Gauge invariance, semiminimal coupling, and propagating torsion

Abstract

A dynamical theory of torsion is proposed in which the electromagnetic potential is dispensed from minimal coupling, and a "semiminimal" photon-torsion coupling is introduced and physically justified. Local gauge invariance of the total Lagrangian density is preserved in its usual form, provided that torsion is determined by the gradient of a propagating potential. From the field equations we deduce that a polarized macroscopic body is a source of a dipolar torsion field, and that a test body may feel torsion only if polarized. No disagreement is found with the E\"otv\"os-Dicke-Braginskii tests of the equivalence principle.