Do cosmological observations allow a negative $\Lambda$?

TL;DR

This paper investigates whether current cosmological data support the existence of a negative cosmological constant, finding that models with negative $ ext{Lambda}$ are compatible and sometimes preferred over the standard $ ext{Lambda}$CDM model.

Contribution

It introduces and tests quintessence models with negative $ ext{Lambda}$ against observational data, showing their viability and potential preference over $ ext{Lambda}$CDM.

Findings

Negative $ ext{Lambda}$ models are compatible with current data.

Such models are sometimes preferred over $ ext{Lambda}$CDM.

Negative $ ext{Lambda}$ can naturally arise in string theory.

Abstract

In view of the recent measurement of $H_{0}$ from HST and SH0ES team, we explore the possibility of existence of a negative cosmological constant (AdS vacua in the dark energy sector) in the Universe. In this regard, we consider quintessence fields on top of a negative cosmological constant and compare such construction with $\Lambda$CDM model using a different combination of CMB, SnIa, BAO and $H_{0}$ data. Various model comparison estimators show that quintessence models with a negative $\Lambda$ is either preferred over $\Lambda$CDM or performs equally as $\Lambda$CDM model. This suggests that the presence of a negative $\Lambda$ (AdS ground state) in our Universe, which can naturally arise in string theory, is consistent with cosmological observations.