English

Quasisections of circle bundles and Euler class

Geometric Topology 2025-04-10 v2

Abstract

Let EπB E \xrightarrow[\text{}]{\pi} B be an oriented circle bundle over an oriented closed surface BB. A quasisection is a smooth surface Q{Q} (either closed or bordered) mapped by a generic smooth mapping qq to EE such that πq(Q)=B\pi\circ q({Q})=B. In the paper we derive a local formula for the Euler number, that is, we show that Euler number (Euler class) of the bundle equals the sum of weights of (some of) singularities of a quasisection.We also prove the uniqueness of such a formula. The local formula is a close relative of M. Kazarian's formula which relates the Euler number and Morse bifurcations of a generic function defined on the total space EE.

Keywords

Cite

@article{arxiv.2410.22453,
  title  = {Quasisections of circle bundles and Euler class},
  author = {Gaiane Panina and Timur Shamazov and Maksim Turevskii},
  journal= {arXiv preprint arXiv:2410.22453},
  year   = {2025}
}
R2 v1 2026-06-28T19:40:17.484Z