Morse Theory and the topology of holomorphic foliations near an isolated singularity

Abstract

Let $\mathcal{F}$ be the germ at $0\in {\mathbb{C}}^n$ of a holomorphic foliation of dimension $d$, $1\le d<n$, with an isolated singularity at $0$. We study its geometry and topology using ideas that originate in the work of Thom concerning Morse theory for foliated manifolds. Given $\mathcal{F}$ and a real analytic function $g$ on ${\mathbb{C}}^n$ with a Morse critical point of index 0 at $0$, we look at the corresponding polar variety $M=M(\mathcal{F},g)$. These are the points of contact of the two foliations, where $\mathcal{F}$ is tangent to the fibres of $g$. This is analogous to the usual theory of polar varieties in algebraic geometry, where holomorphic functions are studied by looking at the intersection of their fibers with those of a linear form. Here we replace the linear form by a real quadratic map, the Morse function $g$. We then study $\mathcal{F}$ by looking at the intersection of its leaves with the level sets of $g$, and the way how these intersections change as the sphere gets smaller.

arXiv commentAccepted for publication by the Journal of Topology