English

Relatively hyperbolic groups with free abelian second cohomology

Group Theory 2020-04-21 v2

Abstract

Suppose GG is a 1-ended finitely presented group that is hyperbolic relative to P\mathcal P a finite collection of 1-ended finitely presented proper subgroups of GG. Our main theorem states that if the boundary (G,P)\partial (G,{\mathcal P}) is locally connected and the second cohomology group H2(P,ZP)H^2(P,\mathbb ZP) is free abelian for each PPP\in \mathcal P, then H2(G,ZG)H^2(G,\mathbb ZG) is free abelian. When GG is 1-ended it is conjectured that (G,P)\partial (G,\mathcal P) is always locally connected. Under mild conditions on GG and the members of P\mathcal P the 1-ended and local connectivity hypotheses can be eliminated and the same conclusion is obtained. When GG and each member of P\mathcal P is 1-ended and (G,P)\partial (G,\mathcal P) is locally connected, we prove that the "Cusped Space" for this pair has semistable fundamental group at \infty. This provides a starting point in our proof of the main theorem.

Keywords

Cite

@article{arxiv.1812.08893,
  title  = {Relatively hyperbolic groups with free abelian second cohomology},
  author = {Michael Mihalik and Eric Swenson},
  journal= {arXiv preprint arXiv:1812.08893},
  year   = {2020}
}

Comments

31 pages, 8 figures

R2 v1 2026-06-23T06:52:04.647Z