Fractional $p$-Laplacians via Neumann problems in unbounded metric measure spaces

Abstract

We prove well-posedness, Harnack inequality and sharp regularity of solutions to a fractional $p$-Laplace non-homogeneous equation $(-{\Delta }_p{)}^{s}u=f$, with $0<s<1$, $1<p<\infty$, for data $f$ satisfying a weighted $L^{p^{\prime }}$ condition in a doubling metric measure space $(Z,d_Z,\nu )$ that is possibly unbounded. Our approach is inspired by the work of Caffarelli and Silvestre \cite{CS} (see also Mol{č}anov and Ostrovski{ĭ} \cite{MO}), and extends the techniques developed in \cite{CKKSS}, where the bounded case is studied. Unlike in \cite{EbGKSS}, we do not assume that $Z$ supports a Poincaré inequality. The proof is based on the well-posedness of the Neumann problem on a Gromov hyperbolic space $(X,d_X,\mu )$ that arises as an hyperbolic filling of $Z$.

49 pages