Author : Thomas Lam,Luc Lapointe,Jennifer Morse,Mark Shimozono
Publisher : American Mathematical Soc.
Page : 101 pages
File Size : 40,9 Mb
Release : 2013-04-22
Category : Mathematics
ISBN : 9780821872949
The Poset of $k$-Shapes and Branching Rules for $k$-Schur Functions by Thomas Lam,Luc Lapointe,Jennifer Morse,Mark Shimozono Pdf
The authors give a combinatorial expansion of a Schubert homology class in the affine Grassmannian $\mathrm{Gr}_{\mathrm{SL}_k}$ into Schubert homology classes in $\mathrm{Gr}_{\mathrm{SL}_{k+1}}$. This is achieved by studying the combinatorics of a new class of partitions called $k$-shapes, which interpolates between $k$-cores and $k+1$-cores. The authors define a symmetric function for each $k$-shape, and show that they expand positively in terms of dual $k$-Schur functions. They obtain an explicit combinatorial description of the expansion of an ungraded $k$-Schur function into $k+1$-Schur functions. As a corollary, they give a formula for the Schur expansion of an ungraded $k$-Schur function.