Photon mass
Abstract

A novel experimental approach based on a toroid Cavendish balance is used to evaluate the product of photon mass squared and the ambient cosmic magnetic vector potential A. The method is based on the energy density of the vector potential in the presence of photon mass, not on measurement of magnetic field. The experiment discloses A m_g² less than 2 x10^-9 Tm/m², with m_g^-1 as the characteristic length associated with photon mass. Consequently if the ambient magnetic vector potential is A approximately 10¹² Tm due to cluster level fields, m_g^-1 is greater than 2 x 10¹⁰ m. If we conservatively use galactic fields prior to a reversal, then m_g^-1 is greater than 1 x 10⁹ m, a figure still superior to that derived from the Jovian magnetic field.

Blurb: PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 361, March 4, 1998 by Phillip F. Schewe and Ben Stein.

Blurb from Science Now on a later, more sensitive experiment. "New Experimental Limit on the Photon Rest Mass with a Rotating Torsion Balance", Jun Luo, Liang-Cheng Tu, Zhong-Kun Hu, and En-Jie Luan, Physical Review Letters, 081801, 26 February 2003