Paracanonical base locus, Albanese morphism, and semi-orthogonal indecomposability of derived categories

Abstract

Motivated by an indecomposability criterion of Xun Lin for the bounded derived category of coherent sheaves on a smooth projective variety $X$, we study the paracanonical base locus of $X$, that is the intersection of the base loci of $\omega_X \otimes P_{\alpha}$, for all $\alpha \in \mathrm{Pic}^0 X$. We prove that this is equal to the relative base locus of $\omega_X$ with respect to the Albanese morphism of $X$. As an application, we get that bounded derived categories of Hilbert schemes of points on certain surfaces do not admit non-trivial semi-orthogonal decompositions. We also have a consequence on the indecomposability of bounded derived categories in families. Finally, our viewpoint allows to unify and extend some results recently appearing in the literature.