Impact of a negative cosmological constant on the reconstruction of dark energy in light of DESI BAO data

TL;DR

This study explores how a negative cosmological constant influences dark energy's behavior, using DESI BAO data and two reconstruction methods, suggesting a slight preference for a negative cosmological constant and its impact on the dark energy equation of state.

Contribution

It introduces a comparative analysis of the effects of a negative cosmological constant on dark energy reconstruction using DESI data with two distinct methods.

Findings

A negative cosmological constant is slightly favored by data.

Degeneracy affects constraints on dark energy's equation of state.

Phantom divide $w=-1$ becomes more consistent with data.

Abstract

An anti-de Sitter vacuum, corresponding to a negative cosmological constant (NCC), might coexist with one evolving positive dark energy component at low redshift and is hinted by the latest DESI observations. In this paper, we use two methods, \textit{redshift-binned} and \textit{Gaussian Process-based} reconstructions to investigate the effect of a NCC on the equation of state (EOS) $w(z)$ of evolving dark energy (DE) component. We find that a NCC is slightly preferred in both the two reconstructions by up to $\simeq1\sigma$. Although the degeneracy between the EOS of evolving DE component and NCC weakens the constraint on the reconstructed $w(z)$, this degeneracy leads to the phantom divide $w=-1$ more consistent with the 1$\sigma$ posterior of $w(z)$.