Lusztig's character formula conjecture

Assume that pp is the characteristic, hh is the Coxeter number, WaffW_{\mathrm{aff}}^\varnothing is the specified subset of the affine Weyl group, ρ\rho is the half-sum of positive roots, \bullet denotes the affine dot action, Φ+\Phi_+^\vee is the set of positive coroots, cy,wc_{y,w}^\varnothing are the character coefficients, \ell is the length function, ww_\circ is the longest element, and hx,z(1)h_{x,z}(1) denotes the relevant Kazhdan–Lusztig polynomial evaluated at 11.

Lusztig's character formula conjecture. If php \geq h and wWaffw \in W_{\mathrm{aff}}^\varnothing satisfies

w0+ρ,αp(ph+2)\langle w \bullet 0+\rho,\alpha^\vee\rangle\leq p(p-h+2)

for every αΦ+\alpha^\vee\in\Phi_+^\vee, then

cy,w=(1)(w)+(y)hwy,ww(1)c_{y,w}^\varnothing=(-1)^{\ell(w)+\ell(y)}h_{w_\circ y,w_\circ w}(1)

for every yWaffy\in W_{\mathrm{aff}}^\varnothing.

The conjecture is presented as the character-formula problem for simple modules. Its status is not established by the supplied text.

Sources & referencesView supporting material

Primary source

Pramod N. Achar and Simon Riche, “Tilting modules for reductive algebraic groups: characters and support varieties”, arXiv:2511.05063 (2025).

Additional references

4 papers in this index state this conjecture (2024–2025). The statement above is taken from the most recent of them; the others are arXiv:2512.07836, arXiv:2502.09605, arXiv:2403.03734.

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