Bounding the number of graph refinements for Brill-Noether existence

Abstract

Let $G$ be a finite graph of genus $g$. Let $d$ and $r$ be non-negative integers such that the Brill-Noether number is non-negative. It is known that for some $k$ sufficiently large, the $k$-th homothetic refinement $G^{(k)}$ of $G$ admits a divisor of degree $d$ and rank at least $r$. We use results from algebraic geometry to give an upper bound for $k$ in terms of $g,d,$ and $r$.

arXiv comment10 pages, 2 figures; v2: minor changes throughout, final version, to appear in Eur. J. Math