Infinitesimal and tangential 16-th Hilbert problem on zero-cycles

Abstract

In this paper, given two polynomials $f$ and $g$ of one variable and a $0$-cycle $C$ of $f$, we consider the deformation $f+\hat{I}\mu g$. We define two functions: the displacement function $\hat{I}”(t,\hat{I}\mu )$ and its first order approximation: the abelian integral $M_1(t)$. The infinitesimal and tangential 16-th Hilbert problem for zero-cycles are problems of counting isolated regular zeros of $\hat{I}”(t,\hat{I}\mu )$, for $\hat{I}\mu$ small, or of $M_1(t)$, respectively. We show that the two problems are not equivalent and find optimal bounds, in function of the degrees of $f$ and $g$, for the infinitesimal and tangential 16-th Hilbert problem on zero-cycles. These two problems are the zero-dimensional analogue of the classical infinitesimal and tangential 16-th Hilbert problems for vector fields in the plane.

28 pages