Stability of Serrin-Type Problem for Hessian Equations and Hessian Quotient Equations

In this paper, we investigate the stability of radial symmetry in the solutions to overdetermined problems for Hessian equations and Hessian quotient equations. We prove that if u is a solution to a Hessian equation or Hessian quotient equation in a smooth domain \(\Omega \) $\mathrm{\Omega }$ , with \(u = 0\) $u=0$ on \(\partial \Omega \) $\partial \mathrm{\Omega }$ and |Du| nearly 1 on \(\partial \Omega \) $\partial \mathrm{\Omega }$ , then the domain \(\Omega \) $\mathrm{\Omega }$ is close to a union of several disjoint unit spheres, and u is approximates to radially symmetric functions in these spheres. Moreover, when \(\Omega \) $\mathrm{\Omega }$ is connected, we show that \(\Omega \) $\mathrm{\Omega }$ is close to a unit ball.