On Refined Filtration By Supports for Rational Cherednik Categories O

For a complex reflection group $W$ with reflection representation $\mathfrak{h}$, we define and study a natural filtration by Serre subcategories of the category $\mathcal{O}_c(W, \mathfrak{h})$ of representations of the rational Cherednik algebra $H_c(W, \mathfrak{h})$. This filtration refines the filtration by supports and is analogous to the Harish-Chandra series appearing in the representation theory of finite groups of Lie type. Using the monodromy of the Bezrukavnikov-Etingof parabolic restriction functors, we show that the subquotients of this filtration are equivalent to categories of finite-dimensional representations over generalized Hecke algebras. When $W$ is a finite Coxeter group, we give a method for producing explicit presentations of these generalized Hecke algebras in terms of finite-type Iwahori-Hecke algebras. This yields a method for counting the number of irreducible objects in $\mathcal{O}_c(W, \mathfrak{h})$ of given support. We apply these techniques to count the number of irreducible representations in $\mathcal{O}_c(W, \mathfrak{h})$ of given support for all exceptional Coxeter groups $W$ and all parameters $c$, including the unequal parameter case. This completes the classification of the finite-dimensional irreducible representations of $\mathcal{O}_c(W, \mathfrak{h})$ for exceptional Coxeter groups $W$ in many new cases.