Linear Growth of Matter Perturbations Probed by Redshift-Space Distortions in Interacting $\Lambda(t)$CDM Cosmologies

TL;DR

This paper investigates how interacting dark energy models within a flat DM cosmology affect matter growth, using observational data to constrain the clustering parameter and coupling strength at both background and perturbation levels.

Contribution

It introduces and constrains two phenomenological interaction models in DM cosmology using comprehensive observational data, focusing on linear matter perturbations and growth.

Findings

Estimated S_8 b1 0.026 for both models.

Derived constraints on the coupling parameter .

Analyzed implications for dark energy-dark matter interaction.

Abstract

In the context of a spatially flat $\Lambda(t)$CDM cosmology, we investigate interacting dark energy (IDE) scenarios characterized by phenomenological interaction terms proportional to the Hubble expansion rate and the dark energy density. Our analysis is performed at both the background and linear perturbation levels, with particular emphasis on the evolution of dark matter density fluctuations. Cosmological constraints are derived from a joint analysis of CMB distance priors, Baryon Acoustic Oscillations (BAO), Type Ia supernovae (SNe Ia) from Pantheon+, Redshift-Space Distortions (RSD), and $H(z)$ data from Cosmic Chronometers (CC). Using the linear growth of matter perturbations, we estimate the clustering parameter $S_8$ within IDE extensions of the flat $\Lambda(t)$CDM framework. At the perturbative level, we consider interaction terms of the form $Q_{\text{I}}=\varepsilon a H\bar{\rho}_{\Lambda(t)}$ (Model I) and $Q_{\text{II}}=\varepsilon H\bar{\rho}_{\Lambda(t)}$ (Model II). From the combined dataset, we obtain the constraints $S_8 = 0.870 \pm 0.026$ for Model I and $S_8 = 0.872 \pm 0.026$ for Model II. Finally, we discuss the implications for the coupling parameter $\varepsilon$, taking into account the semi-analytical approximations and observational data employed in this study.