Green function estimates for subordinate Brownian motions : stable and beyond

Abstract

A subordinate Brownian motion $X$ is a L\'evy process which can be obtained by replacing the time of the Brownian motion by an independent subordinator. In this paper, when the Laplace exponent $\phi$ of the corresponding subordinator satisfies some mild conditions, we first prove the scale invariant boundary Harnack inequality for $X$ on arbitrary open sets. Then we give an explicit form of sharp two-sided estimates on the Green functions of these subordinate Brownian motions in any bounded $C^{1,1}$ open set. As a consequence, we prove the boundary Harnack inequality for $X$ on any $C^{1,1}$ open set with explicit decay rate. Unlike {KSV2, KSV4}, our results cover geometric stable processes and relativistic geometric stable process, i.e. the cases when the subordinator has the Laplace exponent $$\phi(\lambda)=\log(1+\lambda^{\alpha/2}) (0<\alpha\leq 2, d > \alpha)$$ and $$\phi(\lambda)=\log(1+(\lambda+m^{\alpha/2})^{2/\alpha}-m) (0<\alpha<2,\, m>0, d >2) .$$