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

N. Mohapi, A. Hees, J. Larena

Published 2015-10-21Version 1

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 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 case of a violation of the Einstein Equivalence Principle, data favour violations through couplings to ordinary and Dark matters of opposite signs. At the same time, General Relativity remains perfectly compatible with observations at a 2-$\sigma$ confidence level.