Cosmological Constraints on $Λ$(t)CDM Models
H. A. P. Macedo, L. S. Brito, J. F. Jesus, M. E. S. Alves
TL;DR
This work tests time-varying vacuum energy within Λ(t)CDM, focusing on the class $\Lambda_g = \frac{\alpha'}{a^2} + \beta H^2 + \lambda_*$ and its three reduced models. The authors derive the background dynamics, including radiation, and obtain analytic $E(z)$ solutions and the vacuum–matter interaction term $\mathcal{Q}(z)$. They constrain the models with Pantheon SNe Ia, cosmic chronometers, and $H_0$ priors from Planck and SH0ES, finding that $\Lambda_1$ is strongly disfavored by Planck priors while $\Lambda_2$ and $\Lambda_3$ remain viable; SH0ES priors provide weaker exclusion of $\Lambda_1$. When applying Planck distance priors to the full $\Lambda_g$ model, the parameters $\alpha$ and $\beta$ are tightly constrained around zero, indicating little time variation of $\Lambda$ and implying compatibility with the standard $\Lambda$CDM scenario within current uncertainties.
Abstract
Problems with the concordance cosmology $Λ$CDM as the cosmological constant problem, coincidence problems and Hubble tension has led to many proposed alternatives, as the $Λ(t)$CDM, where the now called $Λ$ cosmological term is allowed to vary due to an interaction with pressureless matter. Here, we analyze one class of these proposals, namely, $Λ=α'a^{-2}+βH^2+λ_*$, based on dimensional arguments. Using SNe Ia, cosmic chronometers data plus constraints on $H_0$ from SH0ES and Planck satellite, we constrain the free parameters of this class of models. By using the Planck prior over $H_0$, we conclude that the $λ_*$ term can not be discarded by this analysis, thereby disfavouring models only with the time-variable terms. The SH0ES prior over $H_0$ has an weak evidence in this direction. The subclasses of models with $α'=0$ and with $β=0$ can not be discarded by this analysis. Finally, by using distance priors from CMB, the $Λ$ time-dependence was quite restricted.