English

Free cyclic actions on surfaces and the Borsuk-Ulam theorem

Geometric Topology 2022-04-06 v1 Group Theory

Abstract

Let MM and NN be topological spaces, let GG be a group, and let τ ⁣:G×MM\tau \colon\thinspace G \times M \to M be a proper free action of GG. In this paper, we define a Borsuk-Ulam-type property for homotopy classes of maps from MM to NN with respect to the pair (G,τ)(G,\tau) that generalises the classical antipodal Borsuk-Ulam theorem of maps from the nn-sphere Sn\mathbb{S}^n to Rn\mathbb{R}^n. In the cases where MM is a finite pathwise-connected CW-complex, GG is a finite, non-trivial Abelian group, τ\tau is a proper free cellular action, and NN is either R2\mathbb{R}^2 or a compact surface without boundary different of S2\mathbb{S}^2 and RP2\mathbb{RP}^2, we give an algebraic criterion involving braid groups to decide whether a free homotopy class β[M,N]\beta \in [M,N] has the Borsuk-Ulam property. As an application of this criterion, we consider the case where MM is a compact surface without boundary equipped with a free action τ\tau of the finite cyclic group Zn\mathbb{Z}_n. In terms of the orientability of the orbit space MτM_\tau of MM by the action τ\tau, the value of nn modulo 44 and a certain algebraic condition involving the first homology group of MτM_\tau, we are able to determine if the single homotopy class of maps from MM to R2\mathbb{R}^2 possesses the Borsuk-Ulam property with respect to (Zn,τ)(\mathbb{Z}_n,\tau). Finally, we give some examples of surfaces on which the symmetric group acts, and for these cases, we obtain some partial results regarding the Borsuk-Ulam property for maps whose target is R2\mathbb{R}^2.

Keywords

Cite

@article{arxiv.2204.02065,
  title  = {Free cyclic actions on surfaces and the Borsuk-Ulam theorem},
  author = {Daciberg Lima Gonçalves and John Guaschi and Vinicius Casteluber Laass},
  journal= {arXiv preprint arXiv:2204.02065},
  year   = {2022}
}

Comments

18 pages, 2 figures