The multiplicity of cyclic coverings of a singularity of an algebraic variety

Toya Kumagai, Tomohiro Okuma

Published 2024-03-21Version 1

Let $V$ be an affine algebraic variety, and let $p\in V$ be a singular point. For a regular function $g$ on $V$ such that $g(p)=0$ and for a positive integer $n$, we consider the cyclic covering $\phi_n\: V_n \to V$ of degree $n$ branched along the hypersurface defined by $g$. We will prove that for sufficiently large $n$, the tangent cone of $V_n$ at $\phi_n^{-1}(p)$ is, as an affine variety, the product of the tangent cone of the branch locus and the affine line. In particular, the multiplicity of the singularity $\phi_n^{-1}(p) \in V_n$, which is a function of $n$ determined by $V$ and $g$, remains constant for sufficiently large $n$. This result generalizes Tomaru's theorem for normal surface singularities.