Galaxy clusters, cosmic chronometers and the Einstein equivalence principle

TL;DR

This paper investigates potential violations of the Einstein equivalence principle through cosmological observations, finding no significant deviations from general relativity using galaxy cluster and cosmic chronometer data.

Contribution

It provides the first comprehensive test linking deviations in the cosmic distance duality relation and fine structure constant variations within modified gravity theories.

Findings

No significant deviation from general relativity detected

Constraints on scalar field coupling to electromagnetism

Supports the validity of Einstein equivalence principle in cosmology

Abstract

The Einstein equivalence principle in the electromagnetic sector can be violated in modifications of gravity theory generated by a multiplicative coupling of a scalar field to the electromagnetic Lagrangian. In such theories, deviations of the standard result for the cosmic distance duality relation, and a variation of the fine structure constant are expected and are unequivocally intertwined. In this paper, we search for these possible cosmological signatures by using galaxy cluster gas mass fraction measurements and cosmic chronometers. No significant departure from general relativity is found regardless of our assumptions about cosmic curvature or a possible depletion factor evolution in cluster measurements.