New geomagnetic limits on the photon mass and on long-range forces coexisting with electromagnetism

A new geomagnetic limit on the photon mass ${\mathit{m}}_{\gamma }$ is derived from an analysis of satellite measurements of the Earth’s magnetic field H→. The primary effect of a nonzero photon mass is to generate an additional contribution to H→ resembling that from an external source. We find ${\mathit{m}}_{\gamma }$≤8×${10}^{\mathrm{-}16}$ eV/${\mathit{c}}^2$=1×${10}^{\mathrm{-}48}$ g=4×${10}^{\mathrm{-}9}$ ${\mathrm{m}}^{\mathrm{-}1}$. The same data are also used to set new limits on long-range fields coexisting with electromagnetism.