Cosmological perturbations for smooth sign-switching dark energy models

TL;DR

This paper analyzes cosmological models with smooth or abrupt sign changes in the cosmological constant, studying their perturbations and comparing predictions with observational data to understand their viability.

Contribution

It provides a comprehensive perturbative analysis of sign-switching dark energy models, including smooth and abrupt transitions, and compares their predictions with standard cosmology and observations.

Findings

Different models show distinct perturbation behaviors.

Some models can fit observational data similarly to $ ext{Lambda}$CDM.

The smooth sign change models are viable alternatives to standard dark energy.

Abstract

In this work, we carry out a comprehensive perturbative analysis of four cosmological models featuring a sign-switching cosmological constant. Among these, we include the well-known $\Lambda_{\rm s}$CDM model, characterised by an abrupt transition from a negative to a positive cosmological constant. We also consider the L$\Lambda$CDM model, which exhibits a generalised ladder-step evolution, as well as the SSCDM and ECDM models, both of which undergo a smooth sign change at comparable redshifts. We solve the linear cosmological perturbation equations from the radiation-dominated era, imposing initial adiabatic conditions for matter and radiation, for modes well outside the Hubble radius in the early Universe. We analyse the behaviour of the matter density contrast, the gravitational potential, the linear growth rate, the matter power spectrum, and the $f\sigma_8$ evolution . These results are contrasted with predictions from the standard $\Lambda$CDM model and are confronted with observational data.