A Concavity Inequality for Hessian Quotient Equations

Abstract

We prove a concavity inequality for the Hessian quotient operator $\sigma_k/\sigma_{k-1}$ using a change of basis for symmetric polynomials. This removes an additional structural concavity assumption previously imposed in the interior $C^2$ estimate for convex solutions of the $\sigma_k/\sigma_{k-1}$ equation. The method also yields several useful inequalities for elementary symmetric polynomials.