Hochschild cohomology and deformations of $\mathbb{P}$-functors

TL;DR

This paper explores the conditions under which split $ ext{P}$-functors become spherical during deformations, linking Hochschild cohomology to the behavior of spherical twists and $ ext{P}$-twists, with applications to K3 surfaces.

Contribution

It generalizes previous results on object cases to $ ext{P}$-functors, providing criteria for sphericity in deformations and connecting Hochschild cohomology with these properties.

Findings

Necessary and sufficient conditions for $ ext{P}$-functors to become spherical during deformation.

Explanation of how spherical twists relate to $ ext{P}$-twists on special fibers.

Application of results to the $ ext{P}$-functor associated with Hilbert schemes of points on K3 surfaces.

Abstract

Given a split $\mathbb{P}$-functor $F:\mathcal{D}^b(X) \to \mathcal{D}^b(Y)$ between smooth projective varieties, we provide necessary and sufficient conditions, in terms of the Hochschild cohomology of $X$, for it to become spherical on the total space of a deformation of $Y$, and explain how the spherical twist becomes the $\mathbb{P}$-twist on the special fibre. These results generalise the object case, that is when $X$ is a point, which was studied previously by Huybrechts and Thomas, and we show how they apply to the $\mathbb{P}$-functor associated to the Hilbert scheme of points on a K3 surface. In the appendix we review and reorganise some technical results due to Toda, relating to the interaction of Atiyah classes, the HKR-isomorphism, and the characteristic morphism.