Very general monomial valuations of $\mathbb{P}^2$ and a Nagata type conjecture

Marcin Dumnicki, Brian Harbourne, Alex Küronya, Joaquim Roé, Tomasz Szemberg

Published 2013-12-19, updated 2016-02-05Version 2

It is well known that multi-point Seshadri constants for a small number $s$ of points in the projective plane are submaximal. It is predicted by the Nagata conjecture that their values are maximal for $s\geq 9$ points. Tackling the problem in the language of valuations one can make sense of $s$ points for any positive real $s\geq 1$. We show somewhat surprisingly that a Nagata-type conjecture should be valid for $s\geq 8+1/36$ points and we compute explicitly all Seshadri constants (expressed here as the asymptotic maximal vanishing element) for $s\leq 7+1/9$.