A diagrammatic approach to Kronecker squares (1310.8362v2)

Abstract: In this paper we apply a method of Robinson and Taulbee for computing Kronecker coefficients together with other ingredients and show that the multiplicity of each component in a Kronecker square can be obtained from an evaluation of a certain polynomial, which depends only on the component and is computed combinatorially. This polynomial has as many variables as the set of isomorphism classes of connected skew diagrams of size at most the depth of the component. We present two applications. The first is a contribution to Saxl conjecture, which asserts that the Kronecker square of the staircase partition, contains every irreducible character of the symmetric group as a component. We prove that for any partition there is a piecewise polynomial function in one real variable such that for all k, such that the multiplicity of this partition in the Kronecker square of the staircase partition of size k is given by the evaluation of the polynomial function in k. The second application is a proof of a new stability property for Kronecker coefficients.