Let us consider the quantum group $U_q(\mathfrak{sl}_2)$ (as defined in Kassel's book on quantum groups), for $q$ being a root of unity of order $d$ (i.e., $d$ is the smallest positive integer for which $q^d=1$). If $n$ is the dimension of an irreducible, finite-dimensional representation of $U_q(\mathfrak{sl}_2)$ (over a complex vector space), then it is known that $n$ is bounded above by $$ e=\begin{cases} d, & \text{$d$ odd} \\ d/2, & \text{$d$ even.} \end{cases} $$$$ e=\begin{cases} d, & \text{$d$: odd} \\ d/2, & \text{$d$: even.} \end{cases} $$ As far as I know, there are indecomposable, non-simple modules of dimension higher than $e$. I have made some small search on the structure of such modules, but I have not found anything substantial apart from Chari and Premet - Indecomposable restricted representations of quantum $sl_2$ (pdf abstract MSN), which however refers to the restricted case. So my questions are:
- Is there some reference on the structure of indecomposable, non-simple modules of quantum groups at roots of unity?
- Are there infinite dimensional, indecomposable, non-irreducibles?
- How can the limits of such representations (either fin or inf dimensional) at $q\to 1$, be computed?
I would be interested either on references or on some short—if possible-—description of such modules, mainly for the case of $U_q(\mathfrak{sl}_2)$ and more generally for $U_q(\mathfrak{g})$, where $\mathfrak{g}$ is a finite-dimensional, simple, complex Lie algebra.
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