On existence and phase separation of solitary waves for nonlinear Schrödinger systems modelling simultaneous cooperation and competition

Original · EN

We study the existence of positive bound states for the nonlinear elliptic system cases - Δuᵢ + λᵢ uᵢ = ∑ⱼ₌₁ᵈ βij uⱼ² uᵢ & in Ω u₁ = = ud=0 & on ∂ Ω, cases where d ≥ 2, βij= βji, βii,λᵢ >0, and Ω is either a bounded domain of Rⁿ, or Ω=Rⁿ, with N ≤ 3. In light of its applicability in several physical contexts, the problem has been intensively studied in recent years, and several results concerning existence, multiplicity and qualitative properties of the solutions are available if either βij≤ 0 for every i ≠ j, or βij>0 for every i ≠ j and some additional assumptions are satisfied. On the other hand, only very partial results are known in the case of simultaneous cooperation and competition, that is, when there exist two pairs (i₁,j₁) and (i₂,j₂) such that i₁ ≠ j₁, i₂ ≠ j₂, βᵢ₁ ⱼ₁>0 and βᵢ₂,ⱼ₂<0. In this setting, we provide sufficient conditions on the coupling parameters βij in order to have a positive solution. Our first main results establishes the existence of solutions with at least m positive components for every m ≤ d. Any such solution is a minimizer of the energy functional J restricted on a Nehari-type manifold N. By means of level estimates on the constrained second differential of J on N, we show that, under some additional assumptions, any such minimizer has all nontrivial components. In order to prove this second result, we analyse the phase separation phenomena which involve solutions of the system in a not completely competitive framework.