Robin problems with indefinite linear part and competition phenomena

We consider a parametric semilinear Robin problem driven by the Laplacian plus an indefinite potential. The reaction term involves competing nonlinearities. More precisely, it is the sum of a parametric sublinear (concave) term and a superlinear (convex) term. The superlinearity is not expressed via the Ambrosetti-Rabinowitz condition. Instead, a more general hypothesis is used. We prove a bifurcation-type theorem describing the set of positive solutions as the parameter $\lambda >0$ varies. We also show the existence of a minimal positive solution ${\tilde{u}}_{\lambda }$ and determine the monotonicity and continuity properties of the map $\lambda \mapsto \tilde{u}_\lambda$.