Seshadri Constants Over Fields Of Characteristic Zero

Abstract

Let $X$ be a smooth projective variety defined over a field $k$ of characteristic $0$ and let $\mathcal{L}$ be a nef line bundle defined over $k$. We prove that if $x\in X$ is a $k$-rational point then the Seshadri constant $\epsilon (X,\mathcal{L},x)$ over $\overline{k}$ is the same as that over $k$. We show, by constructing families of examples, that there are varieties whose global Seshadri constant $\epsilon (X)$ is zero. We also prove a result on the existence of a Seshadri curve with a natural (and necessary) hypothesis.