The principal-block dimension conjecture for -spetses

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Let ℓ>0\ell>0 be prime. Let G=(Wφ−1,L)\mathbb{G}=(W\varphi^{-1},L) be a simply connected Zℓ\mathbb{Z}_\ell-spets for which ℓ\ell is very good, let qq be a power of a prime different from ℓ\ell, and let B0B_0 be the principal ℓ\ell-block of G(q)\mathbb{G}(q) with defect group SS. Define

dim⁡(B0):=∑γ∈Irr⁡(B0)γ(1)2∈Z[x].\dim(B_0):=\sum_{\gamma\in\operatorname{Irr}(B_0)}\gamma(1)^2\in\mathbb{Z}[x].

Principal-block dimension conjecture.

(dim⁡(B0)∣x=q)ℓ=∣S∣\left(\dim(B_0)|_{x=q}\right)_\ell=|S|

and

(dim⁡(B0)∣x=q)ℓ′≡∣Wφ−1ζ−1∣ℓ′(modℓ),\left(\dim(B_0)|_{x=q}\right)_{\ell'}\equiv |W_{\varphi^{-1}\zeta^{-1}}|_{\ell'}\pmod\ell,

where ζ∈Zℓ×\zeta\in\mathbb{Z}_\ell^\times satisfies q≡ζ(modℓ)q\equiv\zeta\pmod\ell, and Wφ−1ζ−1W_{\varphi^{-1}\zeta^{-1}} is the associated relative Weyl group. This combines the two stated dimension and global-local assertions; the paper proves it under additional hypotheses, but the general case is described as elusive.

References

Primary source

Radha Kessar, Gunter Malle and Jason Semeraro, “The principal block of a Z_-spets and Yokonuma type algebras”, arXiv:2106.14499 (2021).

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