Barbasch-Sahi algebras and Dirac cohomology

TL;DR

This paper introduces Barbasch-Sahi algebras, a new class of Hopf-Hecke algebras, and develops Dirac cohomology theory for them, generalizing key concepts from Lie groups and related algebraic structures.

Contribution

It defines Barbasch-Sahi algebras, constructs Dirac cohomology for their modules, and proves a Vogan-type conjecture linking central characters and Dirac cohomology.

Findings

Established the existence of a pin cover for certain cocommutative Hopf algebras.

Defined Dirac operator and cohomology for Hopf-Hecke algebra modules.

Proved a generalized Vogan's conjecture for Barbasch-Sahi algebras.

Abstract

We define a class of algebras which are distinguished by a PBW property and an orthogonality condition, and which we call Hopf-Hecke algebras, since they generalize the Drinfeld Hecke algebras defined by Drinfeld. In the course of studying the orthogonality condition and in analogy to the orthogonal group we show the existence of a pin cover for cocommutative Hopf algebras over $\mathbb{C}$ with an orthogonal module or, more generally, pointed cocommutative Hopf algebras over a field of characteristic $0$ with an orthogonal module. Following the suggestion of Dan Barbasch and Siddhartha Sahi, we define a Dirac operator and Dirac cohomology for modules of Hopf-Hecke algebras, generalizing those concepts for connected semisimple Lie groups, graded affine Hecke algebras and symplectic reflection algebras. Using the pin cover, we prove a general theorem for a class of Hopf-Hecke algebras which we call Barbasch-Sahi algebras, which relates the central character of an irreducible module with non-vanishing Dirac cohomology to the central characters occurring in its Dirac cohomology, generalizing a result called "Vogan's conjecture" for connected semisimple Lie groups, analogous results for graded affine Hecke algebras and for symplectic reflection algebras and Drinfeld Hecke algebras.