We review two procedures for constructing the vector potential of the electromagnetic field on Kerr spacetime, namely, the classic method of Cohen & Kegeles, yielding $A^\mu$ in a radiation gauge, and the newer method of Frolov et al., yielding $A^\mu$ in Lorenz gauge. We demonstrate that the vector potentials are related by straightforward gauge transformations, which we give in closed form. We obtain a new result for a separable Hertz potential $H^{ \mu \nu}$ such that $A_{ \text{ lor}}^\mu = \nabla_\nu H^{ \mu \nu}$.
Categories: gr-qc hep-th math-ph math.MP