Photon Mass Limits from Fast Radio Bursts

TL;DR

This paper discusses how fast radio bursts can be used to set limits on the photon mass by analyzing frequency-dependent delays, considering uncertainties, and suggests future improvements with more redshift measurements.

Contribution

It provides a new constraint on the photon mass using FRB data, accounting for uncertainties, and highlights how future FRB observations can improve these limits.

Findings

Photon mass limit of approximately 1.8 x 10^{-14} eV/c^2 from FRB 150418.

Uncertainties in host galaxy, Milky Way, and IGM modeling affect the constraint.

Lower redshift FRBs could yield better sensitivity to photon mass.

Abstract

The frequency-dependent time delays in fast radio bursts (FRBs) can be used to constrain the photon mass, if the FRB redshifts are known, but the similarity between the frequency dependences of dispersion due to plasma effects and a photon mass complicates the derivation of a limit on $m_\gamma$. The dispersion measure (DM) of FRB 150418 is known to $\sim 0.1$%, and there is a claim to have measured its redshift with an accuracy of $\sim 2$%, but the strength of the constraint on $m_\gamma$ is limited by uncertainties in the modelling of the host galaxy and the Milky Way, as well as possible inhomogeneities in the intergalactic medium (IGM). Allowing for these uncertainties, the recent data on FRB 150418 indicate that $m_\gamma \lesssim 1.8 \times 10^{-14}$eV c$^{-2}$ ($3.2 \times 10^{-50}$kg), if FRB 150418 indeed has a redshift $z = 0.492$ as initially reported. In the future, the different redshift dependences of the plasma and photon mass contributions to DM can be used to improve the sensitivity to $m_\gamma$ if more FRB redshifts are measured. For a fixed fractional uncertainty in the extra-galactic contribution to the DM of an FRB, one with a lower redshift would provide greater sensitivity to $m_\gamma$.