Indecomposability of derived categories in families

Abstract: Using the moduli space of semiorthogonal decompositions in a smooth projective family introduced by the second, the third and the fourth author, we discuss indecomposability results for derived categories in families. In particular, we prove that given a smooth projective family of varieties, if the derived category of the general fibre does not admit a semiorthogonal decomposition, the same happens for every fibre of the family. As a consequence, we deduce that in a smooth family of complex projective varieties, if there exists a fibre such that the base locus of its canonical linear series is either empty or finite, then any fibre of the family has indecomposable derived category. Then we apply our results to achieve indecomposability of the derived categories of various explicit classes of varieties, as e.g. $n$-fold symmetric products of curves (with $0<n<\lfloor (g+3)/2 \rfloor$), Horikawa surfaces, an interesting class of double covers of the projective plane introduced by Ciliberto, and Hilbert schemes of points on these two classes of surfaces.