Categorical Torelli theorems for higher Picard rank Fano double covers

Abstract

We prove categorical Torelli theorems for four families of Fano double covers with Picard rank greater than 1. Among these is the family of Verra fourfolds. The other three families manifest as double covers of Fano threefolds, branched in anticanonical K3 surfaces. For the three families of threefolds, our proof is based on reducing equivalences between the Kuznetsov components of Fano threefolds in the same deformation family to derived equivalences of their respective K3 branch divisors, and deducing that the resulting isomorphism of branch divisors gives rise to an isomorphism of the Fano threefolds for each family. For Verra fourfolds, we show that an equivalence of their Kuznetsov components induces an isomorphism of the branch divisors using the theory of 2-torsion Brauer classes on K3 surfaces.