Modifications of gravity generated by a multiplicative coupling of a scalar field to the electromagnetic Lagrangian lead to a breaking of Einstein equivalence principle ( EEPB ) as well as to variations of fundamental constants .
In these theoretical frameworks , deviations of standard values of the fine structure constant , \Delta \alpha / \alpha = \phi , and of the cosmic distance duality relation , D _ { L } ( 1 + z ) ^ { -2 } / D _ { A } = \eta = 1 , where D _ { L } and D _ { A } are the luminosity and angular diameter distances , respectively , are unequivocally linked .
In this paper , we search for cosmological signatures of the EEPB by using angular diameter distance from galaxy clusters , obtained via their Sunyaev-Zeldovich effect ( SZE ) and X-ray observations , and distance modulus of type Ia supernovae ( SNe Ia ) .
The crucial point here is that we take into account the dependence of the SZE/X-ray technique with \phi and \eta .
Our new results show no indication of the EEPB .