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OP-8522Status unassessedGeometry and topology

Approximation of L2L_2-torsion. · Question 1.1

L2L^2 invariants and their relatives for finitely generated groups · Historical workshop question

Editorial mapping of AIMPL source category: Geometric group theory. http://aimpl.org/l2invariantsgroups/ Not an author-supplied MSC code.

Historical list · status unassessedAs of 2026-09-08Source & evidence ↓

Problem statement

Do we have

ρ(2)(M~)=(−1)klim⁡log⁡(∣tors(Hk(Mn))∣)∣Γ:Γn∣?\rho^{(2)}(\tilde{M})=(-1)^k\lim \frac{\log(|tors (H_k(M_n))|)}{|\Gamma:\Gamma_n|}?

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Background

Workshop introduction

This problem list concerns the study of the asymptotic behavior of some natural invariants of finitely generated groups.

Question context

Let MM be a closed Riemannian manifold and let Γ=π1(M)>Γ1>Γ2>…\Gamma=\pi_1(M)>\Gamma_1>\Gamma_2>\ldots be a decreasing sequence of finite index normal subgroups of Γ\Gamma with ⋂Γn=1\bigcap\Gamma_n=1. Let M~\tilde{M} be the universal cover of MM and let Mn=M~/ΓnM_n=\tilde{M}/\Gamma_n.

In addition, suppose that MM is aspherical with dim⁡M=2k+1\dim M=2k+1 and βj(2)=0\beta_j^{(2)}=0 for every jj.

Progress & source assessment

Historical workshop record. Current open/solved status has not been independently reassessed.

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References
  1. [1]$L^2$ invariants and their relatives for finitely generated groups link

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