The embedding theorem in Hurwitz-Brill-Noether Theory

We generalize the Embedding Theorem of Eisenbud-Harris from classical Brill-Noether theory to the setting of Hurwitz-Brill-Noether theory. More precisely, in classical Brill-Noether theory, the embedding theorem states that a general linear series of degree d and rank r on a general curve of genus g is an embedding if r is at least 3. If $f\text{\hspace{0.17em}⁣}:C\to {\mathbb{P}}^1$ is a general cover of degree k, and L is a line bundle on C, recent work of the authors shows that the splitting type of $f_{\ast }L$ provides the appropriate generalization of the pair (r, d) in classical Brill–Noether theory. In the context of Hurwitz-Brill-Noether theory, the condition that r is at least 3 is no longer sufficient to guarantee that a general such linear series is an embedding. We show that the additional condition needed to guarantee that a general linear series |L| is an embedding is that the splitting type of $f_{\ast }L$ has at least three nonnegative parts. This new extra condition reflects the unique geometry of k-gonal curves, which lie on scrolls in ${\mathbb{P}}^r$.