# Subspace arrangements and Cherednik algebras

## TL;DR

This paper explores the connection between subspace arrangements from reflection groups and Cherednik algebra invariants, revealing new insights into their algebraic and geometric properties, including radical ideals and bases related to Jack polynomials.

## Contribution

It establishes a link between Betti numbers and Kazhdan-Lusztig characters, and characterizes when polynomial representations of Cherednik algebras are radical ideals, with explicit bases and Cohen-Macaulay properties.

## Key findings

- Equivalence between equivariant Betti numbers and Kazhdan-Lusztig characters.
- Conditions for the radical of polynomial representations to be radical ideals.
- Explicit bases for the socle of cyclotomic Cherednik algebra representations.

## Abstract

The purpose of this article is to study the relationship between numerical invariants of certain subspace arrangements coming from reflection groups and numerical invariants arising in the representation theory of Cherednik algebras. For instance, we observe that knowledge of the equivariant graded Betti numbers (in the sense of commutative algebra) of any irreducible representation in category O is equivalent to knowledge of the Kazhdan-Lusztig character of the irreducible object (we use this observation in joint work with Fishel-Manosalva). We then explore the extent to which Cherednik algebra techniques may be applied to ideals of linear subspace arrangements: we determine when the radical of the polynomial representation of the Cherednik algebra is a radical ideal, and, for the cyclotomic rational Cherednik algebra, determine the socle of the polynomial representation and characterize when it is a radical ideal. The subspace arrangements that arise include various generalizations of the k-equals arrangment. In the case of the radical, we apply our results with Juteau together with an idea of Etingof-Gorsky-Losev to observe that the quotient by the radical is Cohen-Macaulay for positive choices of parameters. In the case of the socle (in cyclotomic type), we give an explicit vector space basis in terms of certain specializations of non-symmetric Jack polynomials, which in particular determines its minimal generators and Hilbert series and answers a question posed by Feigin and Shramov.