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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.
4
votes
2
answers
380
views
How is this surface related to the square of that CM elliptic curve?
I have come across the following surface: let $X$ be the double covering of $\mathbb{P}_\mathbb{Z}^2$ defined by the equation
$$y^2=x_0^6+x_1^6+x_2^6$$
where $y$ is a variable of degree 3.
There is a …
4
votes
0
answers
242
views
Chow groups of arithmetic surfaces
Given an arithmetic surface $S$, I would like to know the following properties of its first and second Chow groups $CH^1(S), CH^2(S)$:
Are they finitely generated? If so, what is the rank?
What is t …
6
votes
3
answers
719
views
When is an affine part of an elliptic curve isomorphic to an affine part of a norm equation?
Given a cubic number field and a basis $\{\gamma_1,\gamma_2,\gamma_3\}$ for it over the rationals, we can write down the norm equation $N(x_1\gamma_1+x_2\gamma_2+x_3\gamma_3)=1$. For almost all substi …
6
votes
1
answer
359
views
Computing the dimensions of representations in a reducible induced representation
This is a question on math.se that got no answers.
1) Is there a relatively general method of computing the dimensions of representations in a reducible induced representation?
An explicit specific …
29
votes
1
answer
2k
views
Is the Brauer group of a surface an elliptic curve?
Of course not.
But after reading a bit, some points make me believe it should be:
Let $S$ be a nice$^{\*}$ surface defined over $Spec\ \mathbb{Z}$.
The Brauer group $Br(S\otimes \bar{\mathbb{Q}})$ …
3
votes
1
answer
246
views
Is this unipotent group, over characteristic 2, connected?
Let $E_{ij}(x)\in \mathrm{Mat}_{7\times7}(\overline{\mathbb{F}}_2)$ be the matrix with zeros everywhere, except for the value $x$ at $ij$. Set $$a(x)=1+E_{12}(x)+E_{34}(x)+E_{56}(x),\quad b(y)=1+E_{23 …
7
votes
0
answers
486
views
What is the right basis of solutions of the Picard-Fuchs equation of the Legendre family aro...
I have been trying to reconstruct some elliptic curves theory computationally and have gotten stuck on some period computations.
Specifically, let $$E_\lambda:\ y^2=x(x-1)(x-\lambda)$$ be the Legendr …
0
votes
Upper bound on greatest prime of bad reduction for a plane curve
The primes that are "bad" in your sense will divide the number $Res_x(Res_y(f,\frac{\partial f}{\partial x}), Res_y(f,\frac{\partial f}{\partial y}))$. (If I interpreted damiano's comment correctly).
…
3
votes
2
answers
377
views
Upper bound on greatest prime of bad reduction for a plane curve
Background
We are given a curve with integer coefficients. I want to make a suggestion in another question (Computationally bounding a curve's genus from below?) into a deterministic algorithm for fi …
11
votes
1
answer
562
views
CM field to Torus to Abelian Variety?
Given a CM field we can use its maximal order (and a choice of CM type) to construct an abelian variety $\mathbb{C}^g/\Lambda$ with complex multiplication by the maximal order.
How do I (or where can …
10
votes
3
answers
633
views
Computationally bounding a curve's genus from below?
Background
In the course of answering another question (Infinite collection of elements of a number field with very similar annihilating polynomials) I found myself with a curve, that if it had a pos …
29
votes
2
answers
4k
views
What is the algebraic closure of the field with one element?
If doing geometry over $\mathbb F_p$ means also using its algebraic closure, it must be interesting to talk about the algebraic closure of $\mathbb F_1$ - the field with one element.
I saw that the f …
26
votes
7
answers
6k
views
When is a product of elliptic curves isogenous to the Jacobian of a hyperelliptic curve?
David's question Families of genus 2 curves with positive rank jacobians reminded me of a question that once very much interested me: when is a product of elliptic curves isogenous to the jacobian of …
1
vote
1
answer
802
views
Is the direct limit of Weil restriction of an elliptic curve a scheme?
In a discussion today on the Shafarevich-Tate group of an elliptic curve, the following structure and question came up. I will abuse many notations and be very vague about some things, but am very ope …
4
votes
2
answers
436
views
Can an abelian variety be represented as the cohomology of some other object?
Question
Given an abelian variety $V$ and an integer $n$, is there a natural abelian category with a natural object $X$ and natural coefficients $F$ so that $V\simeq H^n (X,F)$?
Motivation
Studying …