On the quantum Horn problem

Abstract

Let $K$ be a compact, connected, simply-connected simple Lie group. Given two conjugacy classes $\Orb_1$ and $\Orb_2$ in $K$, we consider the multiplicative Horn question: What conjugacy classes are contained in $\Orb_1\cdot\Orb_2$? It is known that answering this question remains to describe a convex polytope $\poly_K$. In 2003, Teleman-Woodward gave a complete list of inequalities for $\poly_K$. Their list contains redundant inequalities. In this paper, we describe $\poly_K$ by a smaller list of inequalities.