Interior pointwise $C^{1}$ and $C^{1,1}$ regularity of solutions for general semilinear elliptic equation in nondivergence form

Abstract

In this paper, we obtain $C^{1}$ and $C^{1,1}$ regularity of $L^{n}$-viscosity solutions for general semilinear elliptic equation in nondivergence form under some more weaker assumptions, which generalize the result for equations with nonhomogeneous term $f(x)$ to $f(x,u)$. In particular, the nonhomogeneous term $f(x,u)$ is assumed optimally to satisfy unform Dini continuity condition in $u$ and modified $C^{1,1}$ Newtonian potential condition in $x$. For unbounded coefficients, if $a_{ij}$ is $C_{n}^{-1,1}$ at $x_{0}\in\Omega$ with small modulus, $b_{i}\in L^{q}(\Omega)$ for some $q>n$, the solution is $C^{1}$ at $x_{0}$. Furthermore, if $a_{ij},~b_{i}$ are Dini continuous at $x_{0}$, the solution is $C^{1,1}$ at $x_{0}$.