Elementary-divisor conjecture for critical groups of induced representations

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Let AA be an abelian group of order rr, let S\mathfrak{S} denote the tower of symmetric groups, and consider the differential tower of groups A≀SA\wr\mathfrak{S}. For k≤nk\leq n, let V(UkDk)nV(U^kD^k)_n be the induced representation corresponding to UkDkU^kD^k, and let pjp_j denote the rank sizes. Write eie_i for the non-unit elementary divisors of the critical group K(V(DkUk)n−k)K(V(D^kU^k)_{n-k}). Elementary-divisor conjecture. The critical group

K(V(UkDk)n)=K(Ind⁡A≀Sn−kA≀Sn1)K(V(U^kD^k)_n)=K\left(\operatorname{Ind}_{A\wr\mathfrak{S}_{n-k}}^{A\wr\mathfrak{S}_n}\mathbb{1}\right)

is given, as a list of elementary divisors, by

(1pn−k,(rkn!(n−k)!)pn−2pn−k+pn−2k,rkn!(n−k)!ei),\left(1^{p_{n-k}},\left(r^{k}\frac{n!}{(n-k)!}\right)^{p_n-2p_{n-k}+p_{n-2k}},r^{k}\frac{n!}{(n-k)!}e_i\right),

where exponents involving rank sizes denote multiplicities. This predicts the precise elementary-divisor structure of these critical groups in the wreath-product differential tower.

References

Primary source

Ayush Agarwal and Christian Gaetz, “Differential posets and restriction in critical groups”, arXiv:1710.08253 (2020).

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