A search for the variation of speed of light using galaxy cluster gas mass fraction measurements

TL;DR

This study tests whether the speed of light varies with redshift by analyzing galaxy cluster gas mass fractions, cosmic chronometers, and supernova data, finding mostly negligible variation.

Contribution

Introduces a new method combining multiple cosmological measurements to test the invariance of the speed of light across cosmic time.

Findings

Most analyses show no significant variation of the speed of light.

Degeneracy exists between $c$ variation results and gas mass fraction assumptions.

Results depend on the chosen depletion factor and $H_0$ estimates.

Abstract

In this paper, we implement a new method to test the invariance of the speed of light ($c$) as a function of redshift, by combining the measurements of galaxy cluster gas mass fraction, $H(z)$ from cosmic chronometers, and Type-Ia supernovae (SNe Ia). In our analyses, we consider both a constant depletion factor (which corresponds to the ratio by which the cluster gas mass fraction is depleted with respect to the universal baryonic mean) and one varying with redshift. We also consider the influence of different $H_0$ estimates on our results. We look for a variation of $c$, given by $c(z)=c_0(1+c_1z)$. We find a degeneracy between our final results on $c$ variation and the assumptions on the gas mass fraction depletion factor. Most of our analyses indicate negligible variation of the speed of light.