Revisiting constraints on the photon rest mass with cosmological fast radio bursts

Fast radio bursts (FRBs) have been suggested as an excellent celestial laboratory for testing the zero-mass hypothesis of the photon. In this work, we use the dispersion measure (DM)--redshift measurements of 23 localized FRBs to revisit the photon rest mass $m_{\gamma}$. As an improvement over previous studies, here we take into account the more realistic probability distributions of DMs contributed by the FRB host galaxy and intergalactic medium (IGM) from the IllustrisTNG simulation. To better account for the systematic uncertainty induced by the choices of priors of cosmological parameters, we also combine the FRB data with the cosmic microwave background data, the baryon acoustic oscillation data, and type Ia supernova data to constrain the cosmological parameters and $m_{\gamma}$ simultaneously. We derive a new upper limit of $m_{\gamma}\le3.8\times 10^{-51}\;\rm{kg}$, or equivalently $m_{\gamma}\le2.1 \times 10^{-15} \, \rm{eV/c^2}$ ($m_{\gamma} \le 7.2 \times 10^{-51} \, \rm{kg}$, or equivalently $m_{\gamma}\le4.0 \times 10^{-15} \, \rm{eV/c^2}$) at $1\sigma$ ($2\sigma$) confidence level. Meanwhile, our analysis can also lead to a reasonable estimation for the IGM baryon fraction $f_{\rm IGM}=0.873^{+0.061}_{-0.050}$. With the number increment of localized FRBs, the constraints on both $m_{\gamma}$ and $f_{\rm IGM}$ will be further improved. A caveat of constraining $m_{\gamma}$ within the context of the standard $\Lambda$CDM cosmological model is also discussed.