Constraining Photon Mass by Energy-Dependent Gravitational Light Bending
  In the standard model of particle physics, photons are mass-less particles with a particular dispersion relation. Tests of this claim at different scales are both interesting and important. Experiments in territory labs and several exterritorial tests have put some upper limits on photon mass, e.g. torsion balance experiment in the lab shows that photon mass should be smaller than $1.2\times 10^{-51}\rm g$. In this work, this claim is tested at a cosmological scale by looking at strong gravitational lensing data available and an upper limit of $8.71\times 10^{-39}$g on photon mass was given. Observations of energy-dependent gravitational lensing with not yet available higher accuracy astrometry instruments may constrain photon mass better. 
Lei Qian
astro-ph.CO