Radial symmetry of positive entire solutions of a fourth order elliptic equation with a singular nonlinearity

Abstract

The necessary and sufficient conditions for a regular positive entire solution $u$ of the biharmonic equation: \begin{equation} \label{0.1} -Δ^2 u=u^{-p} \;\; \mbox{in ${\mathbb{R}}^N(N\ge 3)$}, \;\; p>1 \end{equation} to be a radially symmetric solution are obtained via the moving plane method (MPM) of a system of equations. It is well-known that for any $a>0$, \eqref{0.1} admits a unique minimal positive entire radial solution ${\underline{u}}_a(r)$ and a family of non-minimal positive entire radial solutions $u_a(r)$ such that $u_a(0)={\underline{u}}_a(0)=a$ and $u_a(r)\ge {\underline{u}}_a(r)$ for $r\in (0,\infty )$. Moreover, the asymptotic behaviors of ${\underline{u}}_a(r)$ and $u_a(r)$ at $r=\infty$ are also known. We will see in this paper that the asymptotic behaviors similar to those of ${\underline{u}}_a(r)$ and $u_a(r)$ at $r=\infty$ can determine the radial symmetry of a general regular positive entire solution $u$ of \eqref{0.1}. The precisely asymptotic behaviors of $u(x)$ and $-\hat{I}”u(x)$ at $|x|=\infty$ need to be established such that the moving-plane procedure can be started. We provide the necessary and sufficient conditions not only for a regular positive entire solution $u$ of \eqref{0.1} to be the minimal entire radial solution, but also for $u$ to be a non-minimal entire radial solution.