Schur functions in noncommuting variables

TL;DR

This paper introduces a new basis of Schur functions in noncommuting variables, extending classical properties and establishing connections to representation theory and noncommutative symmetric functions.

Contribution

It defines Schur functions in noncommuting variables using a noncommutative Jacobi-Trudi determinant, answering Rosas and Sagan's question and linking to Specht modules.

Findings

A basis of Schur functions in NCSym is constructed.

Noncommutative Schur functions satisfy a product rule analogous to classical ones.

The paper proves noncommutative Littlewood-Richardson and coproduct rules.

Abstract

In 2004 Rosas and Sagan asked whether there was a way to define a basis in the algebra of symmetric functions in noncommuting variables, NCSym, having properties analogous to the classical Schur functions. This was because they had constructed a partial such set that was not a basis. We answer their question by defining Schur functions in noncommuting variables using a noncommutative analogue of the Jacobi-Trudi determinant. Our Schur functions in NCSym map to classical Schur functions under commutation, and a subset of them indexed by set partitions forms a basis for NCSym. Amongst other properties, Schur functions in NCSym also satisfy a noncommutative analogue of the product rule for classical Schur functions in terms of skew Schur functions. We also show how Schur functions in NCSym are related to Specht modules, and naturally refine the Rosas-Sagan Schur functions. Moreover, by generalizing Rosas-Sagan Schur functions to skew Schur functions in the natural way, we prove noncommutative analogues of the Littlewood-Richardson rule and coproduct rule for them. Finally, we relate our functions to noncommutative symmetric functions by proving a subset of our functions are natural extensions of noncommutative ribbon Schur functions, and immaculate functions indexed by integer partitions.