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arXiv · 1801.09170

Generalized Littlewood-Richardson coefficients for branching rules of GL(n) and extremal weight crystals

Brett Collins
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Abstract

Following the methods used by Derksen-Weyman in \cite{DW11} and Chindris in \cite{Chi08}, we use quiver theory to represent the generalized Littlewood-Richardson coefficients for the branching rule for the diagonal embedding of $\gl(n)$ as the dimension of a weight space of semi-invariants. Using this, we prove their saturation and investigate when they are nonzero. We also show that for certain partitions the associated stretched polynomials satisfy the same conjectures as single Littlewood-Richardson coefficients. We then provide a polytopal description of this multiplicity and show that its positivity may be computed in strongly polynomial time. Finally, we remark that similar results hold for certain other generalized Littlewood-Richardson coefficients.

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Brett Collins. 2018-01-28. Generalized Littlewood-Richardson coefficients for branching rules of GL(n) and extremal weight crystals. https://arxiv.org/abs/1801.09170

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