ON THE IRREDUCIBLE COMPONENTS OF SOME BRILL-NOETHER LOCI OF RANK-TWO, STABLE BUNDLES OVER A GENERAL ν-GONAL CURVE

In this paper we consider Brill-Noether loci of rank-two, stable vector bundles of given degree d, with speciality 2 and 3, on a general ν-gonal curve C of genus g with the aim of studying their irreducible components in the whole range of interest for d, namely 2g−2≤d≤4g−4. For speciality 2, either we prove that such a Brill-Noether locus is empty or we completely classify all of its irreducible components, giving also some extra information about their dimensions (exhibiting both regular and superabundant components), about their birational geometry as well as giving precise description of their general point. Similarly, in speciality 3, either we prove that such a Brill-Noether locus is empty or we exhibit irreducible components of several types according to their regularity or superabundance but also according to the precise descriptions of their general points, proving e.g. that in some degrees d there are more than one superabundant component together with the presence of also a regular component. We moreover give extra information about the birational geometry of the constructed components as well as about their local behavior. As a by-product of our general results, we deduce also some consequences on Brill-Noether loci in rank two with fixed general determinant line bundle instead of fixed degree.