Components of $V(\rho )\otimes V(\rho )$ and dominant weight polyhedra for affine Kac-Moody Lie algebras

Kostant asked the following question: Let $\mathfrak{g}$ be a simple Lie algebra over the complex numbers. Let $\lambda$ be a dominant integral weight. Then, $V(\lambda )$ is a component of $V(\rho )\otimes V(\rho )$ if and only if $\lambda \le 2\rho$ under the usual Bruhat-Chevalley order on the set of weights. In an earlier work with R. Chirivi and A. Maffei the second author gave an affirmative answer to this question up to a saturation factor. The aim of the current work is to extend this result to untwisted affine Kac-Moody Lie algebra $\mathfrak{g}$ associated to any simple Lie algebra $\mathring{\mathfrak{g}}$ (up to a saturation factor). In fact, we prove the result for affine $s{l}_n$ without any saturation factor. Our proof requires some additional techniques including the Goddard-Kent-Olive construction and study of the characteristic cone of non-compact polyhedra.