Categorical resolutions of cuspidal singularities
Let $X$ be a projective variety of dimension at least two with an isolated $A_2$ singularity. We study its bounded derived category and prove that there exists a crepant categorical resolution $π_*\colon \widetilde{\mathcal{D}} \to D^b(X)$, which is a Verdier localization. More importantly, we give an explicit description of a generating set for its kernel. In the case of an even dimensional variety with a single $A_2$ singularity, we prove that this generating set is given by two $2$-spherical objects. If $X$ is a cubic fourfold with an isolated $A_2$ singularity, we show that this resolution restricts to a crepant categorical resolution $\widetilde{\mathcal{A}}_X$ of the Kuznetsov component $\mathcal{A}_X \subset D^b(X)$, and that $\widetilde{\mathcal{A}}_X$ is equivalent to the bounded derived category of a K3 surface.