On Orbital variety closures in sl_n. III Geometric properties

Abstract

This is the third paper in the series. Here we define a few combinatorial orders on Young tableaux. The first order is obtained from induced Duflo order by the extension with the help of Vogan T_{α, β} procedure. We call it Duflo-Vogan order. The second order is obtained from the generalization of Spaltenstein's construction by consideration of an orbital variety as a double chain of nilpotent orbits. We call it the chain order. Again, we use Vogan's T_{α, β} procedure, however, this time to restrict the chain order. We call it Vogan-chain order. The order on Young tableaux defined by the inclusion of orbital variety closures is called a geometric order and the order on Young tableaux defined by inverse inclusion of primitive ideals is called an algebraic order. We get the following relations between the orders: Duflo-Vogan order is an extension of the induced Duflo order; the algebraic order is an extension of Duflo-Vogan order; the geometric order is an extension of the algebraic order; Vogan-chain order is an extension of the geometric order; and, finally, the chain order is an extension of Vogan-chain order. The computationsshow that Duflo-Vogan and Vogan-chain orders coincide on sl_n for n<10 and in n=10 there is one case (up to T_{α,β} procedure and transposition) where Vogan-chain order is a proper extension of Duflo-Vogan order. In this only case the algebraic order coincides with Vogan-chain order. These computations permit us to conjecture that in sl_n the algebraic order coincides with the geometric order. As well we conjecture that the combinatorics of both the inclusions on primitive ideals and on orbital variety closures is defined by Vogan-chain order on Young tableaux.