Non-Hamiltonian Actions and Lie-Algebra Cohomology of Vector Fields

Abstract

Two examples of Diff⁺S¹-invariant closed two-forms obtained from forms on jet bundles, which does not admit equivariant moment maps are presented. The corresponding cohomological obstruction is computed and shown to coincide with a nontrivial Lie algebra cohomology class on H²(X(S¹)).