A weighted Sobolev-Poincar\'e type trace inequality on Riemannian manifolds

Given $(M, g)$ a smooth compact $(n+1)$-dimensional Riemannian manifold with boundary $\partial M$. Let $\rho$ be a defining function of $M$ and $\sigma \in(0,1)$. In this paper we study a weighted Sobolev-Poincar\'e type trace inequality corresponding to the embedding of $W^{1,2}(\rho^{1-2 \sigma}, M) \hookrightarrow L^{p}(\partial M)$, where $p=\frac{2 n}{n-2 \sigma}$. More precisely, under some assumptions on the manifold, we prove that there exists a constant $B>0$ such that, for all $u \in W^{1,2}(\rho^{1-2\sigma}, M)$, $$\Big(\int_{\partial M}|u|^{p} \,\ud s_{g}\Big)^{2/p} \leq \mu^{-1} \int_{M} \rho^{1-2 \sigma}|\nabla_{g} u|^{2} \,\ud v_{g}+B \Big|\int_{\partial M} |u|^{p-2}u \,\ud s_{g}\Big|^{2/(p-1)}.$$ This inequality is sharp in the sense that $\mu^{-1}$ cannot be replaced by any smaller constant. Moreover, unlike the classical Sobolev inequality, $\mu^{-1}$ does not depend on $n$ and $\sigma$ only, but depends on the manifold.