The ultimate goal of this project is to obtain results analogous to the Vershik-Kerov limit shape, but for quantum groups at roots of unity, where the category of representations is non-semisimple. In other words, we want to study central limit theorems describing statistics of indecomposable components in tensor product decomposition of representations of Uq(sln) with respect to Plancherel and character measures, when tensor power goes to infinity, the highest weight of the indecomposable component goes to infinity, and, ideally, rank of algebra also goes to infinity, while root of unity remains fixed or grows proportionally to the rank.
We initiate this project by studying Uq(sl2) with divided powers and the small quantum sl2. We represent relations in the Grothendieck ring of the category of tilting modules of Uq(sl2) with divided powers as a random walk in a lattice path model, where weighted numbers of descending paths satisfy the same recurrsion relations as multiplicities of indecomposable components in tensor product decomposition. We study limiting distributions of these random walks: most probable trajectory and fluctuations in its vicinity. We do so in multiple regimes: in the bulk, for the intermediate scaling, for the critical drift. We restrict Uq(sl2) with divided powers to uq(sl2) to obtain formulas for multiplicities, which we then use to study the limit shape of the Plancherel measure.
Mentioned results for the case of classical Lie algebras enjoy certain universality properties, where limiting distributions don't depend on tensor power of which particular representation is being considered. Since for the non-semisimple case limiting distribution is manifested by a tensor product of two distributions, one of which is discrete, it is important to study whether this universality is still present. In [4] we study the same statistics for tensor powers of arbitrary tilting module T(k).
In [5] we initiate the study of Uq(sl3), which heavily relies on 'inverse' Kazhdan-Lusztig polynomials and their asymptotic behavior along rays in the Weyl chamber.