Negative Curves and Elliptic Fibrations on a Special Rational Surface

TL;DR

This paper investigates the degrees and singularities of rational curves on a special rational surface with negative curves, using elliptic fibrations and Cremona transformations, providing explicit formulas and computational tools.

Contribution

It extends previous bifurcation diagrams of Cremona maps to compute degrees and singularities of rational curves on a rational surface using elliptic pencils.

Findings

Derived a closed formula for degrees of rational curves in the bifurcation diagram.

Described positions and multiplicities of singularities of these curves.

Implemented computational methods in Python and Singular for explicit equations.

Abstract

The blown up complex projective plane in the twelve triple points of the dual Hesse arrangement has an infinite number of irreducible rational curves of self-intersection $-1$, for short, $(-1)$-curves. In the preprint version of [Dumnicki, 2019], T. Szemberg et alii tried to keep track of plane rational curves which produce $(-1)$-curves, by applying successively to a straight line compositions taken from three different quadratic Cremona maps preserving the dual Hesse arrangement, in such a way as to produce a diagram of bifurcations. The symmetric aspect of the degrees of curves encoded in the entries of the diagram motivated them to propose the problem of to give a closed formula for the degree of the rational curve at the entry $a_{i,j}$. We solved this problem for a slightly different diagram of bifurcations of the same Cremona maps, which recover and extends the data on degrees of the original diagram. We also are able to describe the position and multiplicites of singularities of each rational curve encoded in the diagram, as well as their equations (implemented in Python and Singular softwares). Our idea is to embed the plane rational curves as components of special elements of elliptic pencils, then apply a closed formula for the degrees of the generic curves of the elliptic pencils of [Puchuri, 2013], and, from this, extract the data of the rational curves on each entry of the diagram.