📝 SummarXiv

Abstract

We show that a minimally extended varying-speed-of-light (meVSL) cosmology can alleviate the Hubble tension through a single parameter, b. This parameter both shortens the sound horizon at the drag epoch and modifies cosmological time dilation for transients, Delta_t_obs=(1+z)^n Delta_t_emit with n=1-b/4. The reduction in r_d raises the early-universe-inferred H_0 from CMB/BAO analyses, while departures of n from unity provide an independent, time-domain probe of b. Using Fisher forecasts for a DES-like survey, we estimate the supernova sample size required to detect sub-percent deviations in n under realistic statistical and systematic uncertainties. For illustration, b=0.03 yields z_drag = 1108 and r_d = 135 Mpc, consistent with H_0=~73 km/s/Mpc. We conclude that current and upcoming time-domain surveys can place competitive constraints on b and, jointly with CMB/BAO, provide a self-consistent observational test of meVSL's ability to alleviate the H_0 discrepancy.