Virtual Homological Torsion of Closed Hyperbolic 3-manifolds

TL;DR

This paper demonstrates that every finite abelian group can be realized as a direct summand of the torsion part of the first homology group in some finite cover of any closed hyperbolic 3-manifold, using geometric and group-theoretic techniques.

Contribution

It introduces a method to realize arbitrary finite abelian groups as homological torsion in finite covers of closed hyperbolic 3-manifolds, leveraging almost totally geodesic surfaces and subgroup separability.

Findings

Any finite abelian group appears as a summand of torsion in some finite cover.

Construction of specific 2-complexes using geodesic surfaces.

Application of LERF and quasi-convex subgroup properties to 3-manifold groups.

Abstract

In this paper, we will use Kahn-Markovic's almost totally geodesic surfaces to construct certain $\pi_1$-injective 2-complexes in closed hyperbolic 3-manifolds. Such 2-complexes are locally almost totally geodesic except along a 1-dimensional subcomplex. Using Agol and Wise's result that fundamental groups of hyperbolic 3-manifolds are LERF and quasi-convex subgroups are virtual retract, we will show that closed hyperbolic 3-manifolds virtually contain any prescribed homological torsion: For any finite abelian group $A$, and any closed hyperbolic 3-manifold $M$, there exists a finite cover $N$ of $M$, such that $A$ is a direct summand of $Tor(H_1(N;\mathbb{Z}))$.