# Deformation-obstruction theory for diagrams of algebras and applications to geometry

### Severin Barmeier

Albert-Ludwigs-Universität Freiburg, Germany### Yaël Frégier

Université d'Artois, France

## Abstract

Let $X$ be an algebraic variety over an algebraically closed field of characteristic $0$ and let $Coh(X)$ denote its Abelian category of coherent sheaves. By the work of W. Lowen and M. Van den Bergh, it is known that the deformation theory of $Coh(X)$ as an Abelian category can be seen to be controlled by the Gerstenhaber–Schack complex associated to the restriction of the structure sheaf $O_{X}∣_{U}$ to a cover of affine open sets. We construct an explicit L$_{∞}$ algebra structure on the Gerstenhaber–Schack complex controlling the higher deformation theory of $O_{X}∣_{U}$ or $Coh(X)$ in case $X$ can be covered by two acyclic open sets, giving an explicit deformation-obstruction calculus for such deformations. For smooth $X$, such deformations recover the deformation of complex structures and deformation quantizations of $X$ as degenerate cases, as we show by means of concrete examples.

## Cite this article

Severin Barmeier, Yaël Frégier, Deformation-obstruction theory for diagrams of algebras and applications to geometry. J. Noncommut. Geom. 14 (2020), no. 3, pp. 1019–1047

DOI 10.4171/JNCG/385