Weight Diagrams of $gl(m|n)$ Modules

Abstract

Many properties of simple finite dimensional gl(m|n)-modules may be better understood by assigning weight diagrams to the highest weights with respect to a given base of simple roots. In this paper we consider bases that are compatible with the standard Borel subalgebra in $gl(m|n)_0 = gl(m) \times gl(n)$; namely, the bases that differ from the distinguished base $\Sigma^{dist}$ of simple roots by a sequence of odd reflections. We examine the weight diagrams that arise from the highest weights of a simple module $L(\lambda)$ with respect to such bases. Further, we provide combinatorial tools to describe all the weight diagrams of highest weights of $L(\lambda)$ provided only with the the weight diagram of $L(\lambda)$ with respect to distinguished highest weight $\lambda$. Finally, we study the maximal cardinality of incomparable sets of positive odd roots with respect to $\Sigma^{dist}$ which are orthogonal to some highest weight of $L(\lambda)$ with respect to a base as above. We provide explicit formulas for this value, connecting it to the combinatorics of the weight diagrams. Based on this study, we respond to the work of M. Gorelik and Th. Heidersdorf, providing a counterexample to their Tail Conjecture.