Multiple positive solutions of nonhomogeneous elliptic systems with strongly indefinite structure and critical Sobolev exponents

In this paper, we study the existence of multiple positive solutions to some Hamiltonian elliptic systems − v = λu + up + εf (x), − u = μv + vq + δg(x) in Ω; u, v > 0 in Ω; u = v = 0 on ∂Ω, where Ω is a bounded domain in RN (N 3); 0 f , g ∈ L∞(Ω); 1/(p + 1) + 1/(q +1) = (N − 2)/N, p, q > 1; λ,μ> 0. Using sub- and supersolution method and based on an adaptation of the dual variational approach, we prove the existence of at least two nontrivial positive solutions for all λ,μ ∈ (0,λ1) and ε, δ ∈ (0, δ0), where λ1 is the first eigenvalue of the Laplace operator − with zero Dirichlet boundary conditions and δ0 is a positive number.  2003 Elsevier Inc. All rights reserved