New insights on a sign-switching $\Lambda$

TL;DR

This paper explores a sign-switching cosmological constant model, examining the effects of different curvature radii in AdS and dS phases, and finds that additional parameters do not significantly improve data fit, offering new insights into cosmological tensions.

Contribution

It introduces a generalized sign-switching $ ext{Lambda}$ model with different curvature radii in AdS and dS phases, analyzing its impact on cosmological data fitting.

Findings

The transition redshift $z_c$ correlates with vacuum energy in AdS phase.

Adding extra parameters does not improve the model fit.

Vacuum energy in dS phase may differ from $- ext{Omega}_{ extLambda_-}$.

Abstract

The proposal for a sudden sign-switching cosmological constant $\Lambda$ in the local universe, emulating a phase transition from anti-de Sitter (AdS) to de Sitter (dS) space, has markedly revamped the fit to observational data and lays out a propitious framework for ameliorating major cosmological tensions, such as the $H_0$ and $S_8$ tensions. This proposal is widely known as $\Lambda_s$CDM. We investigate the possibility that $\Lambda$ does not only flip sign at the transition but has also different curvature radii in the AdS and dS phases. We show that the critical redshift of the transition $z_c$ is strongly correlated with the vacuum energy in the AdS phase $\Omega_{\Lambda_-}$, and that these two variables do not correlate strongly with the other cosmological parameters. We also show that the cost of adding an additional parameter to the $\Lambda_s$CDM cosmological model does not improve the goodness of fit. Armed with our findings, we demonstrate that for a proper choice of $z_c$, the vacuum energy in the dS phase may not necessarily be $-\Omega_{\Lambda_-}$, for comparable degree of conformity between the model prediction and experimental data.