Birational Calabi-Yau threefolds and BPS state counting

Abstract

This paper contains some applications of Bridgeland-Douglas stability conditions on triangulated categories, and Joyce's work on counting invariants of semistable objects, to the study of birational geometry. We introduce the notion of motivic Gopakumar-Vafa invariants as counting invariants of D2-branes, and show that they are invariant under birational transformations between Calabi-Yau threefolds. The result is similar to the fact that birational Calabi-Yau threefolds have the same betti numbers or Hodge numbers.