The Dispersion Relation of Massive Photons in Plasma: A Comment on “Bounding the Photon Mass with Ultrawide Bandwidth Pulsar Timing Data and Dedispersed Pulses of Fast Radio Bursts”

The dispersion measures of fast radio bursts have been identified as a powerful tool for testing the zero-mass hypothesis of the photon. The classical approach treats the massive photon-induced and plasma-induced time delays as two separate phenomena. Recently, Y.-B. Wang et al. suggested that the joint influence of the nonzero photon mass and plasma effects should be considered, and proposed a revised time delay for massive photons propagating in a plasma medium, denoted as Δtmγ′∝ν−4 , which departures from the classical dispersion relation (∝ν ⁻²). Here we discuss the derivation presented by Y.-B. Wang et al. and show that the classical dispersion relation remains valid based on Proca equations.