Semilinear Robin Problems with Indefinite Potential and Competition Phenomena

Abstract

We consider semilinear parametric Robin problems driven by the Laplacian plus an indefinite and unbounded potential. In the reaction we have two competing nonlinearities. However, the competition is different from the usual one in “concave-convex” problems. Using a combination of different tools we prove a multiplicity theorem producing seven nontrivial smooth solutions all with sign information (four of constant sign and three nodal).