English

Virtual signed Euler characteristics

Algebraic Geometry 2024-02-27 v2

Abstract

Roughly speaking, to any space MM with perfect obstruction theory we associate a space NN with symmetric perfect obstruction theory. It is a cone over MM given by the dual of the obstruction sheaf of MM, and contains MM as its zero section. It is locally the critical locus of a function. More precisely, in the language of derived algebraic geometry, to any quasi-smooth space MM we associate its (1)(-1)-shifted cotangent bundle NN. By localising from NN to its C\mathbb C^*-fixed locus MM this gives five notions of virtual signed Euler characteristic of MM: (1) The Ciocan-Fontanine-Kapranov/Fantechi-G\"ottsche signed virtual Euler characteristic of MM defined using its own obstruction theory, (2) Graber-Pandharipande's virtual Atiyah-Bott localisation of the virtual cycle of NN to MM, (3) Behrend's Kai-weighted Euler characteristic localisation of the virtual cycle of NN to MM, (4) Kiem-Li's cosection localisation of the virtual cycle of NN to MM, (5) (1)vd(-1)^{vd} times by the topological Euler characteristic of MM. Our main result is that (1)=(2) and (3)=(4)=(5). The first two are deformation invariant while the last three are not.

Keywords

Cite

@article{arxiv.1408.2541,
  title  = {Virtual signed Euler characteristics},
  author = {Yunfeng Jiang and Richard P Thomas},
  journal= {arXiv preprint arXiv:1408.2541},
  year   = {2024}
}

Comments

Referees' corrections and improvements

R2 v1 2026-06-22T05:25:44.293Z