Degrees of stretched Kostka coefficients

McAllister, Tyrrell B.

Journal of Algebraic Combinatorics, Tome 27 (2008) no. 3, pp. 263-273.

Résumé

Summary: Given a partition $\lambda $ and a composition $\beta $, the stretched Kostka coefficient $K _{ l b}( n) \mathcal $K_$\lambda $beta$(n)$ is the map $n \rightarrowtail K _{ n \lambda , n \beta }$ sending each positive integer $n$ to the Kostka coefficient indexed by $n \lambda $ and $n \beta $. Kirillov and Reshetikhin (J. Soviet Math. $41(2)$, 925-955, 1988) have shown that stretched Kostka coefficients are polynomial functions of $n$. King, Tollu, and Toumazet have conjectured that these polynomials always have nonnegative coefficients (CRM Proc. Lecture Notes 34, 99-112, 2004), and they have given a conjectural expression for their degrees (Séminaire Lotharingien de Combinatoire 54A, 2006). We prove the values conjectured by King, Tollu, and Toumazet for the degrees of stretched Kostka coefficients. Our proof depends upon the polyhedral geometry of Gelfand-Tsetlin polytopes and uses tilings of GT-patterns, a combinatorial structure introduced in De Loera and McAllister, (Discret. Comput. Geom. $32(4)$, 459-470, 2004).

Détail

Classification : 17B10, 52B12
Keywords: keywords Kostka coefficient, representation theory, Gelfand-tsetlin polytope