A. We 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. Two possible applications are discussed.
ITo obtain new bifurcation results, N. Dancer [5] introduced in 1985 a new topological invariant for S 1 -equivariant gradient maps, which provides more information than the usual equivariant one. In 1994 S. Rybicki [14,16] developed the complete degree theory for S 1 -equivariant gradient maps and 3 years later K. Gęba extended this theory to an arbitrary compact Lie group. In 2001 S. Rybicki [15] defined the degree for S 1 -equivariant strongly indefinite functionals in Hilbert space. 10 years later A. Gołębiewska and S. Rybicki [8] generalized this degree to compact Lie groups. The relation between equivariant and equivariant gradient degree theories were studied in [1,2,7].The main goal of this paper is to present a construction and properties of a new degree-type topological invariant Deg ∇ G , which is defined for equivariant gradient perturbations of a equivariant unbounded self-adjoint Hilbert operator with a purely discrete spectrum (in the general case a compact Lie group). As far as we know, the idea of the construction of such an invariant should be attributed to K. Gęba.It is worth pointing out that equivariant gradient perturbations of an equivariant unbounded self-adjoint operator with a purely discrete spectrum appear naturally in a variety of problems in nonlinear analysis, such as the search for periodic solutions of Hamiltonian systems Date: December 24, 2018.