Log-concavity and anti-maximum principles for semilinear and linear elliptic equations

TL;DR

This paper investigates the existence, log-concavity, and qualitative properties of positive solutions to semilinear and linear elliptic equations in bounded domains, emphasizing the role of maximum principles and convexity.

Contribution

It establishes the existence of positive solutions near linear equations and proves log-concavity in strictly convex domains, extending known results with new analytical techniques.

Findings

Positive solutions exist near linear equations.

Solutions are log-concave in strictly convex domains.

Key reliance on maximum principles and a priori estimates.

Abstract

This paper is concerned with existence and qualitative properties of positive solutions of semilinear elliptic equations in bounded domains with Dirichlet boundary conditions. We show the existence of positive solutions in the vicinity of the linear equation and the log-concavity of the solutions when the domain is strictly convex. We also review the standard results on the log-concavity or the more general quasi-concavity of solutions of elliptic equations. The existence and other convergence results especially rely on the maximum principle, on a quantified version of the anti-maximum principle, on the Schauder fixed point theorem, and on some a priori estimates.