We study the varieties of reductions associated to the variety of rank one matrices in $\fgl_n$. These varieties are defined as natural compactifications of the different ways to write the identity matrix as a sum of $n$ rank one matrices. Equivalently, they compactify the quotient of $PGL_n$ by the normalizer of a maximal torus. In particular, we prove that for $n=4$ we get a $12$-dimensional Fano variety with Picard number one, index $3$, and canonical singularities.
@article{hal-00003975,
author = {Iliev, Atanas and Manivel, Laurent},
title = {Varieties of reductions for $gl\_n$},
journal = {HAL},
volume = {2004},
number = {0},
year = {2004},
language = {en},
url = {http://dml.mathdoc.fr/item/hal-00003975}
}
Iliev, Atanas; Manivel, Laurent. Varieties of reductions for $gl_n$. HAL, Tome 2004 (2004) no. 0, . http://gdmltest.u-ga.fr/item/hal-00003975/