Observables in theories with a varying fine structure constant

Abstract

We show how two seemingly different theories with a scalar multiplicative coupling to electrodynamics are actually two equivalent parametrisations of the same theory: despite some differences in the interpretation of some phenemenological aspects of the parametrisations, they lead to the same physical observables. This is illustrated on the interpretation of observations of the Cosmic Microwave Background.Comment: 14 pages, matched published versio

Improved constraints on violations of the Einstein equivalence principle in the electromagnetic sector with complementary cosmic probes

“…In which follows we will present the main results in the case where the electromagnetic field is the only matter field present into the action (1), although it is not a significant source of curvature (photons are just test particles non-minimally coupled to Φ). In the vacuum the Lagrangian is [9] …”

“…In this way, by considering the large class of theories proposed by [7,9] where the relation (14) is valid, we have access to [27] …”

“…According to the Refs. [7,9], the standard CMB temperature evolution law, T CMB (z) = T 0 (1 + z), has been modified to…”

Can galaxy clusters, type Ia supernovae, and the cosmic microwave background rule out a class of modified gravity theories?

“…Recently, a wide class of theories of gravity that explicitly breaks the Einstein equivalence principle (EEP) have been considered in the literature and a powerful mechanism to test its signatures in observable constants of nature has been developed by A. Hees et al [22,23]. They consider models which implements the break of the equivalence principle by introducing an additional term into the action, coupling the usual matter fields Ψ to a new scalar field φ, which is motivated by scalar-tensor theories of gravity, for instance.…”

“…They consider models which implements the break of the equivalence principle by introducing an additional term into the action, coupling the usual matter fields Ψ to a new scalar field φ, which is motivated by scalar-tensor theories of gravity, for instance. The explicit form of the couplings studied by [22,23] are of the type…”