Generalised canonical basic sets for Ariki–Koike algebras

Abstract

Let H be a non-semi-simple Ariki–Koike algebra. According to [20] and [16], there is a generalisation of Lusztig's a-function which induces a natural combinatorial order (parametrised by a tuple m) on Specht modules. In some cases, Geck and Jacon have proved that this order makes the decomposition matrix of H unitriangular. The algebra H is then said to admit a “canonical basic set”. We fully classify which values of m yield a canonical basic set for H and which do not. When this is the case, we describe these sets in terms of “twisted Uglov” or “twisted Kleshchev” multipartitions.