Some cosmological consequences of a breaking of the Einstein equivalence principle

TL;DR

This paper explores how breaking the Einstein Equivalence Principle through scalar-electromagnetic coupling affects cosmological observables, linking variations in fundamental constants with observable deviations in the CMB and distance measures.

Contribution

It establishes a theoretical framework connecting violations of the equivalence principle to observable cosmological effects and derives constraints using current data.

Findings

Stringent bounds on violations of the distance-duality relation.

Constraints on the evolution of the CMB temperature.

Limits on CMB spectral distortions from fine structure constant measurements.

Abstract

In this communication, we consider a wide class of extensions to General Relativity that break explicitly the Einstein Equivalence Principle by introducing a multiplicative coupling between a scalar field and the electromagnetic Lagrangian. In these theories, we show that 4 cosmological observables are intimately related to each other: a temporal variation of the fine structure constant, a violation of the distance-duality relation, the evolution of the cosmic microwave background (CMB) temperature and CMB spectral distortions. 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 spectral distortions using current constraints on the fine structure constant. Alternatively, this offers interesting possibilities to test a wide range of theories of gravity by analyzing several data sets concurrently.