Probing minicharged particles with tests of Coulomb's law.

Minicharged particles arise in many extensions of the standard model. Their contribution to the vacuum polarization modifies Coulomb's law via the Uehling potential. In this Letter, we argue that tests for electromagnetic fifth forces can therefore be a sensitive probe of minicharged particles. In the low mass range < or approximately equal to microeV existing constraints from Cavendish type experiments provide the best model-independent bounds on minicharged particles.