In this paper, we establish a new infinite-dimensional linking theorem without (PS)-type assumptions. The new theorem needs a weaker linking geometry and produces bounded (PS) sequences. The abstract result will be applied to the study of the existence of solutions of the strongly indefinite partial differential systems. For the first application, we consider the system
Formula Not Shown where
Ω is a bounded domain in
RN with smooth boundary,
is the outer normal derivative,
H:∂Ω×R×R→R is a positive
C1-function. One nontrivial solution is obtained. The second application, we will solve the eigenvalue problem of the system
Formula Not Shown where
A,
B are self-adjoint operators on
L2(Ω),
Ω
RN is not necessarily bounded;
f,g are Carathéodory functions on
Ω×R2. We get infinitely many solutions. We deal with asymptotically linear cases for both systems.