Isomorphic induced modules and Dynkin diagram automorphisms of semisimple Lie algebras

Consider a simple Lie algebra $\mathfrak{g}$ and $\overline{\mathfrak{g}}$ a Levi subalgebra. Two irreducible $\overline{% \mathfrak{g}}$-modules yield isomorphic inductions to $\mathfrak{g}$ when their highest weights coincide up to conjugation by an element of the Weyl group $W$ of $\mathfrak{g}$ which is also a Dynkin diagram automorphism of $$. In this paper we study the converse problem: given two irreducible $\overline{\mathfrak{g}}$-modules of highest weight $μ$ and $ν$ whose inductions to $\mathfrak{g}$ are isomorphic, can we conclude that $μ$ and $ν$ are conjugate under the action of an element of $W$ which is also a Dynkin diagram automorphism of $\overline{\mathfrak{g}% }$ ? We conjecture this is true in general. We prove this conjecture in type $A$ and, for the other root systems, in various situations providing $μ$ and $ν$ satisfy additional hypotheses. Our result can be interpreted as an analogue for branching coefficient of the main result of \cite{Raj} on tensor product multiplicities.

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