Nonlinear nonlocal Douglas identity

Abstract

We give Hardy-Stein and Douglas identities for nonlinear nonlocal Sobolev-Bregman integral forms with unimodal Lévy measures. We prove that the corresponding Poisson integral defines an extension operator for the Sobolev-Bregman spaces. We also show that the Poisson integrals are quasiminimizers of the Sobolev-Bregman forms.

29 pages; we added applications to the Dirichlet-to-Neumann map, in Section 6