Analyzing Pantheon SNeIa data in the context of Barrow's variable speed of light

Abstract

We analyze the Combined Pantheon Sample of Type Ia supernovae while allowing the velocity of light to vary as a function of the scale factor $c\propto a^{-\zeta }$, as initiated by Barrow [Phys. Rev. D 59, 043515 (1999)]. The variation in the velocity of light creates an effect akin to the refraction phenomenon which occurs for a wave traveling in a medium with varying speed of wave. We elucidate the role of the local scale of gravitationally-bound regions in assisting the refraction effect to manifest. The refraction effect alters the redshift formulae (Lemaitre, distance-vs-z, luminosity distance-vs-z) and warrants a new analysis of the Pantheon dataset. Upon a reformulation of the distance-redshift relations, we achieve a high-quality fit of the Pantheon dataset to the variable light speed approach; the fit is as robust as that obtained in the standard $\Lambda CDM$ model. We find that the Pantheon dataset is consistent with the variable light speed of the functional form: $a\propto t^{\mu }$ and $c\propto a^{1-1/\mu }$ with (i) the cosmic age $t_0\approx 13.9$ Gy as a free parameter, while $\mu$ is unspecified; and (ii) a monotonic variation in the local scale for gravitationally-bound objects (applicable to the emission sources and the Solar System-based apparatus/observer). Due to the agent in (ii), the high-z portion of the Pantheon dataset would produce an "effective" $H_0$ estimate which is 10 percent lower than the $H_0$ estimate obtained from the low-z portion of the dataset. We offer an alternative interpretation of the accelerating expansion by way of variable speed of light, and as a by-product of the agent uncovered in (ii), a tentative suggestion toward "resolving" the ongoing tension in the Hubble constant estimates.

18 pages, 12 figures