The product formula conjecture for bounds of bounded affine Hecke algebra representations

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Let Φ\Phi be the root system, let (πJ,v,MJ,v,BJ,v)(\pi_{J,\mathsf{v}},M_{J,\mathsf{v}},\mathsf{B}_{J,\mathsf{v}}) be a bounded representation, and let aJ,v\mathbf{a}_{J,\mathsf{v}} denote its bound. For α∈Φ\alpha\in\Phi, define qα∈Z[q,q−1]\mathsf{q}_{\alpha}\in\mathbb{Z}[\mathsf{q},\mathsf{q}^{-1}] by

qα=qL(si)if Φ is reduced and α∈W0αi,\mathsf{q}_{\alpha}=\mathsf{q}^{L(s_i)}\quad\text{if $\Phi$ is reduced and $\alpha\in W_0\alpha_i$},

and, if Φ\Phi is not reduced,

qα={qL(si)if α∈W0αi with i≠n,qL(sn)−L(s0)if α∈W0αn,qL(s0)if α is long.\mathsf{q}_{\alpha}=\begin{cases} \mathsf{q}^{L(s_i)}&\text{if $\alpha\in W_0\alpha_i$ with $i\neq n$},\\ \mathsf{q}^{L(s_n)-L(s_0)}&\text{if $\alpha\in W_0\alpha_n$},\\ \mathsf{q}^{L(s_0)}&\text{if $\alpha$ is long.} \end{cases}

Product formula conjecture. If the representation is bounded, then

aJ,v=L(w0)−12deg⁡∏α∈Φ′1−qα/2−1vα∨1−qα/2−1qα−2vα∨,\mathbf{a}_{J,\mathsf{v}}=L(\mathsf{w}_0)-\frac{1}{2}\deg\prod_{\alpha\in\Phi}'\frac{1-\mathsf{q}_{\alpha/2}^{-1}\mathsf{v}^{\alpha^{\vee}}}{1-\mathsf{q}_{\alpha/2}^{-1}\mathsf{q}_{\alpha}^{-2}\mathsf{v}^{\alpha^{\vee}}},

where ∏′\prod' means that factors in the numerator or denominator that are 00 are omitted. This is presented as a stronger conjecture than the upper-bound conjecture and is intended to give the precise value of the bound; its status is open in the supplied text.

References

Primary source

Jérémie Guilhot, Eloise Little and James Parkinson, “On J-folded alcove paths and combinatorial representations of affine Hecke algebras”, arXiv:2212.10781 (2024).

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