Sharp Hardy and Hardy--Sobolev inequalities with point singularities on the boundary

Abstract: We study the Hardy inequality when the singularity is placed on the boundary of a bounded domain in $\mathbb{R}<sup>n$ that satisfies both an interior and exterior ball condition at the singularity. We obtain the sharp Hardy constant $n<sup>2/4$ in case the exterior ball is large enough and show the necessity of the large exterior ball condition. We improve Hardy inequality with the best constant by adding a sharp Sobolev term. We next produce criteria that lead to characterizing maximal potentials that improve Hardy inequality. Breaking the criteria one produces successive improvements with sharp constants. Our approach goes through in less regular domains, like cones. In the case of a cone, contrary to the smooth case, the Sobolev constant does depend on the opening of the cone.