Morrey-Campanato estimates for Helmholtz equations with two unbounded media

To appear in Proceedings of the Royal Society of Edinburgh AInternational audienceWe prove uniform Morrey-Campanato estimates for Helmholtz equations in the case of two unbounded inhomogeneous media separated by an interface. They imply weighted $L^2$-estimates for the solution. We prove also a uniform $L^2$-estimate {\em without weight} for the trace of the solution on the interfac