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Weight Multiplicities and Young Tableaux Through Affine Crystals

About this Title

Jang Soo Kim, Kyu-Hwan Lee and Se-jin Oh

Publication: Memoirs of the American Mathematical Society
Publication Year: 2023; Volume 283, Number 1401
ISBNs: 978-1-4704-5994-9 (print); 978-1-4704-7402-7 (online)
DOI: https://doi.org/10.1090/memo/1401
Published electronically: January 20, 2023

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Table of Contents

Chapters

  • Introduction
  • 1. Affine Kac–Moody algebras
  • 2. Crystals and Young walls
  • 3. Young tableaux and almost even tableaux
  • 4. Lattice paths and triangular arrays
  • 5. Dominant maximal weights
  • 6. Weight multiplicities and (spin) rigid Young tableaux
  • 7. Level $2$ weight multiplicities: Catalan and Pascal triangles
  • 8. Level $3$ weight multiplicities: Motzkin and Riordan triangles
  • 9. Some level $k$ weight multiplicities when $k\to \infty$: Bessel triangle
  • 10. Standard Young tableaux with a fixed number of rows of odd length

Abstract

The weight multiplicities of finite dimensional simple Lie algebras can be computed individually using various methods. Still, it is hard to derive explicit closed formulas. Similarly, explicit closed formulas for the multiplicities of maximal weights of affine Kac–Moody algebras are not known in most cases. In this paper, we study weight multiplicities for both finite and affine cases of classical types for certain infinite families of highest weights modules. We introduce new classes of Young tableaux, called the $($spin$)$ rigid tableaux, and prove that they are equinumerous to the weight multiplicities of the highest weight modules under our consideration. These new classes of Young tableaux arise from crystal basis elements for dominant maximal weights of the integrable highest weight modules over affine Kac–Moody algebras. By applying combinatorics of tableaux such as the Robinson–Schensted algorithm and new insertion schemes, and using integrals over orthogonal groups, we reveal hidden structures in the sets of weight multiplicities and obtain explicit closed formulas for the weight multiplicities. In particular we show that some special families of weight multiplicities form the Pascal, Catalan, Motzkin, Riordan and Bessel triangles.

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