  We resolve several puzzles related to the electromagnetic response of
topological superconductors in 3+1 dimensions. In particular we show by an
analytical calculation that the interface between a topological and normal
superconductor does not exhibit any quantum Hall effect as long as time
reversal invariance is preserved. We contrast this with the analogous case of a
topological insulator to normal insulator interface. The difference is that in
the topological insulator the electromagnetic vector potential couples to a
vector current in a theory with a Dirac mass, while in the superconductor a
pair of Weyl fermions are gapped by Majorana masses and the electromagnetic
vector potential couples to their axial currents.
