The propagation of singularities for pseudo-differential operators with self-tangential characteristics (Q913156)

This paper is devoted to the analysis of the propagation of singularities of pseudo-differential operators with characteristics of variable multiplicity. The author assumes that the characteristic set is a union of hypersurfaces tangent of exactly order \(k_ 0\geq 1\) along an involutive submanifold of codimension \(d_ 0\geq 2\). Under a suitable generalized Levi condition the author proves that the wave front set of the solutions is propagating along the union of the Hamiltonian fields of the characteristic surfaces. Some interesting applications concerning the wave operator for uniaxial crystals are given.