Seshadri-type constants and Newton-Okounkov bodies for non-positive at infinity valuations of Hirzebruch surfaces

TL;DR

This paper investigates Seshadri-type constants and Newton-Okounkov bodies for certain valuations on Hirzebruch surfaces, providing explicit geometric descriptions and classifications of these bodies.

Contribution

It introduces an analogue of Seshadri constants for non-positive at infinity valuations and explicitly computes the vertices of Newton-Okounkov bodies for these cases.

Findings

Newton-Okounkov bodies are quadrilaterals or triangles.

Explicit vertices of these bodies are determined.

Different cases are distinguished based on the geometry.

Abstract

We consider flags $E_\bullet=\{X\supset E\supset \{q\}\}$, where $E$ is an exceptional divisor defining a non-positive at infinity divisorial valuation $\nu_E$ of a Hirzebruch surface $\mathbb{F}_\delta$ and $X$ the surface given by $\nu_E,$ and determine an analogue of the Seshadri constant for pairs $(\nu_E,D)$, $D$ being a big divisor on $\mathbb{F}_\delta$. The main result is an explicit computation of the vertices of the Newton-Okounkov bodies of pairs $(E_\bullet,D)$ as above, showing that they are quadrilaterals or triangles and distinguishing one case from another.