Constraints on $\Lambda(t)$CDM cosmology using Cosmic Chronometers and Supernova data

TL;DR

This study constrains a dynamic vacuum energy model in $\Lambda(t)$CDM cosmology using cosmic chronometers and supernova data, revealing an accelerating universe with a transition redshift around 0.65 and slight deviations from the standard model.

Contribution

It introduces a parameterization of vacuum energy density and constrains it using MCMC analysis with observational data, providing new insights into dark energy dynamics.

Findings

Universe is currently accelerating in expansion.

Transition redshift $z_t$ is approximately 0.65.

Deviations in jerk parameter are within uncertainties.

Abstract

In this manuscript, we investigate the constraints on dynamical vacuum models within the framework of $\Lambda(t)$CDM cosmology by assuming a parameterization of the vacuum energy density as $\rho_{\Lambda}(t)=\rho_{\Lambda 0} \left[1 + \alpha (1 - a)\right]$, where $\rho_{\Lambda 0}$ is the present vacuum density and $\alpha$ is a free parameter. We use 31 cosmic chronometer data points and 1048 Pantheon type Ia supernova samples to constrain the model parameters. Our statistical analysis employs Markov Chain Monte Carlo (MCMC) simulations. We have found that the universe is currently undergoing accelerated expansion, transitioning from a decelerating phase. The transition redshift $z_t=0.65^{+0.03}_{-0.19}$ obtained from the combined CC+SNe dataset is consistent with recent constraints. The total EoS indicates an accelerating phase, with density parameters for matter and vacuum energy exhibiting expected behaviors. The $Om(z)$ diagnostic shows distinct behaviors for different datasets, and the present value of the jerk parameter deviates slightly from the $\Lambda$CDM model but remains consistent within uncertainties. These findings support the dynamic nature of dark energy and provide valuable constraints on the evolution of the universe.