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_γ. 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_γ simultaneously. We derive a new upper limit of m_γ≤3.8× 10^-51 kg, or equivalently m_γ≤2.1 × 10^-15 eV/c^2 (m_γ≤ 7.2 × 10^-51 kg, or equivalently m_γ≤4.0 × 10^-15 eV/c^2) at 1σ (2σ) confidence level. Meanwhile, our analysis can also lead to a reasonable estimation for the IGM baryon fraction f_ IGM=0.873^+0.061_-0.050. With the number increment of localized FRBs, the constraints on both m_γ and f_ IGM will be further improved. A caveat of constraining m_γ within the context of the standard ΛCDM cosmological model is also discussed.