Revisiting the case for a negative cosmological constant from low-redshift data

Authors: Luca Visinelli, Sunny Vagnozzi, Ulf Danielsson Preprint number: UUITP-28/19 Abstract: Persisting tensions between high-redshift and low-redshift precision cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the $\Lambda$CDM model, and in particular might have a negative energy density. Motivated by string theory considerations, wherein consistent AdS background are ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, on top of which we consider a dark energy component with equation of state $w_{\phi}$. 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 $r_{\rm drag}$ as determined by the \textit{Planck} collaboration, and the Hubble constant $H_0$ as determined by the SH0ES program. While a negative cosmological constant remains perfectly consistent with data, we find no evidence for the former, while we find mild indications for an effective phantom dark energy component on top, regardless of the choice of distance anchor. A model comparison analysis performed through the Akaike information criterion reveals the $\Lambda$CDM model is favoured over our negative cosmological constant model. While our results are inconclusive, should tensions between high-redshift and low-redshift data persist with future data, it would be worth reconsidering and further refining our toy negative cosmological constant model.