Tagged Questions

3
votes
1answer
277 views

A cohomology computation request.

The short: Let $X= \{(x,y,z) \in \mathbb{C}^* \times \mathbb{C} \times \mathbb{C} \, |\, yz-x\neq 0\}$ Compute $H^*_c(X)$ (say with $\mathbb{C}$-coefficients). The long: Unless …
3
votes
1answer
125 views

“Degree” of a Fano Scheme of a projective variety

Consider subschemes $F$ of the Grassmannian $\mathbb{G}(k,n)$ satisfying the condition that each point of $\mathbb{P}^n$ is contained in only finitely many of the $k$-planes in $F$ …
8
votes
1answer
248 views

Schubert varieties which admit small resolutions of singularities

I am looking for an (incomplete) list of partial flag varieties for which all Schubert cells admit small resolutions of singularities. This is interesting, for many reasons. My m …
4
votes
1answer
167 views

Minimal relative Schubert modules

I am trying to better understand the definition of certain objects called minimal relative Schubert modules. My primary reference is Chapters 1 and 2 of Wilberd van der Kallen's Le …
3
votes
0answers
330 views

Schubert varieties of flag variety , perverse sheaves

The set of Schubert varieties in a flag variety is in one-to-one correspondence with elements of the Weyl group via left cells. There is also some relation between products of Sch …
10
votes
1answer
353 views

Do Richardson varieties have rational singularities in arbitrary characteristic?

The title basically asks the question. I'll review the relevant terminology and explain what I have and haven't found in the literature. Let $G$ be a reductive group. Let $v \leq …
0
votes
0answers
140 views

Codimension of a Schubert cell and number of equations.

Let $G(n, X)$ be the set of all $n$-dim subspaces of a $n+m$-dim vector space $X$. $$ 0=F_0 \subset F_1 \subset \cdots \subset F_{n+m-1} \subset F_{n+m} = X $$ is a fixed compl …
8
votes
2answers
584 views

Expository treatment of Schubert Cells Paper

I was wondering about the paper by Bernstein, Gel'fand, and Gel'fand on Schubert Cells. This paper is fairly old(and often cited) so I figured someone must have represented this ma …
2
votes
1answer
152 views

Can we see the geometric realization of $U_q(sl_2)$'s relations as Schubert Conditions?

In Nakajima's Geometric construction of algebras(pages 3-7), he uses the subalgebra of the convolution algebra of $Gr(k^N)\times Gr(k^N)$ invariant under $GL_N$ action to construct …
6
votes
1answer
531 views

What functor does a Schubert variety represent?

I'm inspired by Yuhao's question. The functor that takes a scheme S to the set of k-dimensional vector subbundles of C^n x S (understanding "subbundle" to mean that the quotient b …
6
votes
2answers
402 views

Richardson varieties over finite fields

Let me start with some background to set the notation before I ask my question. Let G be a semisimple algebraic group over some algebraically closed field K, and suppose we have f …
0
votes
0answers
86 views

Existence of a Ramification of a Linear Subspace

Question and background I have started reading the paper Frontiers of Reality in Schubert Calculus. On page 5 near the bottom of the page, the author picks a subspace of a Grassma …