Constraints on the Photon Mass with Fast Radio Bursts
  Fast radio bursts (FRBs) are radio bursts characterized by millisecond durations, high Galactic latitude positions, and high dispersion measures. Very recently, the cosmological origin of FRB 150418 has been confirmed by \cite{kea16}, and FRBs are now strong competitors as cosmological probes. The simple sharp feature of the FRB signal is ideal for them to probe some of the fundamental laws of physics. Here we show that by analyzing the delay time between different frequencies, the FRB data can place stringent upper limits on the rest mass of the photon. For FRB 150418 at $z=0.492$, one can potentially reach $m_{\gamma} \leq 5.2 \times 10^{-47}$ g, which is $10^{20}$ times smaller than the rest mass of electron, and is about $10^3$ times smaller than that obtained using other astrophysical sources with the same method. 
Xue-Feng Wu, Song-Bo Zhang, He Gao, Jun-Jie Wei, Yuan-Chuan Zou,   Wei-Hua Lei, Bing Zhang, Zi-Gao Dai, Peter M\'esz\'aros
astro-ph.HE gr-qc hep-ph