Topological degree for equivariant gradient perturbations of an unbounded self-adjoint operator in Hilbert space (Q1985675)

The authors present a version of the equivariant gradient degree defined for equivariant gradient perturbations of an equivariant unbounded self-adjoint operator with purely discrete spectrum in Hilbert space. Furthermore, they discuss two possible applications of the main results to Hamiltonian systems and to the Seiberg-Witten equations. The results in this paper are new and interesting and may shed some new light on topological degree methods for nonlinear operators in Hilbert space.