旗流形上的一些真实与不真实的计数几何

Pfaff系统旗帜的不等式与计数公式

Inequalities and enumerative formulas for flags of Pfaff systems

本文研究了Pfaff系统在复射影空间上的旗帜不等式与计数公式，推导了与度数相关的不等式，并证明了某些全纯可积分布的稳定性结果。

Some applications of localization to enumerative problems

A simple corollary of the localization theorem (due to the author and, independently, to Lian-Liu-Yau) is applied to several problems in enumerative geometry. New formulas for Schubert calculus on flag manifolds, due to Kong, and a new reconstruction theorem for genus-zero Gromov-Witten invariants, due to Bertram-Kley, are discussed, as well as some simple functorial properties of Givental's J-function. This paper will appear in the issue of the Michigan Mathematical Journal dedicated to Bill Fulton.

Real enumerative geometry and effective algebraic equivalence

We describe an approach to the question of finding real solutions to problems of enumerative geometry, in particular the question of whether a problem of enumerative geometry can have all of its solutions be real. We give some methods to infer one problem can have all of its solutions be real, given that a related problem does. These are used to show many Schubert-type enumerative problems on some flag manifolds can have all of their solutions be real.

Quantum cohomology of flag manifolds

The (small) quantum cohomology ring of a flag manifold F encodes enumerative geometry of rational curves on F. We give a proof of the presentation of the ring and of a quantum Giambelli formula, which is more direct and geometric than the previously known proof. Furthermore, this proof gives a relationship between quantum Schubert polynomials and universal Schubert polynomials, which arise in a degeneracy locus formula of Fulton.

On the cohomology rings of real flag manifolds: Schubert cycles

We give an algorithm to compute the integer cohomology groups of any real partial flag manifold, by computing the incidence coefficients of the Schubert cells. For even flag manifolds we determine the integer cohomology groups, by proving that any torsion class has order 2 (generalizing a result of Ehresmann). We conjecture this to hold for any real flag manifold. We obtain results concerning which Schubert varieties represent integer cohomology classes, their structure constants and how to express them in terms of characteristic classes. For even flag manifolds and Grassmannians we also descr…

Halving spaces and lower bounds in real enumerative geometry

We develop the theory of halving spaces to obtain lower bounds in real enumerative geometry. Halving spaces are topological spaces with an action of a Lie group $Γ$ with additional cohomological properties. For $Γ=\mathbb{Z}_2$ we recover the conjugation spaces of Hausmann, Holm and Puppe. For $Γ=\mathrm{U}(1)$ we obtain the circle spaces. We show that real even and quaternionic partial flag manifolds are circle spaces leading to non-trivial lower bounds for even real and quaternionic Schubert problems. To prove that a given space is a halving space, we generalize results of Borel and Haeflige…