Implications of a high growth index on the variation of $G$

Abstract

A recent determination of the growth index indicates a value significantly higher than the $\Lambda$CDM prediction, suggesting that alternative scenarios to $\Lambda$CDM may be required. In this work, we investigate whether a time-varying Newton's constant, $G_N$, can account for such a high growth index, $\gamma =0.063\pm 0.025$. Adopting a phenomenological approach, we study two parameterizations of the effective gravitational coupling, $G_{\mathrm{eff}}$, one based on a Taylor expansion and another linked to the energy density parameter of Dark Energy. We constrain the models with Cosmic Chronometers (CC), Dark Energy Spectroscopic Instrument baryon acoustic oscillations (data release 2), CMB priors, and a gaussian likelihood for the growth index. We show that the constant $\gamma$ approximation is accurate for the parametrization linked to the energy density parameter of dark energy, but presents a non-negligible error for the other case, which we treat as a systematic error in the analysis. We find a $2.4\sigma -3.4\sigma$ tension level with constant $G_{\mathrm{eff}}$, depending on the parametrization. The results indicate that $G_{\mathrm{eff}}<G_N$ around the period of accelerated expansion, corresponding to a weaker effective gravitational interaction on cosmological scales, which leads to a suppression of the growth of cosmological structures.

8 pages, 4 figures, 2 tables

References in corpus (20)

• Models of f(R) Cosmic Acceleration that Evade Solar-System Tests
• Raising the bar: new constraints on the Hubble parameter with cosmic chronometers at z$\sim$2
• Dark Energy after GW170817: dead ends and the road ahead
• Implications of the Neutron Star Merger GW170817 for Cosmological Scalar-Tensor Theories
• Euclid. I. Overview of the Euclid mission
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints
• Maximal freedom at minimum cost: linear large-scale structure in general modifications of gravity
• Toward a Better Understanding of Cosmic Chronometers: A new measurement of H(z) at z~0.7
• DESI 2024 VII: Cosmological Constraints from the Full-Shape Modeling of Clustering Measurements
• The dispersion of growth of matter perturbations in f(R) gravity
• KiDS-Legacy: Cosmological constraints from cosmic shear with the complete Kilo-Degree Survey
• Evidence for suppression of structure growth in the concordance cosmological model
• Cosmic chronometers to calibrate the ladders and measure the curvature of the Universe. A model-independent study
• K-mouflage Cosmology: the Background Evolution
• The Limits of Extended Quintessence
• The linear growth rate of structure in Parametrized Post Friedmannian Universes
• CMB constraints on the early universe independent of late time cosmology
• Classifying Linearly Shielded Modified Gravity Models in Effective Field Theory
• The WiggleZ Dark Energy Survey: constraining the evolution of Newton's constant using the growth rate of structure
• Can dark energy explain a high growth index?