On linear stability and syzygy stability

Abstract

In previous works, the authors investigated the relationships between linear stability of a generated linear series |V| on a curve C, and slope stability of the syzygy vector bundle $$M_{V,L} := \ker (V \otimes \mathcal {O}_C \rightarrow L)$$ M V , L : = ker ( V ⊗ O C → L ) . In particular, the second named author and L. Stoppino conjecture that, for a complete linear system |L|, linear (semi)stability is equivalent to slope (semi)stability of $$M_{L}$$ M L . The first and third named authors proved that this conjecture holds in the two opposite cases: hyperelliptic and generic curves. In this work we provide a counterexample to this conjecture on any smooth plane curve of degree 7.