有理函数的Berkovich分支轨迹的拓扑与几何
Topology and Geometry of the Berkovich Ramification Locus for Rational Functions
摘要：
给定紧致Riemann曲面之间的一个非常数全纯映射f：X-> Y，我们首先要构造的对象之一是它的分歧因子R_f，它描述了f不为局部内射的轨迹。因子R_f是X上的点的有限形式线性组合，它受Hurwitz公式的组合约束。现在设k是一个代数闭域，它关于一个非平凡的非阿基米得绝对值是完备的。例如，k = C_p。这里黎曼曲面的作用是由一条射影的伯科维奇解析曲线来扮演的。由于这些曲线有许多点不是在k上代数的，因此它们之间的映射出现了一些新的（非代数的）分歧行为。例如，分歧轨迹不再是除数，而是一个封闭的解析子空间。本文对自映射f：P^1-> P^1的分歧轨迹进行了详细的研究。这个最简单的第一种情况的好处是可以通过具体的（通常是组合的）技术来实现。
英文摘要：
Given a nonconstant holomorphic map f: X -> Y between compact Riemann surfaces, one of the first objects we learn to construct is its ramification divisor R_f, which describes the locus at which f fails to be locally injective. The divisor R_f is a finite formal linear combination of points of X that is combinatorially constrained by the Hurwitz formula. Now let k be an algebraically closed field that is complete with respect to a nontrivial non-Archimedean absolute value. For example, k = C_p. Here the role of a Riemann surface is played by a projective Berkovich analytic curve. As these curves have many points that are not algebraic over k, some new (non-algebraic) ramification behavior appears for maps between them. For example, the ramification locus is no longer a divisor, but rather a closed analytic subspace. This article initiates a detailed study of the ramification locus for self-maps f: P^1 -> P^1. This simplest first case has the benefit of being approachable by concrete (and often combinatorial) techniques.
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