The Universal Askey–Wilson Algebra and DAHA of Type $(C_1^{\vee},C_1)$

Paul Terwilliger

Symmetry, integrability and geometry: methods and applications, Tome 9 (2013)

Résumé

Let $\mathbb F$ denote a field, and fix a nonzero $q\in\mathbb F$ such that $q^4\not=1$. The universal Askey–Wilson algebra $\Delta_q$ is the associative $\mathbb F$-algebra defined by generators and relations in the following way. The generators are $A$, $B$, $C$. The relations assert that each of \begin{gather*} A+\frac{qBC-q^{-1}CB}{q^2-q^{-2}}, \qquad B+\frac{qCA-q^{-1}AC}{q^2-q^{-2}}, \qquad C+\frac{qAB-q^{-1}BA}{q^2-q^{-2}} \end{gather*} is central in $\Delta_q$. The universal DAHA $\hat H_q$ of type $(C_1^\vee,C_1)$ is the associative $\mathbb F$-algebra defined by generators $\lbrace t^{\pm1}_i\rbrace_{i=0}^3$ and relations (i) $t_i t^{-1}_i=t^{-1}_i t_i=1$; (ii) $t_i+t^{-1}_i$ is central; (iii) $t_0t_1t_2t_3=q^{-1}$. We display an injection of $\mathbb F$-algebras $\psi:\Delta_q\to\hat H_q$ that sends \begin{gather*} A\mapsto t_1t_0+(t_1t_0)^{-1}, \qquad B\mapsto t_3t_0+(t_3t_0)^{-1}, \qquad C\mapsto t_2t_0+(t_2t_0)^{-1}. \end{gather*} For the map $\psi$ we compute the image of the three central elements mentioned above. The algebra $\Delta_q$ has another central element of interest, called the Casimir element $\Omega$. We compute the image of $\Omega$ under $\psi$. We describe how the Artin braid group $B_3$ acts on $\Delta_q$ and $\hat H_q$ as a group of automorphisms. We show that $\psi$ commutes with these $B_3$ actions. Some related results are obtained.

Détail

Keywords: Askey–Wilson polynomials; Askey–Wilson relations; rank one DAHA.

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