On the saturation conjecture for $\operatorname{Spin}(2n)$

Abstract

In this paper we examine the saturation conjecture on decompositions of tensor products of irreducible representations for complex semisimple algebraic groups of type $D$ (the even \emph{spin} groups: Spin$(2n)$ for $n\ge 4$ an integer), extending work done by Kumar-Kapovich-Millson on Spin(8). Our main theorem asserts that the saturation conjecture holds for Spin(10) and Spin(12): for all triples of dominants weights $\lambda,\mu,\nu$ such that $\lambda+\mu+\nu$ is in the root lattice, and for any $N>0$, $$ \left(V(\lambda)\otimes V(\mu)\otimes V(\nu)\right)^G \ne 0 $$ if and only if $$ \left(V(N\lambda)\otimes V(N\mu)\otimes V(N\nu)\right)^G\ne 0, $$ for $G=$ Spin(10) or Spin(12). Some related results for groups of other types are listed as well.