Special and general types
Cohomology and Extensions
Schubert calculus is a formal calculus in enumerative geometry, which geometrically reduces to the combinatorics and intersection theory of so-called Schubert cells in Grassmannians.
Schubert calculus is concerned with the ring structure on the cohomology of flag varieties and Schubert varieties. Traditionally this is considered for ordinary cohomology (see References – traditional) later also for generalized cohomology theories (see References – In generalized cohomology), notably in complex oriented cohomology theory such as K-theory, elliptic cohomology and algebraic cobordism.
The rigorous foundations of Schubert calculus is the content of 15th of Hilbert's problems.
Flag varieties and Schubert varieties
The basic data to be fixed is a sequence of inclusions
Correspondences, pull-push and Schubert classes
From the above data one obtains homomorphisms of spaces with -action forming correspondences (“generalized twistor correspondence”)
e.g. (Ganter-Ram 12, p.4)
For fiber integration in generalized cohomology theories along these maps see (Ganter-Ram 12, 4.1)
be the inclusion of the Schubert varieties, then push-forward of the unit classes allong these inclusions defined Schubert classes
(Ganter-Ram 12, 5)
For equivariant K-theory this is discussed in (Ganter 12, 8.2). For equivariant elliptic cohomology in (Ganter 12, 8.3)
With Schubert classes defines as above in a multiplicative cohomology theory, the Schubert product formula is
for some coefficients , to be determined.
(Ganter-Ram 12, 6)
[eom]: Frank Sotile, Schubert calculus
wikipedia Schubert calculus
H. Schubert, Kalkül der abzählenden Geometrie, Springer (1879) (Reprinted (with an introduction by S. Kleiman): 1979), MR0555576
S.L. Kleiman, D. Laksov, Schubert calculus, Amer. Math. Monthly 79 (1972) pp. 1061–1082, MR0323796, jstor
In generalized cohomology theory
Discussion of Schubert calculus in generalized cohomology theories is in
- Paul Bressler, Sam Evens. The Schubert calculus, braid relations, and generalized cohomology. Trans. Amer. Math. Soc., 317(2):799–811, 1990
Paul Bressler, Sam Evens, Schubert calculus in complex cobordism Trans. Amer. Math. Soc., 331(2):799–813, 1992
Baptiste Calmès, Victor Petrov, Kirill Zainoulline, Invariants, torsion indices and oriented cohomology of complete flags May 200 (web)
Jens Hornbostel, Valentina Kiritchenko, Schubert calculus for algebraic cobordism. J. Reine Angew. Math., 656:59–85, 2011
Nora Ganter, Arun Ram, Generalized Schubert calculus, (arxiv/1212.5742)
Nora Ganter, The elliptic Weyl character formula (arXiv:1206.0528)
Revised on October 31, 2013 00:52:08
by Urs Schreiber