Tensor invariants, Saturation problems, and Dynkin automorphisms

Abstract

Let G be a connected almost simple algebraic group with a Dynkin automorphism {\sigma}. Let G_{\sigma} be the connected almost simple algebraic group associated to G and {\sigma}. We prove that the dimension of the tensor invariant space of G_{\sigma} is equal to the trace of {\sigma} on the corresponding tensor invariant space of G. We prove that if G has the saturation property then so does G{\sigma}. As a consequence, we show that the spin group Spin(2n + 1) is of saturation property with factor 2, which strengthens the results of Belkale-Kumar and Sam in the case of type B_n.