The Stable Homology of Congruence Subgroups

30 Jan 2015  ·  Calegari Frank ·

In a previous paper, the author (together with Matthew Emerton) proved that the completed cohomology groups of SL_N(Z) are stable in fixed degree as N goes to infinity (Z may be replaced by the ring O_F of integers of any number field). In this paper, we relate these completed cohomology groups to K-theory and Galois cohomology... Various consequences include showing that Borel's stable classes become infinitely p-divisible up the p-congruence tower if and only if a certain p-adic zeta value is non-zero. We use our results to compute H_2(Gamma_N(p),F_p) (for sufficiently large N) where Gamma_N(p) is the full level-p congruence subgroup of SL_N(Z). read more

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Algebraic Topology Geometric Topology Number Theory