Abstract.We consider microhyperbolic equations degenerated precisely on a hyperplane, and study the propagation of the singularities.
IntroductionIn this paper we study the propagation of the singularity for some class of microhyperbolic operators, containing the case of non-involutive characteristics. As for microhyperbolic operators with non-involutive characteristics, there are many papers for the case of order two (c.f. [1,2,4,5,6,10,11,12,14,15]), and some papers for the case of higher orders (c.f. [16,17,18]). In these cases it is well-known that the propagation of the singularity is closely related to the classical theory for ordinary differential equations. In this paper, we generalize such a result, and give a general representation of the elementary solution: It is the composite of holomorphic microlocal operators and quantized contact transformations. As a natural consequence, we obtain the notion of Stokes operators. Such operators were previously known only for a very special case. Using these operators, we can study the branching of the singularity. Note that we do not assume any restrictive conditions for the lower order terms.Let P (x, D) be a microdifferential operator defined at x * = (0; 0, · · · , 0, √ −1) ∈ T * C n of order m, written in the formHere we have written D = (D 2 , · · · , D n ) as usual. Sometimes we also write