Observational constraints on cosmological future singularities

TL;DR

This paper investigates future cosmological singularities in dark energy models, analyzing their physical implications and using observational data to constrain the timing of such singularities, finding they are at least 2.8 billion years away.

Contribution

It introduces phenomenological parameterizations of the Hubble rate to model future singularities and constrains their occurrence using observational cosmological data.

Findings

Singularities are at least 2.8 billion years in the future.

Certain parameterizations exclude singularities occurring sooner than 1.2 times the universe's age.

Physical analysis clarifies when singularities correspond to actual spacetime singularities.

Abstract

In this work we consider a family of cosmological models featuring future singularities. This type of cosmological evolution is typical of dark energy models with an equation of state violating some of the standard energy conditions (e.g. the null energy condition). Such kind of behavior, widely studied in the literature, may arise in cosmologies with phantom fields, theories of modified gravity or models with interacting dark matter/dark energy. We briefly review the physical consequences of these cosmological evolution regarding geodesic completeness and the divergence of tidal forces in order to emphasize under which circumstances the singularities in some cosmological quantities correspond to actual singular spacetimes. We then introduce several phenomenological parameterizations of the Hubble expansion rate to model different singularities existing in the literature and use SN Ia, BAO and H(z) data to constrain how far in the future the singularity needs to be (under some reasonable assumptions on the behaviour of the Hubble factor). We show that, for our family of parameterizations, the lower bound for the singularity time can not be smaller than about 1.2 times the age of the universe, what roughly speaking means about 2.8 Gyrs from the present time.