Classification of Ding's Schubert varieties: finer rook equivalence
Abstract
K. Ding studied a class of Schubert varieties X_\lambda in type A partial flag manifolds, corresponding to integer partitions \lambda and in bijection with dominant permutations. He observed that the Schubert cell structure of X_\lambda is indexed by maximal rook placements on the Ferrers board B_\lambda, and that the integral cohomology groups H^*(X_\lambda; Zz), H^*(X_\mu; Zz) are additively isomorphic exactly when the Ferrers boards B_\lambda, B_\mu satisfy the combinatorial condition of rookequivalence. We classify the varieties X_\lambda up to isomorphism, distinguishing them by their graded cohomology rings with integer coefficients. The crux of our approach is studying the nilpotence orders of linear forms in the cohomology ring.
 Publication:

arXiv Mathematics eprints
 Pub Date:
 March 2004
 arXiv:
 arXiv:math/0403530
 Bibcode:
 2004math......3530D
 Keywords:

 Mathematics  Algebraic Geometry;
 Mathematics  Combinatorics;
 Mathematics  Geometric Topology;
 14M15;
 05E05
 EPrint:
 19 pages. Final version, with some minor mistakes corrected. To appear in Canadian Journal of Mathematics