Multi-point Seshadri constants on ruled surfaces

Abstract

Let $X$ be a surface and let $L$ be an ample line bundle on $X$. We first obtain a lower bound for the Seshadri constant $\varepsilon(X,L,r)$, when $r \ge 3$. We then assume that $X$ is a ruled surface and study Seshadri constants on $X$ in greater detail. We also make precise computations of Seshadri constants on $X$ in some cases.

12 pages; slightly improved Theorem 2.1, new references, minor corrections and changes to exposition; to appear in Proc. Amer. Math. Soc