Dual Polar Graphs, a nil-DAHA of Rank One, and Non-Symmetric Dual q-Krawtchouk Polynomials

Abstract

Let $\Gamma$ be a dual polar graph with diameter $D⩾3$, having as vertices the maximal isotropic subspaces of a finite-dimensional vector space over the finite field ${\mathbb{F}}_q$ equipped with a non-degenerate form (alternating, quadratic, or Hermitian) with Witt index $D$. From a pair of a vertex $x$ of $\Gamma$ and a maximal clique $C$ containing $x$, we construct a $2D$-dimensional irreducible module for a nil-DAHA of type $(C_1^{\vee },C_1)$, and establish its connection to the generalized Terwilliger algebra with respect to $x$, $C$. Using this module, we then define the non-symmetric dual $q$-Krawtchouk polynomials and derive their recurrence and orthogonality relations from the combinatorial points of view. We note that our results do not depend essentially on the particular choice of the pair $x$, $C$, and that all the formulas are described in terms of $q$, $D$, and one other scalar which we assign to $\Gamma$ based on the type of the form.

arXiv commentan extended abstract of this work appeared in proceedings for FPSAC 2017

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Cited by in corpus (5)

• Dualities in the $q$-Askey scheme and degenerate DAHA
• Dual Polar Graphs, a nil-DAHA of Rank One, and Non-Symmetric Dual q-Krawtchouk Polynomials
• An imperceptible connection between the Clebsch--Gordan coefficients of $U_q({\mathfrak{sl}}_2)$ and the Terwilliger algebras of Grassmann graphs
• Grassmann graphs, degenerate DAHA, and non-symmetric dual $q$-Hahn polynomials
• Finite-dimensional irreducible modules of the universal Askey--Wilson algebra at roots of unity