Generalized Maxwell equations and charge conservation censorship

Abstract: The Aharonov-Bohm electrodynamics is a generalization of Maxwell theory with reduced gauge invariance. It allows to couple the electromagnetic field to a charge which is not locally conserved, and has an additional degree of freedom, the scalar field $S=\partial_\alpha A^\alpha$, usually interpreted as a longitudinal wave component. By re-formulating the theory in a compact Lagrangian formalism, we are able to eliminate $S$ explicitly from the dynamics and we obtain generalized Maxwell equation with interesting properties: they give $\partial_\mu F^{\mu \nu}$ as the (conserved) sum of the (possibly non-conserved) physical current density $j^\nu$, and a "secondary" current density $i^\nu$ which is a non-local function of $j^\nu$. This implies that any non-conservation of $j^\nu$ is effectively "censored" by the observable field $F^{\mu \nu}$, and yet it may have real physical consequences. We give examples of stationary solutions which display these properties. Possible applications are to systems where local charge conservation is violated due to anomalies of the ABJ kind or to macroscopic quantum tunnelling with currents which do not satisfy a local continuity equation.