T-equivariant cohomology of cell complexes and the case of infinite Grassmannians

Singular BGG complexes over isotropic 2-Grassmannian

We construct exact sequences of invariant differential operators acting on sections of certain homogeneous vector bundles in singular infinitesimal character, over the isotropic $2$-Grassmannian. This space is equal to $G/P$, where $G$ is $\operatorname{Sp}(2n,\mathbb{C})$, and $P$ its standard parabolic subgroup having the Levi factor $\operatorname{GL}(2,\mathbb{C}) \times \operatorname{Sp}(2n-4,\mathbb{C})$. The constructed sequences are analogues of the Bernstein-Gelfand-Gelfand resolutions. We do this by considering the Penrose transform over an appropriate double fibration. The result di…

格拉斯曼流形与旗流形的最小等变嵌入

Minimal equivariant embeddings of the Grassmannian and flag manifold

本文证明旗流形（含格拉斯曼流形）存在维数为$(n-1)(n+2)/2$的SO_n等变嵌入，该维数最小且所有最小维等变嵌入均等价。

Equivariant torsion and G-CW-complexes

For any compact Lie group G we discuss the relation of the equivariant Reidemeister and analytic torsion of G-manifolds with their G-CW structures.

Complex $\text{G}_2$ and Associative Grassmannian

We obtain defining equations of the smooth equivariant compactification of the Grassmannian of the complex associative $3$-planes in $\C^7$, which is the parametrizing variety of all quaternionic subalgebras of the algebra of complex octonions $\OO\cong \C^8$. By studying the torus fixed points, we compute the Poincaré polynomial of the compactification.

Polygon spaces and Grassmannians

We study the moduli spaces of polygons in R^2 and R^3, identifying them with subquotients of 2-Grassmannians using a symplectic version of the Gel'fand-MacPherson correspondence. We show that the bending flows defined by Kapovich-Millson arise as a reduction of the Gel'fand-Cetlin system on the Grassmannian, and with these determine the pentagon and hexagon spaces up to equivariant symplectomorphism. Other than invocation of Delzant's theorem, our proofs are purely polygon-theoretic in nature.

Singular BGG complexes for the symplectic case

Using the Penrose transform, we construct analogues of the BGG (Bernstein-Gelfand-Gelfand) resolutions in certain singular infinitesimal characters, in the holomorphic geometric setting, over the Lagrangian Grassmannian. We prove the exactness of the constructed complex over the big affine cell.