The Littlewood–Richardson rule for Λ\Lambda-cominuscule elements

Let GG be a Kac–Moody group, let PP be a parabolic subgroup, and let X=G/PX=G/P. Let WW be the Weyl group, and let Λ\Lambda be the dominant weight associated with PP. Let cu,vwc_{u,v}^w be the Schubert structure constants and let tu,vwt_{u,v}^w be the jeu de taquin integer for u,vwu,v\leq w. For a Λ\Lambda-cominuscule element w=sα1sαlw=s_{\alpha_1}\cdots s_{\alpha_l}, define m(w)m(w) by

m(w):=i[1,l], αS(Λ),(α,α)>(αi,αi), i(α,1)(α,α)(αi,αi),m(w):=\prod_{\substack{i\in[1,l],\ \alpha\in S(\Lambda),\\(\alpha,\alpha)>(\alpha_i,\alpha_i),\ i\geq(\alpha,1)}}\frac{(\alpha,\alpha)}{(\alpha_i,\alpha_i)},

where S(Λ)={α:Λ,α>0}S(\Lambda)=\{\alpha:\langle\Lambda,\alpha^\vee\rangle>0\}, (,)(\cdot,\cdot) is a WW-invariant scalar product, and (α,1)(\alpha,1) is the minimal element of the heap colored by α\alpha. Set mu,vw=m(w)/(m(u)m(v))m_{u,v}^w=m(w)/(m(u)m(v)). The Λ\Lambda-cominuscule Littlewood–Richardson conjecture. For ww a Λ\Lambda-cominuscule element and uu and vv in WW smaller than ww, we have

cu,vw=mu,vwtu,vw.c_{u,v}^w=m_{u,v}^w t_{u,v}^w.

This extends the proposed jeu de taquin rule from Λ\Lambda-minuscule to Λ\Lambda-cominuscule elements by incorporating the root-length correction factor mu,vwm_{u,v}^w. The source provides no resolution status.

Sources & referencesView supporting material

Primary source

Pierre-Emmanuel Chaput and Nicolas Perrin, “Towards a Littlewood-Richardson rule for Kac-Moody homogeneous spaces”, arXiv:0902.0152 (2009).

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