All-level torsion growth conjecture for arithmetic groups

Let Γ\Gamma be an arithmetic group, let Γk\Gamma_k range over congruence subgroups of Γ\Gamma of increasing level, and let δ\delta denote the deficiency of the associated real semisimple group. Let ii be the degree at the top of the cuspidal range, and let L\mathscr{L} be the coefficient lattice. All-level torsion growth conjecture. When δ=1\delta=1, the limit

limklogHi(Γk;L)tors[Γ:Γk]\lim_{k\rightarrow\infty}\frac{\log\lvert H^i(\Gamma_k;\mathscr{L})_{\operatorname{tors}}\rvert}{[\Gamma:\Gamma_k]}

should equal the Bergeron–Venkatesh limit for any set of congruence subgroups of increasing level. In particular,

lim infΓklogHi(Γk;L)tors[Γ:Γk]\liminf_{\Gamma_k}\frac{\log\lvert H^i(\Gamma_k;\mathscr{L})_{\operatorname{tors}}\rvert}{[\Gamma:\Gamma_k]}

taken over all congruence subgroups should equal that limit. This strengthens the prime-level version by allowing arbitrary increasing levels; the paper offers computational evidence, while the assertion remains unproved.

Sources & referencesView supporting material

Primary source

Avner Ash, Paul E. Gunnells, Mark McConnell and Dan Yasaki, “On the growth of torsion in the cohomology of arithmetic groups”, arXiv:1608.05858 (2016).

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