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arXiv 1707.03366math.RTmath.CO
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Kac-Moody旗簇中的行走代数、特殊子表达式和点计数

Walk algebras, distinguished subexpressions, and point counting in Kac-Moody flag varieties

Dinakar Muthiah, Daniel Orr

摘要:

研究了Kac-Moody根系的行走代数和Hecke代数。每一个选择的方向的一组实根产生一个相应的“定向”的基础,这些代数。我们发现,当研究定向基之间的转移阵时,自然会出现区分子表达式的概念。然后,我们将这些概念的几何形状的卡茨-穆迪旗品种和Bott-Samelson品种。特别是,我们表明,在有限域上的点的数量在这些品种的某些交叉给出的基础系数之间的变化定向基地的Hecke代数。利用这些结果,我们给流线型推导的Deodhar的公式$R$ -多项式和点计数公式的专业化的非对称麦克唐纳多项式$E_λ(\mathsf{q},t)$在$\mathsf{q}=0,\infty$。

英文摘要:

We study walk algebras and Hecke algebras for Kac-Moody root systems. Each choice of orientation for the set of real roots gives rise to a corresponding "oriented" basis for each of these algebras. We show that the notion of distinguished subexpression naturally arises when studying the transition matrix between oriented bases. We then relate these notions to the geometry of Kac-Moody flag varieties and Bott-Samelson varieties. In particular, we show that the number of points over a finite field in certain intersections of these varieties is given by change of basis coefficients between oriented bases of the Hecke algebra. Using these results we give streamlined derivations of Deodhar's formula for $R$-polynomials and point-counting formulas for specializations of nonsymmetric Macdonald polynomials $E_λ(\mathsf{q},t)$ at $\mathsf{q}=0,\infty$.

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