Trinh–Xue's conjecture on intersections of Hecke-algebra blocks

Let GG be a finite reductive group, let e,d1e,d\ge1 be such that Φe\Phi_e and Φd\Phi_d divide the order polynomial of GG, and let (L,λ)({\mathbf L},\lambda) and (M,μ)({\mathbf M},\mu) be, respectively, an ee-cuspidal and a dd-cuspidal pair. For a complete HC-parametrisation Ψ={ΨL,λ}\Psi=\{\Psi_{{\mathbf L},\lambda}\}, the corresponding Harish-Chandra series are the images of the irreducible characters of the associated cyclotomic Hecke algebras under the maps ΨL,λ\Psi_{{\mathbf L},\lambda}. Let ζe\zeta_e and ζd\zeta_d be primitive eeth and ddth roots of unity, respectively, and let blocks mean the block partitions of the specialised Hecke algebras.

Trinh–Xue's conjecture. There exists a choice of complete HC-parametrisation Ψ={ΨL,λ}\Psi=\{\Psi_{{\mathbf L},\lambda}\} such that, for every such pair (L,λ)({\mathbf L},\lambda) and (M,μ)({\mathbf M},\mu), the intersection

ΨL,λ(Irr(H(W(L,λ),x)))ΨM,μ(Irr(H(W(M,μ),x)))\Psi_{{\mathbf L},\lambda}(\operatorname{Irr}({\mathcal H}(W({\mathbf L},\lambda),x)))\cap\Psi_{{\mathbf M},\mu}(\operatorname{Irr}({\mathcal H}(W({\mathbf M},\mu),x)))

admits a partition Bi\bigsqcup B_i such that, for every ii, ΨL,λ1(Bi)\Psi_{{\mathbf L},\lambda}^{-1}(B_i) is a block of H(W(L,λ),ζd){\mathcal H}(W({\mathbf L},\lambda),\zeta_d) and ΨM,μ1(Bi)\Psi_{{\mathbf M},\mu}^{-1}(B_i) is a block of H(W(M,μ),ζe){\mathcal H}(W({\mathbf M},\mu),\zeta_e). In particular, this defines a bijection between the blocks of the two algebras appearing in this intersection.

The conjecture seeks a common block partition for intersections of Harish-Chandra series associated with different cyclotomic parameters. The source notes that the partitions depend on the choice of complete HC-parametrisation and that no analogous relation is known there in general for e>1e>1.

Sources & referencesView supporting material

Primary source

Maria Chlouveraki and Gunter Malle, “Intersections of blocks of cyclotomic Hecke algebras”, arXiv:2506.12973 (2026).

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