Observational constraints on varying fundamental constants in a minimal CPC model

Abstract

A minimal model based on the Covariant Physical Couplings (CPC) framework for gravity is proposed. The CPC framework is based on the assumptions of a metric-compatible four-dimensional Riemannian manifold where a covariantly conserved stress-energy tensor acts as source of the field equations which are formally the same as Einstein field equations, but where the couplings {G, c, Λ} are allowed to vary simultaneously. The minimal CPC model takes Λ as a genuine constant while c and G vary in an entangled way that is consistent with Bianchi identity and the aforementioned assumptions. The model is constrained using the most recent galaxy cluster gas mass fraction observational data. Our result indicates that the functions c(z) and G (z) = G 0 (c/c 0 ) 4 are compatible with constant couplings for the two different parameterizations of c = c(z) adopted here.

Testing a varying-$Λ$ model for dark energy within CPC framework

“…This possibility was precisely the instance explored by Ref. [5], where this minimal model was constrained by means of the f gas observational window [87,88,89,90,91,92,93]. As it happens, the data fitting disfavours any actual variations of the speed of light c and, consequently, of the gravitational coupling G. In this paper we want to check if this result is confirmed by other observational probes, such as cosmic chronometers-a.k.a H(z) data [94]-and SNe Ia data [95].…”

“…Refs. [5,50,51] emphasized the consequences of the GC for the modified gravity theory described by the CPC framework. In fact, Eq.…”

“…( 33) requires σ = 4, i.e. it is adequate to describing a varying-Λ scenario within CPC (but it is not consistent with a constant Λ, such as the minimal CPC model [5]). Moreover, Eq.…”

“…Refs. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] in the recent literature. This is a rather controversial topic [29,30,31].…”

“…The CPC framework is a modified gravity proposal inspired by Brans-Dicke theory [32,33] that can be understood as a generalization to GR wherein the physical couplings are allowed to co-vary. In a previous paper [5] we have scrutinized the minimal CPC model, a model admitting co-varying c and G while Λ is kept as a genuine constant. The minimal CPC model was constrained via gas mass fraction data-a powerful model agnostic observational prove [87,88,89,90,91,92,93].…”