Test of the Equivalence Principle in the Dark Sector on Galactic Scales

TL;DR

This paper tests the Einstein Equivalence Principle in the Dark sector using galactic observations, finding no significant deviations from General Relativity but constraining possible violations.

Contribution

It introduces a tensor-scalar theory with dual conformal couplings to test equivalence principle violations in Dark matter and standard matter.

Findings

Data favor opposite sign couplings if violations occur

No significant deviations from General Relativity detected

Constraints on coupling strengths in Dark sector

Abstract

The Einstein Equivalence Principle is a fundamental principle of the theory of General Relativity. While this principle has been thoroughly tested with standard matter, the question of its validity in the Dark sector remains open. In this paper, we consider a general tensor-scalar theory that allows to test the equivalence principle in the Dark sector by introducing two different conformal couplings to standard matter and to Dark matter. We constrain these couplings by considering galactic observations of strong lensing and of velocity dispersion. Our analysis shows that, in the case of a violation of the Einstein Equivalence Principle, data favour violations through coupling strengths that are of opposite signs for ordinary and Dark matter. At the same time, our analysis does not show any significant deviations from General Relativity.