Cuspidal quintics and surfaces with $p_g=0,$ $K^2=3$ and 5-torsion

Abstract

If $S$ is a quintic surface in ${\mathbb{P}}^3$ with singular set $15$ $3$-divisible ordinary cusps, then there is a Galois triple cover $\varphi :X\to S$ branched only at the cusps such that $p_g(X)=4,$ $q(X)=0,$ $K_X^2=15$ and $\varphi$ is the canonical map of $X$. We use computer algebra to search for such quintics having a free action of ${\mathbb{Z}}_5$, so that $X/{\mathbb{Z}}_5$ is a smooth minimal surface of general type with $p_g=0$ and $K^2=3$. We find two different quintics, one of which is the Van der Geer--Zagier quintic, the other is new. We also construct a quintic threefold passing through the $15$ singular lines of the Igusa quartic, with $15$ cuspidal lines there. By taking tangent hyperplane sections, we compute quintic surfaces with singular set $17{\mathsf{A}}_2$, $16{\mathsf{A}}_2$, $15{\mathsf{A}}_2+{\mathsf{A}}_3$ and $15{\mathsf{A}}_2+{\mathsf{D}}_4$.

Exposition improved according to the Referee suggestions. Final version

References in corpus (2)

• Cusps and Codes
• Equations of low-degree Projective Surfaces with three-divisible Sets of Cusps