Multiplicity Estimates: a Morse-theoretic approach

TL;DR

This paper refines existing methods for estimating the multiplicity of polynomial zeros along trajectories of polynomial vector fields, providing geometric and topological insights and extending classical estimates using Newton polytopes.

Contribution

It improves Gabrielov's multiplicity estimate, offers a geometric topological description, and generalizes classical bounds with Newton polytope techniques.

Findings

Refined Gabrielov's estimate for polynomial zero multiplicity.

Provided a geometric description using polar varieties.

Extended estimates using Newton polytopes.

Abstract

The problem of estimating the multiplicity of the zero of a polynomial when restricted to the trajectory of a non-singular polynomial vector field, at one or several points, has been considered by authors in several different fields. The two best (incomparable) estimates are due to Gabrielov and Nesterenko. In this paper we present a refinement of Gabrielov's method which simultaneously improves these two estimates. Moreover, we give a geometric description of the multiplicity function in terms certain naturally associated polar varieties, giving a topological explanation for an asymptotic phenomenon that was previously obtained by elimination theoretic methods in the works of Brownawell, Masser and Nesterenko. We also give estimates in terms of Newton polytopes, strongly generalizing the classical estimates.