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Affine insertion and Pieri rules for the affine Grassmannian

About this Title

Thomas Lam, Department of Mathematics, Harvard University, Cambridge MA 02138 USA, Luc Lapointe, Instituto de Matemática Y Física, Universidad de Talca, Casilla 747, Talca, Chile, Jennifer Morse, Department of Mathematics, Drexel University, Philadelphia, Pennsylvania 19104 and Mark Shimozono, Department of Mathematics, Virginia Tech, Blacksburg, Virginia 24061

Publication: Memoirs of the American Mathematical Society
Publication Year: 2010; Volume 208, Number 977
ISBNs: 978-0-8218-4658-2 (print); 978-1-4704-0591-5 (online)
DOI: https://doi.org/10.1090/S0065-9266-10-00576-4
Published electronically: April 28, 2010
Keywords: Tableaux, Robinson-Schensted insertion, Schubert calculus, Pieri formula, affine Grassmannian
MSC: Primary 05E05, 14N15

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Table of Contents

Chapters

  • Introduction
  • 1. Schubert Bases of $\mathrm {Gr}$ and Symmetric Functions
  • 2. Strong Tableaux
  • 3. Weak Tableaux
  • 4. Affine Insertion and Affine Pieri
  • 5. The Local Rule $\phi _{u,v}$
  • 6. Reverse Local Rule
  • 7. Bijectivity
  • 8. Grassmannian Elements, Cores, and Bounded Partitions
  • 9. Strong and Weak Tableaux Using Cores
  • 10. Affine Insertion in Terms of Cores

Abstract

We study combinatorial aspects of the Schubert calculus of the affine Grassmannian $\textrm {Gr}$ associated with $SL(n,\mathbb {C})$. Our main results are:

  • Pieri rules for the Schubert bases of $H^*(\textrm {Gr})$ and $H_*(\textrm {Gr})$, which expresses the product of a special Schubert class and an arbitrary Schubert class in terms of Schubert classes.
  • A new combinatorial definition for $k$-Schur functions, which represent the Schubert basis of $H_*(\textrm {Gr})$.
  • A combinatorial interpretation of the pairing $H^*(\textrm {Gr})\times H_*(\textrm {Gr}) \rightarrow \mathbb Z$ induced by the cap product.
  • These results are obtained by interpreting the Schubert bases of $\textrm {Gr}$ combinatorially as generating functions of objects we call strong and weak tableaux, which are respectively defined using the strong and weak orders on the affine symmetric group. We define a bijection called affine insertion, generalizing the Robinson-Schensted Knuth correspondence, which sends certain biwords to pairs of tableaux of the same shape, one strong and one weak. Affine insertion offers a duality between the weak and strong orders which does not seem to have been noticed previously.

    Our cohomology Pieri rule conjecturally extends to the affine flag manifold, and we give a series of related combinatorial conjectures.

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