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Prime numbers, diophantine equations, diophantine approximations, analytic or algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions
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 $Br(S\otimes \bar{\mathbb{Q}})$ …
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 …
28
votes
Accepted
Why does the definition of modularity demand weight 2?
$\newcommand\Q{\mathbf{Q}}$
$\newcommand\Qbar{\overline{\Q}}$
$\newcommand\Gal{\mathrm{Gal}}$
$\newcommand\C{\mathbf{C}}$
$\newcommand\Sym{\mathrm{Sym}}$
$\newcommand\E{\mathcal{E}}$
$\newcommand\Bett …
27
votes
5
answers
3k
views
Class number measuring the failure of unique factorization
The statement that the class number measures the failure of the ring of integers to be a ufd is very common in books. ufd iff class number is 1. This inspires the following question:
Is there a quant …
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 …
25
votes
1
answer
1k
views
When does a modular form satisfy a differential equation with rational coefficients?
Given a modular form $f$ of weight $k$ for a congruence subgroup $\Gamma$, and a modular function $t$ with $t(i\infty)=0$, we can form a function $F$ such that $F(t(z))=f(z)$ (at least locally), and w …
18
votes
1
answer
2k
views
Galois representations attached to Maass form
So, how does one construct a galois representation from a Maass form?
For a modular cusp eigenform, I am familiar with the work of Eichler-Shimura, Deligne, Deligne-Serre, and realize these are diffe …
17
votes
5
answers
3k
views
Families of number fields of prime discriminant
When I am testing conjectures I have about number fields, I usually want to control the ramification, especially minimize to a single prime with tame ramification. Hence, I usually look for fields of …
16
votes
4
answers
1k
views
Geometric meaning of fiber of modular parameterization over a point of an elliptic curve?
Given an elliptic curve $E/\mathbb{Q}$ of conductor $N$, parameterization $\psi : X_0(N) \rightarrow E$, and a point $P \in E$, take the fiber $\psi^{-1}(P)$. Its points, being on $X_0(N)$, correspond …
14
votes
2
answers
2k
views
Irreducible polynomial over number field with roots in every completion?
Let K/Q be a field, probably not a finite extension. Is it possible for a polynomial to be irreducible over K but have a root in every completion of K? What about all but finitely many completions?
T …
13
votes
Accepted
Upper bound of period length of continued fraction representation of very composite number s...
The continued fraction length is usually a small constant factor away from the regulator. A more precise version can also be achieved, but I don't remember a reference, so if anyone does...
Then, we …
12
votes
Accepted
Examples of Galois-invariant central simple algebras which aren't base change?
[big edit]
(1) Let $L/K$ be as above. Take any non-identity element $\sigma \in G_{L/K}$, and let $F=L^{<\sigma>}$ be the fixed field of the cyclic subgroup generated by $\sigma$. By your comment abo …
12
votes
0
answers
747
views
What is the Shafarevich-Tate group of GL(2)?
Let $K$ be a number field, $\bar{K}$ a fixed algebraic closure, $G_K$ the absolute galois group, $O_\bar{K}$ the ring of integers of the algebraic closure, $\mathfrak{p}$ runs over prime ideals and su …
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 …
11
votes
2
answers
911
views
Density of monogenic number fields?
Background
Zev Chonoles recently asked the question "which number fields are monogenic?". The answers say that for a specific number field the question is hard. So, I thought, how about looking at al …