Photon rest mass from localized fast radio bursts with improved distribution of dispersion measure from extragalactic gas

TL;DR

This paper uses improved models of dispersion measures from extragalactic gas in fast radio bursts to set the most stringent limits yet on the photon rest mass, supporting the photon being massless.

Contribution

It introduces an improved distribution function for extragalactic dispersion measures and applies it across multiple cosmological models to constrain the photon rest mass.

Findings

Most stringent photon mass upper limits from FRBs to date.

Cosmological model choice has minor impact on photon-mass bounds.

Results support the massless photon hypothesis.

Abstract

The assumption that photons are massless is a foundational postulate of modern physics, yet it remains subject to experimental verification. Fast radio bursts (FRBs), with their cosmological distances and precisely measured dispersion, offer an excellent laboratory for testing this hypothesis. In this work, we propose an improved distribution function for the dispersion measure arising from extragalactic gas and demonstrate that it provides an excellent fit to mock data. We then apply this distribution to constrain the photon rest mass under the $\Lambda$CDM, $w$CDM, and $w_{0}w_{a}$CDM cosmological models, the last of which is favored by recent DESI baryon acoustic oscillation observations. The corresponding 1$\sigma$ upper limits on the photon mass are found to be $4.83\times10^{-51}\,\mathrm{kg}$, $4.71\times10^{-51}\,\mathrm{kg}$, and $4.86\times10^{-51}\,\mathrm{kg}$, respectively, which are the most stringent constraints derived from FRBs to date. These results indicate that the choice of cosmological model has only a minor impact on photon-mass bounds, demonstrate that FRBs provide robust and reliable constraints, and offer strong empirical support for the massless nature of the photon.