Geometric Hardy inequalities for the sub-elliptic Laplacian on convex domains in the Heisenberg group

Abstract

We prove geometric $L^p$ versions of Hardy's inequality for the sub-elliptic Laplacian on convex domains $Ω$ in the Heisenberg group $\mathbb{H}^n$, where convex is meant in the Euclidean sense. When $p=2$ and $Ω$ is the half-space given by $\langle ξ, ν\rangle > d$ this generalizes an inequality previously obtained by Luan and Yang. For such $p$ and $Ω$ the inequality is sharp and takes the form \begin{equation} \int_Ω|\nabla_{\mathbb{H}^n}u|^2 \, dξ\geq \frac{1}{4}\int_Ω \sum_{i=1}^n\frac{\langle X_i(ξ), ν\rangle^2+\langle Y_i(ξ), ν\rangle^2}{\textrm{dist}(ξ, \partial Ω)^2}|u|^2\, dξ, \end{equation} where $\textrm{dist}(\, \cdot\,, \partial Ω)$ denotes the Euclidean distance from $\partial Ω$.