Mathematics – Representation Theory
Scientific paper
2007-12-07
Adv. Math. 219 (2008), no. 1, pp. 27-62
Mathematics
Representation Theory
32 pages. Update (August 2010): There is an error in the proof of Theorem 4.7, in this version and the almost-identical publis
Scientific paper
10.1016/j.aim.2008.04.008
We study the orbits of $G=\mathrm{GL}(V)$ in the enhanced nilpotent cone $V\times\mathcal{N}$, where $\mathcal{N}$ is the variety of nilpotent endomorphisms of $V$. These orbits are parametrized by bipartitions of $n=\dim V$, and we prove that the closure ordering corresponds to a natural partial order on bipartitions. Moreover, we prove that the local intersection cohomology of the orbit closures is given by certain bipartition analogues of Kostka polynomials, defined by Shoji. Finally, we make a connection with Kato's exotic nilpotent cone in type C, proving that the closure ordering is the same, and conjecturing that the intersection cohomology is the same but with degrees doubled.
Achar Pramod N.
Henderson Anthony
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