Can dark energy explain a high growth index?

Abstract

A promising way to test the physics of the accelerated expansion of the Universe is by studying the growth rate of matter fluctuations, which can be parametrized by the matter energy density parameter to the power $\gamma$, the so-called growth index. It is well-known that the $\Lambda$CDM cosmology predicts $\gamma =0.55$. However, using observational data, Nguyen et al. (2023) measured a much higher $\gamma =0.633_{-0.024}^{+0.025}$, excluding the $\Lambda$CDM value within $3.7\sigma$. In this work, we analyze whether Dark Energy (DE) with the Equation of State (EoS) parameter described by the CPL parametrization can significantly modify $\gamma$ with respect to the predicted $\Lambda$CDM one. Besides the usual Smooth DE (SDE) scenario, where DE perturbations are neglected on small scales, we also consider the case of Clustering Dark Energy (CDE), which has more potential to impact the growth of matter perturbations. In order to minimally constrain the background evolution and assess the largest meaningful $\gamma$ distribution, we use data from $32$ Cosmic Chronometers, $H(z$), data points. In this context, we found that both SDE and CDE models described by the CPL parametrization have almost negligible probability of providing $\gamma >0.6$. However, given that the measured $\gamma$ value assumes the $\Lambda$CDM background, a direct statistical measure of the incompatibility between theory and the measured value can not be done for other backgrounds. Thus, we devise a method in order to make a quick estimation of the $\gamma$ constraints for CPL background. This method indicates that, when using DESI DR2 BAO data to constrain background parameters, no significant changes in the $\gamma$ central value and uncertainty is observed. (Abridged)

13 pages, 10 figures, matches the PRD version

References in corpus (14)

• Cosmology and the Fate of Dilatation Symmetry
• A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team
• Raising the bar: new constraints on the Hubble parameter with cosmic chronometers at z$\sim$2
• The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters
• The Effective Theory of Quintessence: the w<-1 Side Unveiled
• Toward a Better Understanding of Cosmic Chronometers: A new measurement of H(z) at z~0.7
• Arbitrating the $S_8$ discrepancy with growth rate measurements from Redshift-Space Distortions
• Evidence for suppression of structure growth in the concordance cosmological model
• Fingerprinting dark energy
• Cosmic chronometers to calibrate the ladders and measure the curvature of the Universe. A model-independent study
• $S_8$ increases with effective redshift in $\Lambda$CDM cosmology
• A short review on clustering dark energy
• Planck-PR4 anisotropy spectra show (better) consistency with General Relativity
• Spherical collapse of non-top-hat profiles in the presence of dark energy with arbitrary sound speed

Cited by in corpus (1)

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