Eternal vs singular observers in interacting dark energy-dark matter models

TL;DR

This paper explores how different observer perspectives in interacting dark energy-dark matter models affect the perception of cosmological singularities and demonstrates that certain couplings can produce models consistent with observational data, similar to $\\Lambda$CDM.

Contribution

It introduces a framework where dark matter observers perceive a non-singular universe, providing a novel perspective on cosmological singularities in coupled dark sector models.

Findings

Dark matter observers can see a universe without singularities.

Certain conformal/disformal couplings fit observational data as well as $\\Lambda$CDM.

Models with these couplings avoid traditional cosmological singularities.

Abstract

Interacting dark energy-dark matter models have been widely analyzed in the literature in an attempt to find traces of new physics beyond the usual cosmological ($\Lambda$CDM) models. Such a coupling between both dark components is usually introduced in a phenomenological way through a flux in the continuity equation. However, models with a Lagrangian formulation are also possible. A class of the latter assumes a conformal/disformal coupling that leads to a fifth force on the dark matter component, which consequently does not follow the same geodesics as the other (baryonic, radiation, and dark energy) matter sources. Here we analyze how the usual cosmological singularities of the standard matter frame are seen from the dark matter one, concluding that by choosing an appropriate coupling, dark matter observers will see no singularities but a non-beginning, non-ending universe. By considering two simple phenomenological models we show that such a type of coupling can fit observational data as well as the usual $\Lambda$CDM model.