A generalization of the Gauss-Bonnet and Hopf-Poincar\'e theorems. Part II

Abstract

This paper is a continuation of the paper F. A. Arias and M. Malakhaltsev "A generalization of the Gauss-Bonnet and Hopf-Poincar\'e theorems", ArXiv:1510.01395 [MathDG] 5 Oct 2015. Let $\pi : E \to M$ be a locally trivial fiber bundle over a two-dimensional manifold $M$, and $\Sigma \subset M$ be a discrete subset. A subset $Q \subset E$ is called an $n$-sheeted branched section of the bundle $\pi$ if $Q' = \pi^{-1}(M \setminus \Sigma) \cap Q$ is a $n$-sheeted covering of $M \setminus \Sigma$. The set $\Sigma$ is called the singularity set of the branched section $Q$. We define the index of a singularity point of a branched section, and give examples of its calculation, in particular for branched sections of the projective tangent bundle of $M$ determined by binary differential equations. Also we define a resolution of singularities of a branched section, and prove an analog of Hopf-Poincar\'e-Gauss-Bonnet theorem for the branched sections admitting a resolution.