A quantum shuffle approach to admissible quantum affine (super-)algebra of types $A_1^{(1)}$ and $C(2)^{(2)}$ and their equitable presentations
Xin Zhong, Naihong Hu
TL;DR
The paper develops a unified, Catalan-word–driven framework for the positive parts of the admissible quantum affine algebra of type $A_1^{(1)}$ and the quantum affine superalgebra $C(2)^{(2)}$, embedding them into a $q$-shuffle (super)algebra to realize Damiani and Beck PBW bases in closed form. By introducing Catalan elements and a Rosso-type embedding, the authors translate root-vector constructions into explicit shuffle-algebra expressions, and establish an equitable presentation for the admissible affine algebra along with a minimal bosonization for the superalgebra. They also connect two prominent PBW bases via generating-function techniques and prove new Catalan-relations that govern the interaction of the Catalan elements under the $q$-shuffle product, exploiting a recursive Catalan definition tailored to the super case. The results yield a practical, computable bridge between PBW bases, shuffle algebras, and equitable/bosonized presentations, with potential extensions to $i$-quantum groups and Drinfeld realizations.
Abstract
In this study, we focus on the positive part $U_q^{+}$ of the admissible quantum affine algebra $\mathcal{U}_q(\widehat{\mathfrak{s l}_2})$, newly defined in \cite{HZ}, and the quantum affine superalgebra $U_q(C(2)^{(2)})$. Both of these algebras have presentations involving two generators, $e_α$ and $e_{δ-α}$, which satisfy the cubic $q$-Serre relations. According to the works of Hu-Zhuang and Khoroshkin-Lukierski-Tolstoy, there exist the Damiani and the Beck $PBW$ bases for these two (super)algebras. In this paper, we employ the $q$-shuffle (super)algebra and Catalan words to present these two bases in a closed-form expression. Ultimately, the equitable presentations of $\mathcal{U}_q(\widehat{\mathfrak{sl}_2})$ and the bosonization of $U_q(C(2)^{(2)})$ are presented.
