Cusps in $\mathbb{C}^3$ with prescribed ramification

TL;DR

This paper investigates the structure of value semigroups for certain map germs in complex three-space and explores their implications on the reducibility of Severi varieties, revealing new links with combinatorics and number theory.

Contribution

It introduces a detailed analysis of value semigroups with fixed ramification in $\

Findings

Severi varieties are often reducible for specific semigroups.

Connections established between algebraic geometry and additive combinatorics.

New insights into the structure of cusps in complex three-space.

Abstract

We study value semigroups associated to germs of maps $\mathbb{C} \rightarrow \mathbb{C}^3$ with fixed ramification profiles in a distinguished point. We then apply our analysis to deduce that Severi varieties of unicuspidal rational fixed-degree curves with value semigroup ${\rm S}$ in $\mathbb{P}^3$ are often reducible when ${\rm S}$ is either 1) the semigroup of a generic cusp whose ramification profile is a supersymmetric triple; or 2) a supersymmetric semigroup with ramification profile given by a supersymmetric triple. In doing so, we uncover new connections with additive combinatorics and number theory.