Date: 
August 4, Monday, 2008, 13:00  14:30 & 15:30  17:00 
Place: 
Seminar Room at IPMU Prefab. B, Kashiwa Campus of the University of Tokyo 
Speaker: 
Nagao Kentaro (Kyoto University) 
Title: 
Counting invariants of perverse coherent systems on CY 3folds and their wallcrossings

Abstract: 
A perverse coherent system on a CY 3fold is a pair of perverse
coherent sheaf on the CY 3fold and a morphism to it from the
structure sheaf.
We intruduce moduli spaces of perverse coherent systems and counting
invariants of them.
In order to construct a moduli space we should choose a parameter of stability.
We show that DonaldsonThomas theory and PandharipandeThomas theory
can be recovered at specific parameters.
We also establish wallcrossing formulas for the generating functions
of counting invariants of perverse coherent systems.
As applications, we provide some formulas on DT invariants and PT invariants.
