Cosmological constraints on time-varying cosmological terms: A study of FLRW universe models with $\Lambda(t)$CDM cosmology

TL;DR

This study investigates a cosmological model with a time-varying cosmological constant, deriving exact solutions and fitting them to observational data, showing consistency with current universe acceleration evidence.

Contribution

It introduces an exact solution for $ ext{Λ}(t)$CDM models with a power-law form and constrains parameters using combined observational datasets.

Findings

The universe exhibits acceleration with a transition redshift around z_tr.

The model fits observational data well, consistent with current acceleration.

Derived parameters align with standard cosmological observations.

Abstract

This paper explores models of the FLRW universe that incorporate a time-varying cosmological term $\Lambda(t)$. Specifically, we assume a power-law form for the cosmological term as a function of the scale factor: $\Lambda(t)=\Lambda_{0} a(t)^{-\alpha}$, where $\Lambda_{0}$ represents the present value of the cosmological term. Then, we derive an exact solution to Einstein's field equations within the framework of $\Lambda(t)$CDM cosmology and determine the best-fit values of the model parameters using the combined $H(z)$ + SNe Ia dataset and MCMC analysis. Moreover, the deceleration parameter demonstrates the accelerating behavior of the universe, highlighting the transition redshift $z_{tr}$, at which the expansion shifts from deceleration to acceleration, with confidence levels of $1-\sigma$ and $2-\sigma$. In addition, we analyze the behavior of the Hubble parameter, jerk parameter, and $Om(z)$ diagnostic. Our analysis leads us to the conclusion that the $\Lambda(t)$CDM model is consistent with present-day observations.