Global monomial-set conjecture for simple Lie algebras

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Let d:Δ+→N\boldsymbol{d}:\Delta_+\rightarrow\mathbb{N} be a degree function for U(n−)U(\mathfrak n^-), and let Sgm⁡\mathcal{S}_{\operatorname*{gm}} be the set of degree functions such that, for every dominant integral weight λ\lambda, the defining ideal Id(λ)I^{\boldsymbol{d}}(\lambda) of gr⁡dV(λ)\operatorname{gr}^{\boldsymbol{d}}V(\lambda) is monomial. For a reduced expression w‾0\underline{w}_0 of the longest Weyl-group element, let Dw‾0q\mathcal{D}_{\underline{w}_0}^q denote the corresponding quantum degree cone. Global monomial-set conjecture.

  1. Sgm⁡≠∅\mathcal{S}_{\operatorname*{gm}}\neq\emptyset for any simple finite-dimensional Lie algebra g\mathfrak g.
  2. For any simply-laced simple Lie algebra, there exists w‾0\underline{w}_0 such that Sgm⁡∩Dw‾0q\mathcal{S}_{\operatorname*{gm}}\cap\mathcal{D}_{\underline{w}_0}^q is non-empty.

The known cases include types AnA_n, CnC_n, B3B_3, D4D_4 and G2G_2; the conjecture seeks degree functions producing monomial ideals beyond these cases, with the second assertion imposing compatibility with a quantum degree cone.

References

Primary source

Teodor Backhaus, Xin Fang and Ghislain Fourier, “Degree cones and monomial bases of Lie algebras and quantum groups”, arXiv:1605.00417 (2016).

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