Conjecture A on graded character-shifted quantum Schubert cells

Let WW be the Weyl group, let wWw\in W, and let ϕ\phi be a character. Give Uq(g)U^-_q(\mathfrak{g}) the Z\mathbb{Z}-grading determined by deg(Eαi)=1\deg(E_{\alpha_i})=1, deg(Kαi)=0\deg(K_{\alpha_i})=0, and deg(Fαi)=1\deg(F_{\alpha_i})=-1. Let f:gr(U[w]ϕ)U0f:\operatorname{gr}(U^-[w]_{\phi})\to U^{\leq 0} be the canonical map sending an element to its summands of leading degree, and write D=im(f)D=\operatorname{im}(f). Let D0D^0 be the degree-zero part, set G(D0)=Kμ1μsupp(ϕ)G(D^0)=\\{K_{\mu}^{-1}\mid \mu\in\operatorname{supp}(\phi)\\}, and let G~\widetilde{G} denote its quotient group or localization. Define w=(βsupp(ϕ)sβ)ww'=\left(\prod_{\beta\in\operatorname{supp}(\phi)}s_{\beta}\right)w. Conjecture A. The algebra DD is a Z\mathbb{Z}-graded right coideal subalgebra of U0U^{\leq 0}, its degree-zero part is the semigroup algebra D0=k[G(D0)]D^0=\Bbbk[G(D^0)], and

k[G~(D0)]D=k[G~(D0)]U[w].\Bbbk[\widetilde{G}(D^0)]D=\Bbbk[\widetilde{G}(D^0)]U^-[w'].

Morally, this identifies the graded character shift with U[w]U^-[w'] up to localization and gives an explicit formula for the Weyl group element governing the graded algebra. The source presents this as an important structural conjecture for understanding the representation theory of right coideal subalgebras; its resolution status is not established in the supplied text.

Sources & referencesView supporting material

Primary source

Simon D. Lentner and Karolina Vocke, “On Borel subalgebras of quantum groups”, arXiv:1905.05867 (2024).

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