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 Λ CDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (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 ϕ 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 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 that the Λ 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.
Highlights
While extremely successful at describing a wide variety of high- and low-redshift observations [1–5], the ΛCDM model has recently begun to display a number of small cracks [6,7].One of the most tantalizing among these crevices is the so-called “H0 tension”, referring to the discrepancy between two independent estimates of the Hubble constant H0
We discuss the results obtained analysing the datasets described in Section 2 within the context of the three models described in Section 3, which we compare using the Akaike Information Criterion (AIC) described in the same section
We revisited the possibility that the dark energy sector might feature two components: a negative cosmological constant and a component with positive energy density on top
Summary
While extremely successful at describing a wide variety of high- and low-redshift observations [1–5], the ΛCDM model has recently begun to display a number of small cracks [6,7]. The work in [165] considered a very interesting case, where the DE sector consists of a slowly-rolling quintessence field (whose energy density is positive) on top of a negative cosmological constant Such a scenario is extremely interesting from a string theory perspective. Notice that the requirement Ωcc + Ωφ > 0, necessary in order for the Universe to accelerate, prevents us from considering a model where the dark energy sector consists solely of a negative cosmological constant, without the quintessence field on top. The rationale is that string constructions generically predict a large number of light bosons on top of the stable AdS vacua: one can in general be faced with a multi-field quintessence scenario, whose effective behaviour might be phantom (see, e.g., [217–221]) (other possibilities for obtaining an effective phantom component from an underlying scalar field model involve considering modifications to gravity [222–231], couplings between dark energy and dark matter [232–246], particle creation mechanisms [247–256], or invoking scalar fields non-minimally coupled to gravity or with a kinetic term that is non-canonical [257–261]).
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