Fixed point indices and periodic points of holomorphic mappings

Abstract

Let $\Delta ^{n}$ be the ball $|x|<1$ in the complex vector space $\mathbb{C}% ^{n}$, let $f:\Delta ^{n}\to \mathbb{C}^{n}$ be a holomorphic mapping and let $M$ be a positive integer. Assume that the origin $% 0=(0,..., 0)$ is an isolated fixed point of both $f$ and the $M$-th iteration $f^{M}$ of $f$. Then for each factor $m$ of $M,$ the origin is again an isolated fixed point of $f^{m}$ and the fixed point index $\mu_{f^{m}}(0)$ of $f^{m}$ at the origin is well defined, and so is the (local) Dold's index (see [\ref{Do}]) at the origin:% \begin{equation*} P_{M}(f,0)=\sum_{\tau \subset P(M)}(-1)^{#\tau}\mu_{f^{M:\tau}}(0), \end{equation*}% where $P(M)$ is the set of all primes dividing $M,$ the sum extends over all subsets $\tau $ of $P(M)$, $#\tau $is the cardinal number of $\tau $ and $% M:\tau =M(\prod_{p\in \tau}p)^{-1}$. $P_{M}(f,0)$ can be interpreted to be the number of periodic points of period $M$ of $f$ overlapped at the origin: any holomorphic mapping $% f_{1}:\Delta ^{n}\to \mathbb{C}^{n}$ sufficiently close to $f$ has exactly $P_{M}(f,0)$ distinct periodic points of period $M$ near the origin$%, $ provided that all the fixed points of $f_{1}^{M}$ near the origin are simple. Note that $f$ itself has no periodic point of period $M$ near the origin$.$ According to M. Shub and D. Sullivan's work [\ref{SS}], a necessary condition so that $P_{M}(f,0)\neq 0$ is that the linear part of $f$ at the origin has a periodic point of period $M.$ The goal of this paper is to prove that this condition is sufficient as well for holomorphic mappings.