Galaxy clusters, cosmic chronometers and the Einstein equivalence
  principle
  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.
