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9 votes
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Closures of torus orbits in flag varieties

Consider the Lie group $G=SL_n(\mathbb C)$ with Borel subgroup $B$ and maximal torus $T\subset B$. I'm interested in the (Zariski) closures of $T$-orbits in the flag variety $F=G/B$. Now, as far as I …
Igor Makhlin's user avatar
  • 3,513
6 votes
2 answers
304 views

Irreducibility of Gelfand-Serganova strata

To keep the notations simple I'll restrict my attention to the complete flag variety although the question should be equally valid for partial flag varieties. Consider $G=SL_n(\mathbb C)$ with Borel $ …
Igor Makhlin's user avatar
  • 3,513
4 votes
Accepted

geometric meaning to pairs of SYT indexing for the basis of cohomology ring of full flag var...

Since, surprisingly, there are still no answers or even comments, let me note that the answer to the last question is well known to be "yes": the Schubert cell containing a flag $(E_1,\dots,E_m)$ is i …
Igor Makhlin's user avatar
  • 3,513
3 votes
0 answers
103 views

A "Dynkin diagram locality" property of flag varieties

For $n\ge 2$ consider the set of Plücker variables $X_{i_1,\dots,i_k}$ with $1\le k\le n-1$ and $1\le i_1<\dots<i_k\le n$ and the ring $R$ of polynomials in these variables (with complex coefficients) …
Igor Makhlin's user avatar
  • 3,513
3 votes
Accepted

Containment of Bruhat cells on flag variety

I'd say that the relevant fact here is as follows. For two Borels $B_1$ and $B_2$ with a common maximal torus $T$ let $x_1$ be the unique $T$-fixed point in the open $B_1$-orbit. Then the $B_2$-orbit …
Igor Makhlin's user avatar
  • 3,513
3 votes

Union of Schubert cells being affine

This is essentially an extension of my comment, just to answer the actual "is this the only case?" question. It is not, $Z$ will be affine whenever $S$ is an antichain in the Bruhat order. Indeed, thi …
Igor Makhlin's user avatar
  • 3,513
3 votes
0 answers
161 views

Defining ideal of a Schubert variety as a kernel

Consider the Plücker embedding of the variety of complete flags in $\mathbb C^n$: $$F_n\subset\mathbb P(\bigwedge\nolimits^1\mathbb C^n)\times\dots\times\mathbb P(\bigwedge\nolimits^{n-1}\mathbb C^n). …
Igor Makhlin's user avatar
  • 3,513
1 vote

Embeddings of flag manifolds

Victor Petrov essentially answered your question showing that this projective embedding is, in general, not minimal. I'll just try to explain why this other embedding is, in fact, minimal by dimension …
Igor Makhlin's user avatar
  • 3,513