In this paper, we present geometric Hardy inequalities for the sub-Laplacian in half-spaces of stratified groups. As a consequence, we obtain the following geometric Hardy inequality in a half-space of the Heisenberg group with a sharp constant:
∫ℍ+|∇Hu|pdξ≥(p−1p)p∫ℍ+𝒲(ξ)pdist(ξ,∂ℍ+)p|u|pdξ,p>1,
which solves a conjecture in the paper [S. Larson, Geometric Hardy inequalities for the sub-elliptic Laplacian on convex domain in the Heisenberg group, Bull. Math. Sci. 6 (2016) 335–352]. Here, 𝒲(ξ)=(n∑i=1〈Xi(ξ),ν〉2+〈Yi(ξ),ν〉2)12
is the angle function. Also, we obtain a version of the Hardy–Sobolev inequality in a half-space of the Heisenberg group: (∫ℍ+|∇Hu|pdξ−(p−1p)p∫ℍ+𝒲(ξ)pdist(ξ,∂ℍ+)p|u|pdξ)1p≥C(∫ℍ+|u|p∗dξ)1p∗,
where dist(ξ,∂ℍ+) is the Euclidean distance to the boundary, p∗:=Qp/(Q−p), and 2≤p<Q. For p=2, this gives the Hardy–Sobolev–Maz’ya inequality on the Heisenberg group.