## University of Sydney Algebra Seminar

# Bryan Wang (Australian National University)

## Wednesday 9 February, 12.05-12.55pm, Carslaw 535

### Stringy product on orbifold K-theory

Motivated by orbifold string theory models in physics, Chen and Ruan discovered a new product called the stringy product on the cohomology for the inertia orbifold of an almost complex orbifold. This cohomology with the stringy product is now called the Chen-Ruan cohomology, as a classical limit of orbifold quantum cohomology theory. Later, various versions of stringy product on orbifold K-theory of the inertia orbifold were proposed. In a recent joint work with Hu, we define a stringy product on the orbifold K-theory for the orbifold itself and show that a modified de-localized Chern character to the Chen-Ruan cohomology is an isomorphism over the complex coefficient. As an application, we find a new product on the equivariant K-theory of a finite group with the conjugation product, which is different to the well-known Pontryajin (or fusion) product.