Breaking of the equivalence principle in the electromagnetic sector and its cosmological signatures

TL;DR

This paper investigates how modifications of gravity involving a scalar field coupled to electromagnetism can cause observable cosmological effects, linking variations in fundamental constants to potential violations of established cosmological relations.

Contribution

It establishes a systematic framework connecting scalar field modifications to observable cosmological signatures and derives constraints from current data.

Findings

Stringent constraints on violations of the distance duality relation.

Constraints on the evolution of the CMB temperature.

Predictions for future data from EUCLID and SKA.

Abstract

This paper proposes a systematic study of cosmological signatures of modifications of gravity via the presence of a scalar field with a multiplicative coupling to the electromagnetic Lagrangian. We show that, in this framework, variations of the fine structure constant, violations of the distance duality relation, evolution of the cosmic microwave background (CMB) temperature and CMB distortions are intimately and unequivocally linked. This enables one to put very stringent constraints on possible violations of the distance duality relation, on the evolution of the CMB temperature and on admissible CMB distortions using current constraints on the fine structure constant. Alternatively, this offers interesting possibilities to test a wide range of theories of gravity by analysing several datasets concurrently. We discuss results obtained using current data as well as some forecasts for future data sets such as those coming from EUCLID or the SKA.