English

Derived Kodaira Spencer map, Cosection lemma, and semiregularity

Algebraic Geometry 2009-03-30 v2 Commutative Algebra

Abstract

The cosection lemma proved by J. Li and Y.H. Kiem said the intrinsic normal cone lies inside the kernel of any cosection of the obstruction sheaf when the moduli has a perfect obstruction theory. With a definition of higher tangent vectors of a scheme at a point, and a construction of the derived Kodaira Spencer map by K. Behrend and B. Fantechi, we prove a derived version of cosection lemma without perfect obstruction theory condition. As an application we give a short proof of the Kodaira's Principle \textit{ambient cohomology annihilates obstruction} (semiregularity), assuming the existence of locall universal family.

Keywords

Cite

@article{arxiv.0808.0988,
  title  = {Derived Kodaira Spencer map, Cosection lemma, and semiregularity},
  author = {Huai-Liang Chang},
  journal= {arXiv preprint arXiv:0808.0988},
  year   = {2009}
}

Comments

10 pages

R2 v1 2026-06-21T11:08:23.483Z