Gradient and Hessian regularity in elliptic transmission problems near a point cusp

We consider elliptic transmission problems in several space dimensions near an interface which is C1,1 diffeomorphic to an axisymmetric reference-interface with a singular point of cusp type. We establish the regularity of the gradient and of the Hessian in Lᵖ spaces up to the cusp point for local weak solutions. We obtain regularity thresholds which are different according to whether the cusp is inward or outward to the subdomain, and which depend explicitly on the opening of the interface at the cusp. Our results allow for source terms in the bulk and on the interface.