  Due to spectral obstructions, a scattering theory in the Lax-Phillips sense
for the wave equation for differential p-forms on H^{n+1} cannot be developed.
As a consequence, Huygens' principle for the wave equation in this context does
not hold. If we restrict the class of forms and we consider the case of
coclosed p-forms on H^{n+1}, when n=2p, Huygens' principle does hold and thus
in this case incoming and outgoing subspaces can be constructed.
