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for questions on geometric invariant theory (or GIT), including stability criteria and symplectic quotients.

1 vote

Bad Categorical Quotients

Let me explain slightly modified example 4.6 by A'Campo-Neuen and Hausen. Suppose that $\mathbb C^*$ acts on $X=\mathbb P^1_{x_1:x_2} \times \mathbb A^2_{y, z}$ (indices denote corresponding coordina …
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0 votes
Accepted

Supposed generalization of $X/(G \times H)\simeq (X/G)/H$ for GIT-quotients

My question should have consisted of two. I will formulated both using linearization via line bundles, not embeddings into projective space, as it makes them more clear. Question 1. Suppose that $\pi …
evgeny's user avatar
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5 votes
1 answer
314 views

Supposed generalization of $X/(G \times H)\simeq (X/G)/H$ for GIT-quotients

I wonder whether it is true that the composition of two GIT-quotients is another GIT-quotient. It should be an analogue of a set-theoretic formula $X/(G \times H)\simeq (X/G)/H$ but with GIT-quotients …
evgeny's user avatar
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4 votes
1 answer
619 views

Vector bundles on quotient variety

Let an algebraic group $G$ act on a complex variety $X$ such that there is a good enough quotient $X/G$ (for example, $G$ acts on a vector space $V$ linearly and $X=V_{ss}$ is a variety of semi-stable …
evgeny's user avatar
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18 votes
1 answer
3k views

Why is Mumford's GIT-quotient so effective?

According to remark 6.14 in Shigeru Mukai's An introduction to invariants and moduli (unfortunately, the page is not available on Google Books, so I explain it below), the GIT-quotient of an affine va …
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