Cosmographic analysis of sign-switching dark energy

TL;DR

This paper introduces and analyzes dynamical dark energy models where the cosmological constant transitions from negative to positive, using cosmography and statefinder parameters, and compares them with standard models.

Contribution

It proposes new models with sign-changing cosmological constants and studies their properties and singularities using cosmographic methods.

Findings

Sign change removes sudden singularity present in previous models.

Models exhibit milder $w$-singularity after sign change.

Comparison shows differences from standard $ ull$LambdaCDM models.

Abstract

Inspired by the well-studied $\Lambda_{\rm s}$CDM model, we propose and investigate a class of dynamical dark energy models that evolve from a negative cosmological constant, transitioning to a positive value at low redshifts. Specifically, we introduce a dark energy framework based on a generalised ladder-step function for the cosmological constant. Furthermore, we present two additional models in which the cosmological constant undergoes a smooth sign change at a specified redshift. We provide a detailed discussion of the construction and theoretical properties of these models, analysing their background cosmological evolution using a cosmographic approach and the statefinder hierarchy parameters. Our results are compared with those obtained for the standard $\Lambda$CDM and $\Lambda_{\rm s}$CDM models. We also perform a careful analysis of the types of singularities that may arise in these models due to a sign change in the cosmological constant. Notably, we show that a continuous sign change removes the sudden singularity present in the $\Lambda_{\rm s}$CDM model, replacing it with a milder $w$-singularity.