Formulae of $\imath$-divided powers in ${\bf U}_q(\mathfrak{sl}_2)$, II

Abstract

The coideal subalgebra of the quantum $\mathfrak{sl}_2$ is a polynomial algebra in a generator $t$ which depends on a parameter $\kappa$. The existence of the $\imath$-canonical basis (also known as the $\imath$-divided powers) for the coideal subalgebra of the quantum $\mathfrak{sl}_2$ were established by Bao and Wang. We establish closed formulae for the $\imath$-divided powers as polynomials in $t$ and also in terms of Chevalley generators of the quantum $\mathfrak{sl}_2$ when the parameter $\kappa$ is an arbitrary $q$-integer. The formulae were known earlier when $\kappa=0,1$.