Tangential limits for harmonic functions with respect to $\phi(\Delta)$ : stable and beyond

Abstract

In this paper, we discuss tangential limits for regular harmonic functions with respect to $\phi(\Delta):=-\phi(-\Delta)$ in the $C^{1,1}$ open set $D$ in $\mathbb{R}^d$, where $\phi$ is the complete Bernstein function and $d \ge 2$. When the exterior function $f$ is local $L^p$-H\"older continuous of order $\beta$ on $D^c$ with $ p\in(1,\infty]$ and $\beta>1/p$, for a large class of Bernstein function $\phi$, we show that the regular harmonic function $u_f$ with respect to $\phi(\Delta)$, whose value is $f$ on $D^c$, converges a.e. through a certain parabola that depends on $\phi$ and $\phi'$. Our result includes the case $\phi(\lambda)=\log(1+\lambda^{\alpha/2})$. Our proofs use both the probabilistic and analytic methods.