# Revisiting a negative cosmological constant from low-redshift data

## TL;DR

This study investigates the possibility of a negative cosmological constant in the dark energy sector using low-redshift data, finding no evidence for it and favoring the standard Lambda-CDM model, but leaves room for future exploration.

## Contribution

It introduces and tests a negative cosmological constant model inspired by string theory against low-redshift observations, comparing it with the standard Lambda-CDM model.

## Key findings

- No evidence for a negative cosmological constant from current data.
- Mild indications of an effective phantom dark energy component.
- Lambda-CDM model is preferred over the negative cosmological constant model.

## Abstract

Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the $\Lambda$CDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (\textit (i.e.) maximally symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state $w_{\phi}$ on top. We test the consistency of the model against low-redshift Baryon Acoustic Oscillation and Type Ia Supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the \textit{Planck} collaboration, and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant, and mild indications for an effective phantom dark energy component on top. A model comparison analysis reveals the $\Lambda$CDM model is favoured over our negative cosmological constant model. While our results are inconclusive, should low-redshift tensions persist with future data, it would be worth reconsidering and further refining our toy negative cosmological constant model by considering realistic string constructions.