Stability of normal bundles of Brill-Noether curves

Abstract

We prove that the normal bundle of a general Brill-Noether curve of genus $g\ge 1$ and degree $d$ in ${\mathbb{P}}^r$ is semistable if $g=1$ or $g\ge \lceil \frac{5r}{2}\rceil r(r-1)$, or $d$ is larger than an explicit function of $g$ and $r$. We further prove that the normal bundle is in fact stable if $g\ge 2$ and either $g$ or $d$ satisfy slightly stronger bounds. In particular, for each $r$ and $g\ge 1$ (respectively, $g\ge 2$), there are at most finitely many $(d,g)$ for which the normal bundle of the general Brill-Noether curve is not semistable (respectively, stable).

Corrected Proposition 3.3 in characteristic 2, improved the exposition and added references. 36 pages