Existence of solution for two classes of quasilinear systems defined on a non-reflexive Orlicz-Sobolev Spaces
This paper proves the existence of nontrivial solution for two classes of quasilinear systems of the type \begin{equation*} \left\{\; \begin{aligned} -Δ_{Φ_{1}} u&=F_u(x,u,v)+λR_u(x,u,v)\;\text{ in } Ω& \\ -Δ_{Φ_{2}} v&=-F_v(x,u,v)-λR_v(x,u,v)\;\text{ in } Ω& \\ u=v&=0\;\text{ on } \partialΩ& \end{aligned} \right. \end{equation*} where $λ> 0$ is a parameter, $Ω$ is a bounded domain in $\mathbb{R}^N$($N \geq 2$) with smooth boundary $\partial Ω$. The first class we drop the $Δ_2$-condition of the functions $\tildeΦ_i$($i=1,2$) and assume that $F$ has a double criticality. For this class, we use a linking theorem without the Palais-Smale condition for locally Lipschitz functionals combined with a concentration-compactness lemma for nonreflexive Orlicz-Sobolev space. The second class, we relax the $Δ_2$-condition of the functions $Φ_i$($i=1,2$). For this class, we consider $F=0$ and $λ=1$ and obtain the proof based on a saddle-point theorem of Rabinowitz without the Palais-Smale condition for functionals Frechet differentiable combined with some properties of the weak$^*$ topology.