Braden–MacPherson stalk-rank conjecture

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Let RR be a reduced, irreducible, finite root system, let W^\widehat{\mathcal W} be its affine Weyl group, and let kk be a field. Form the associated moment graph G^k\widehat{\mathcal G}_k over Wk=X^∨⊗ZkW_k=\widehat X^\vee\otimes_{\mathbb Z}k. For w∈W^w\in\widehat{\mathcal W}, let Bk,w\mathcal B_{k,w} be the space of global sections of the Braden--MacPherson sheaf on the truncated moment graph, and let Bk,wx\mathcal B_{k,w}^x be its stalk at xx. Define the graded rank by

rk⁡‾ Bk,wx=∑iv2li\underline{\operatorname{rk}}\,\mathcal B_{k,w}^x=\sum_i v^{2l_i}

when Bk,wx≅⨁iS{li}\mathcal B_{k,w}^x\cong\bigoplus_i S\{l_i\}. Let Px,wP_{x,w} be the Kazhdan--Lusztig polynomial. Braden–MacPherson stalk-rank conjecture. If kk and ww are such that G^k,w\widehat{\mathcal G}_{k,w} is a GKM-graph, then

rk⁡‾ Bk,wx=Px,w(v−2)\underline{\operatorname{rk}}\,\mathcal B_{k,w}^x=P_{x,w}(v^{-2})

for all x≤wx\leq w. This conjecture is the moment-graph multiplicity conjecture underlying the paper's approach to Lusztig's conjecture; the supplied text does not state that it has been resolved.

References

Primary source

Peter Fiebig, “The multiplicity one case of Lusztig's conjecture”, arXiv:math/0607501 (2009).

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