where that value is fixed only by the cosmological observations, which should be more natural in view of the possible existence of local screening mechanism. Our analysis includes both the background and perturbations equations in different gauges. We find that the BD-ΛCDM is favored by the overall cosmological data as compared to the concordance GR-ΛCDM model, namely data on distant supernovae, cosmic chronometers, local measurements of the Hubble parameter, baryonic acoustic oscillations, large-scale structure formation and the cosmic microwave background under full Planck 2018 CMB likelihood. We also test the impact of strong and weak-lensing data on our results, which can be significant. We find that the BD-ΛCDM can mimic effective quintessence with a significance of about 3.0–3.5σ c.l. (depending on the lensing datasets). The fact that the BD-ΛCDM behaves effectively as a running vacuum model (RVM) when viewed from the GR perspective helps to alleviate some of the existing tensions with the data, such as the σ 8 excess predicted by GR-ΛCDM. On the other hand, the BD-ΛCDM model has a crucial bearing on the acute H 0-tension with the local measurements, which is rendered virtually harmless owing to the small increase of the effective value of the gravitational constant with the expansion. The simultaneous alleviation of the two tensions is a most remarkable feature of BD-gravity with a cosmological constant in the light of the current observations, and hence goes in support of BD-ΛCDM against GR-ΛCDM.

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“…However, recent analyses [31][32][33][34][35] indicate some tension between the Planck15/ΛCDM model and some dynamical observations measuring the growth rate of cosmological perturbations. Such observations include Weak Lensing data [36][37][38][39][40] and Redshift Space Distrortions (RSD) [1,2,31,[41][42][43]. The robust observable reported by RSD surveys is the product…”

Section: Introductionmentioning

confidence: 99%

“…Since 2006 there has been a significant increase of surveys that measure RSDs leading to a collection of 63 f σ 8 data points [2]. Despite possible correlations among the data points of this dataset its various subsamples considered in the literature [1,41,43,44] indicate various levels of tension between Planck15/ΛCDM parameter values and the parameter values favored by the considered f σ 8 subsample.…”

Section: Introductionmentioning

confidence: 99%

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Consistency of modified gravity with a decreasing Geff(z) in a ΛCDM background

et al. 2018

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Recent analyses [1,2] have indicated that an effective Newton's constant G eff (z) decreasing with redshift may relieve the observed tension between the Planck15 best fit ΛCDM cosmological background (i.e. Planck15/ΛCDM) and the corresponding ΛCDM background favored by growth f σ8 and weak lensing data. We investigate the consistency of such a decreasing G eff (z) with some viable scalar-tensor models and f (R) theories. We stress that f (R) theories generically can not lead to a decreasing G eff (z) for any cosmological background. For scalar-tensor models we deduce that in the context of a ΛCDM cosmological background, a decreasing G eff (z) is not consistent with a large Brans-Dicke parameter ωBD,0 today. This inconsistency remains and amplifies in the presence of a phantom dark energy equation of state parameter (w < −1). However it can be avoided for w > −1. We also find that any modified gravity model with the required decreasing G eff (z) and G eff,0 = G, would have a characteristic signature in its growth index γ with 0.61 γ0 0.69 and large slopes γ ′ 0 , 0.16 γ ′ 0 0.4, which is a characteristic signature of a decreasing (with z) G eff (z) < G on small redshifts. This is a substantial departure today from the quasi-static behaviour in ΛCDM with (γ0, γ ′ 0 ) ≈ (0.55, −0.02).

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Evolution of the $fσ_8$ tension with the Planck15/$Λ$CDM determination and implications for modified gravity theories

Cited by 35 publications

References 0 publications

Consistency of the expansion of the Universe with density perturbations

Consistency of the expansion of the Universe with density perturbations

Brans–Dicke cosmology with a Λ-term: a possible solution to ΛCDM tensions*

Consistency of modified gravity with a decreasing Geff(z) in a ΛCDM background

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