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

7 votes
Accepted

What is an Oper?

Look at http://arxiv.org/abs/math/0501398 (Opers, Beilinson and Drinfeld, 1993/2005)
Peter LeFanu Lumsdaine's user avatar
1 vote
Accepted

Analytic vs Zariski neighbourhood of a fibre

I don't think the modified question works either. Let $E$ be a general elliptic curve. Take $X$ to be the quotient of $E\times \mathbb{P}^{1}$ by an involution which is a translation by a point of or …
Tony Pantev's user avatar
  • 6,239
4 votes

Reference for the Hodge Bundle

The list of references is way too long. Here are some classical texts containing both the setup and calculations: 1) P. Deligne, Le déterminant de la cohomologie, Current Trends in Arithmetical Algeb …
David Roberts's user avatar
  • 35.5k
2 votes

A useful form of principle of connectedness

EDIT: This is a small correction on the previous argument that I posted here, prompted by a comment of Steven Sam. The question is stable under any base change. Let $\nu : \widetilde{T} \to T$ be the …
Dongryul Kim's user avatar
  • 1,474
7 votes
Accepted

Higgs fields whose determinant have only simple zeros

The statement is easily checked to be true for very stable bundles, so when you look for a counter example you will need to look for a wobbly (i.e. stable but not very stable) bundle. Suppose that $ …
Tony Pantev's user avatar
  • 6,239
2 votes
Accepted

Looking for a good exposition - Rees Construction

There are many excellent references. It really depends on what you are after. One of the most comprehensive references is the thesis of Olivier Penacchio: http://arxiv.org/abs/math/0307156.
Tony Pantev's user avatar
  • 6,239
8 votes

Can Enriques Surfaces have non-trivial TWISTED Fourier-Mukai partners?

There is a natural pair $(X,\alpha)$ that you can construct. Only in this pair $X$ is not a smooth projective variety but is a smooth orbifold surface. If you choose a genus one pencil $Y \to \mathbb{ …
Tony Pantev's user avatar
  • 6,239
16 votes
Accepted

Is $\pi_2$ algebraic?

A slightly better variant of this question is to ask: is the Hurewitz image of $\pi_{2}(X)$ in $H_{2}(X)$ a sub Hodge structure? This is in fact an old question of Philippe Eyssidieux. In section 4.3 …
Tony Pantev's user avatar
  • 6,239
20 votes
Accepted

On a question motivating Lurie's treatment of formal moduli problems

Yes, this has been achieved in some sense. There is a (unpublished and possibly not yet written) work of Gaitsgory and Lurie where they propose an answer to this question. Given a split reductive grou …
Tony Pantev's user avatar
  • 6,239
20 votes

Branch loci of Ramified covers

The branch locus in $Y$ need not be a normal crossings divisor even when $Y$ is a projective space. Suppose $X$ is a smooth complex projective surface with non-abelian fundamental group. By Noether no …
Tony Pantev's user avatar
  • 6,239
2 votes

A question on the topological change of dualizing a SLAG fibration.

I am not completely sure what is meant by this statement since the topology of the torus fibration certainly changes if the fibration doesn't have a section. If on the other hand we follow your prescr …
Tony Pantev's user avatar
  • 6,239
8 votes
Accepted

Hitchin fibration outside of type A

Here is a very brief explanation of what is going on. You can find more details in the papers that Ana lists and in arxiv.org/abs/math/0604617 as you say. If $G$ is a reductive group, the Hitchin ba …
Tony Pantev's user avatar
  • 6,239
16 votes
Accepted

Quasi-unipotent monodromy for general families

Quasi-unipotency is a well defined notion at any point of the discriminant. If we have a proper family $f : X \to S$ of varieties with a smooth total space and a smooth base, and if $p \in D \subset S …
Tony Pantev's user avatar
  • 6,239
11 votes

Examples of Eigensheaves outside of langlands

I am not sure if you will count this but you have the examples from the other side of geometric Langlands. On any smooth variety the skyscraper sheaves of points are eigensheaves for the tensorization …
Tony Pantev's user avatar
  • 6,239
3 votes
Accepted

Genus two pencil in K3 surface

You will get such a pencil of genus two curves provided that the base point of the pencil of lines is not one of the nine points that you blew up to get your $E(1)$. But if the goal was to construct …
Tony Pantev's user avatar
  • 6,239

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