Conjectural type-A standard homomorphisms with a generator times the longest element

Fix nn and i[2,n2]i\in[2,n-2]. Let TiT_i be the standard generator and let w0[1,n1]w_0^{[1,n-1]} be the longest element of the parabolic subgroup on [1,n1][1,n-1] in type AnA_n.

Type-A twelve-period homomorphism conjecture. Define

T^1TiTn,T^2Tw0[1,n1].\widehat{T}_1\mapsto T_iT_n,\qquad \widehat{T}_2\mapsto T_{w_0^{[1,n-1]}}.

Then these assignments define a standard homomorphism

Br+(I2(12/d))Brn+1+,\operatorname{Br}^+(I_2(12/d))\to\operatorname{Br}^+_{n+1},

where

d=1+δ2i,n+δ2i,n1+δ2i,n+1.d=1+\delta_{2i,n}+\delta_{2i,n-1}+\delta_{2i,n+1}.

This is listed as another conjectural family of non-disjoint standard homomorphisms; the paper states that the families in this section were verified for n15n\le15.

Sources & referencesView supporting material

Primary source

Arkady Berenstein, Jacob Greenstein and Jian-Rong Li, “Artin monoids, their homomorphisms and twins”, arXiv:2606.26776 (2026).

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