Abstract A previous article by some of the authors introduced a Brans-Dicke-like framework wherein the scalar field φ is composed of both G and c which, for this reason, co-vary according to c3/G = constant. In the present paper, we use observational data to constrain the supposed co-varying G and c, under the hypothesis of the validity of the standard Lemaitre formula 1 + z ∼ a−1. The datasets include SN Ia, BAO, and the value of θ extracted from CMB data. A proxy function is demanded for the varying c since the framework does not provide a closed set of equations for computing the functional form of either G or c uniquely. Accordingly, we choose three separate parameterizations for c(z) inspired both by desirable properties of the varying speed of light (VSL) and by successful phenomenological models from the literature—including the one by Gupta (CCC framework). When combined with DESI, Pantheon+ data strongly favor a variable speed of light with more than 3σ confidence level for all parameterizations considered in this paper, whereas Union2.1 suggests no variation of the speed of light. As we shall demonstrate, this apparent discrepancy is due to a strong correlation that emerges between H0 and VSL.
Bezerra-Sobrinho et al. (Fri,) studied this question.