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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

1 vote

How to determine explicit description for a projective variety?

In the context of Kaehler geometry, we have the Kodaira embedding theorem. If you google "Kodaira embedding" you can get lots of good references. See also Huybrechts and Griffiths-Harris.
Kevin H. Lin's user avatar
7 votes

Semisimple quantum cohomology

One reason is Givental's conjecture, which says that in the semisimple case, genus 0 GW invariants determine higher genus GW invariants. See this paper of Teleman, in which the conjecture is proved. …
Kevin H. Lin's user avatar
5 votes
0 answers
678 views

Analysis analogue of Orlov's theorem?

Mukai's theorem states that if $X$ is an abelian variety, and $\check{X}$ is the dual abelian variety, then the Fourier-Mukai transform corresponding to the Poincare line bundle on $X \times \check{X} …
Kevin H. Lin's user avatar
6 votes
Accepted

Why is a partition function of a Topological Conformal Field Theory related to Deligne-Mumfo...

As I said in the comments, you should read AJ's answer to this question. If you haven't read Costello's paper "Topological conformal field theories and Calabi-Yau categories", then you should definit …
Kevin H. Lin's user avatar
7 votes

Crepant resolutions of toric varieties

I googled a bit, and I found a paper "All toric local complete intersection singularities admit projective crepant resolutions" by Dimitrios I. Dais, Christian Haase, and Günter M. Ziegler. It might b …
Kevin H. Lin's user avatar
9 votes

"Points" in algebraic geometry: Why shift from m-Spec to Spec?

There was some discussion about this (and other things) at the secret blogging seminar fairly recently: http://sbseminar.wordpress.com/2009/08/06/algebraic-geometry-without-prime-ideals/
Kevin H. Lin's user avatar
13 votes

A learning roadmap for algebraic geometry

My advice: spend a lot of time going to seminars (and conferences/workshops, if possible) and reading papers. Talk to people, read blogs, subscribe to the arxiv AG feed, etc. AG is a very large field, …
4 votes
1 answer
371 views

Morphisms of Frobenius manifolds: Definitions and examples?

Frobenius manifolds arise in the study of quantum cohomology and mirror symmetry -- roughly they are manifolds (or varieties or whatever) such that the tangent spaces are Frobenius algebras (there are …
Kevin H. Lin's user avatar
5 votes
2 answers
1k views

A very basic question about Abel-Jacobi map

Let $C$ be a compact Riemann surface, let $C^2$ be the cartesian square of $C$, let $J(C)$ be the degree zero Jacobian of $C$, and let $\delta : C^2 \to J(C)$ be the map $(x,y) \mapsto [\mathcal{O}(x- …
Kevin H. Lin's user avatar
10 votes
2 answers
4k views

Symmetric powers of a curve = projective bundle over Jacobian, and the relative version thereof

I am interested in this claim: The $n$th symmetric power $C^{(n)}$ of a genus $g$ curve $C$ is isomorphic to the projectivization $\mathbb{P}(E_n)$ of the sheaf $E_n := \pi_\ast(P_n)$ over the Jacobi …
Kevin H. Lin's user avatar
52 votes
Accepted

Geometric meaning of the Euler sequence on $\mathbb{P}^n$ (Example 8.20.1 in Ch II of Hartsh...

Yes! The geometric picture is very nice and very easy. It is explained on pages 408-409 of Griffiths-Harris. Here is roughly how it works: Let's work over $\mathbb{C}$ for simplicity. Think of $\mat …
Kevin H. Lin's user avatar
21 votes
4 answers
5k views

Extending vector bundles on a given open subscheme, reprise

In this question, Ariyan asks about the question of uniqueness of extensions of vector bundles when they exist. Sasha's answer suggests that extensions of vector bundles don't always exist. More pre …
Kevin H. Lin's user avatar
13 votes
1 answer
2k views

Derived algebraic geometry via dg rings?

Jacob Lurie's stuff seems to develop derived algebraic geometry via $E_\infty$ rings and/or maybe something like simplicial commutative rings. Ben Wieland's comment in this question indicates that Lur …
Kevin H. Lin's user avatar
0 votes

Finding divisors on a curve

Not sure if I understand your question, but here are some generalities. There is a correspondence between line bundles and divisors (you can find this in any algebraic geometry book). There is a cano …
Kevin H. Lin's user avatar
6 votes
Accepted

Can $\mathbb{P}^n$ be regarded as an algebraic vector bundle over some algebraic variety?

Stephen Griffeth's argument works over any field. The total space of a vector bundle is never proper (follows by, e.g., valuative criterion for properness). On the other hand, $P^n$ is always proper. …
Kevin H. Lin's user avatar

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