Operator Algebras Seminar: Orbifold Euler Characteristics and Equivariant Euler Classes from a K-Homological Viewpoint

Speaker: 向少聪 (华东师范大学)

Time: 2026-03-20 13:00-14:00
Location: 1402, SIMIS

Abstract:

In this talk, we discuss how orbifold Euler characteristics arise in the study of equivariant Euler classes for proper cocompact actions of a discrete group Gamma on a manifold M. We explain that, at the rational level, the equivariant Euler class is determined by the orbifold Euler characteristics of the connected components of the fixed point sets M^L, where L ranges over the finite cyclic subgroups of Gamma. This gives a concrete description of the fixed-point data encoded by the equivariant Euler class and shows that, rationally, no additional higher Euler characteristic appears.