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

3 votes

Examples of the moduli space of X giving facts about a certain X

You have chosen an example where the moduli space (a projective space) is a homogeneous space. So, geometrically, all the objects it parametrises are "the same", and the nature of the moduli space mer …
Charles Matthews's user avatar
3 votes

Which algebraic varieties admit a morphism to a curve?

The question about the projective line seems more fundamental. And geometrically this seems to be about the graphs of rational functions. Certainly the function field of V provides morphisms from a de …
Charles Matthews's user avatar
0 votes
Accepted

Is it possible to approximate a general cubic form by one which factorises?

I would expect not. The reason being that if this is anything like true (products of quadratic forms and and linear forms being dense in the ordinary "strong" or norm topology - presumably what you me …
Charles Matthews's user avatar
6 votes

Life after Hartshorne (the book, not the person)...

Abelian varieties.
13 votes

Elementary examples of the Weil conjectures

The grandfather of all examples is by Gauss: http://en.wikipedia.org/wiki/Weil_conjectures#Background_and_history Of course Gauss didn't mention finite fields other than the prime field. I think it …
Charles Matthews's user avatar
3 votes

Genus of complex projective space

Talking about the arithmetic genus (http://en.wikipedia.org/wiki/Arithmetic_genus), it's the alternating sum of Hodge numbers all of which are 0. So, in short, yes.
Charles Matthews's user avatar
8 votes

Explaining the number field-function field analogy

I think your statement could usefully be sharpened in a couple of ways. Firstly, the state-of-the-art is that true statements for function fields are expected to have analogues for number fields. Th …
Charles Matthews's user avatar
3 votes
Accepted

Polynomials over Z evaluated with finite field arguments

This should work out for you, with a bit more geometry and perhaps a little trickery. You are asking for points over finite fields avoiding a given hypersurface, in affine space. It is conceptually a …
Charles Matthews's user avatar
1 vote
Accepted

graph of elliptic curve inside projective space

I'm not quite sure about the formulation of the question: but there is something worth saying anyway, since it isn't often emphasised in basic texts. The points of order 3 can be identified with the i …
Charles Matthews's user avatar
7 votes

What, if anything, makes homogeneous polynomials so great?

Well, if you are interested in counting solutions mod p, you could note that the "good" formulae are indeed related to the homogeneous approach/projective space. It is not just a question of restoring …
Charles Matthews's user avatar
2 votes

Weil pairing, Kummer theory, help to decrypt what Wikipedia says

The reason Kummer theory is involved is that the Galois covering of an elliptic curve E created by multiplication by n, assuming that n is prime to the characteristic of the base field K, has Galois g …
Charles Matthews's user avatar
2 votes
0 answers
2k views

Who will write the algebraic geometry texts that are needed? [closed]

Readers of MO are probably aware of the pedagogic need that would provoke such a query. It's around 60 years since Serre's FAC, and I imagine some people would say "you still have to read the original …
6 votes
Accepted

Preliminaries for Mumford's Abelian Varieties

To discuss generally first, the book was written up by C. P. Ramanujam, and he was more conscientious than usual in trying to tie down Mumford's lectures to existing references. Still, it is quite har …
Charles Matthews's user avatar
2 votes

Linkage between singularities of algebraic varieties and continued fractions

In the case of Hilbert modular surfaces, continued fractions appeared in the work of Hirzebruch on their singularities. This is easy to find online. This generalises somewhat in Shintani's work, as wa …
Charles Matthews's user avatar
4 votes

Why are topological ideas so important in arithmetic?

If we think about Diophantine equations in general, the situation is "hopeless". That's a theorem. Nevertheless in number theory we want to study such equations, in special cases at least, so some ide …
Charles Matthews's user avatar

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