Constraints on Late Time Violations of the Equivalence Principle in the Dark Sector

TL;DR

This paper investigates late-time violations of the equivalence principle in the dark sector, showing current cosmological observations do not strongly constrain such violations, but non-linear regime studies could provide tighter bounds.

Contribution

The study demonstrates that late-time equivalence principle violations in the dark sector are weakly constrained by linear cosmological observations, highlighting the need for non-linear analysis.

Findings

Late-time dark sector EP violations are weakly constrained by linear data

Current cosmological observations do not strongly limit dark sector EP violations

Non-linear regime studies are essential for tighter constraints

Abstract

If dark energy is dynamical due to the evolution of a scalar field, then in general it is expected that the scalar is coupled to matter. While couplings to the standard model particles are highly constrained by local experiments, bounds on couplings to dark matter (DM) are only obtained from cosmological observations and they are consequently weaker. It has recently been pointed out that the coupling itself can become non-zero only at the time of dark energy domination, due to the evolution of dark energy itself, leading to a violation of the equivalence principle (EP) in the dark sector at late times. In this paper we study a specific model and show that such late-time violations of the EP in the DM sector are not strongly constrained by the evolution of the cosmological background and by observables in the linear regime (e.g. from the cosmic microwave background radiation). A study of perturbations in non-linear regime is necessary to constrain late--time violations of the equivalence principle much more strongly.