Cosmographic analysis of sign-switching dark energy

Abstract

Inspired by the well-studied ${\Lambda }_{\mathrm{s}}$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 ${\Lambda }_{\mathrm{s}}$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 ${\Lambda }_{\mathrm{s}}$CDM model, replacing it with a milder $w$-singularity.

Comments: Version accepted in PRD. Physical discussion improved and references added. 20 pages, 6 figures, REVTeX 4.2