Brill-Noether loci of pencils with prescribed ramification on moduli of curves and on severi varieties on $K3$ surfaces

Under the assumption that the adjusted Brill-Noether number ρ is at least $-g$ , we prove that the Brill-Noether loci in Mg,n of pointed curves carrying pencils with prescribed ramification at the marked points have a component of the expected codimension with pointed curves having Brill-Noether varieties of pencils of the minimal dimension. As an application, the map from the Hurwitz scheme to Mg is dominant if n+ ρ ≥ 0 and generically finite otherwise, settling a variation of a classical problem of Zariski. In the second part of the paper, we study the analogous loci of curves in Severi varieties on $K3$ surfaces, proving existence of curves with nongeneral behaviour from the point of view of Brill-Noether theory. This extends previous results of Ciliberto and the first-named author to the ramified case. We apply these results to study correspondences and cycles on $K3$ surfaces in relation to Beauville-Voisin points and constant cycle curves.