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Algebraic number fields, Algebraic integers, Arithmetic Geometry, Elliptic Curves, Function fields, Local fields, Arithmetic groups, Automorphic forms, zeta functions, $L$-functions, Quadratic forms, Quaternion algebras, Homogenous forms, Class groups, Units, Galois theory, Group cohomology, Étale cohomology, Motives, Class field theory, Iwasawa theory, Modular curves, Shimura varieties, Jacobian varieties, Moduli spaces

1 vote
1 answer
636 views

About points on affine curves defined over finite fields

So let $\mathbf{F}_q$ be a finite field with $q$ elements where $q=p^m$, $p$ a prime number and $m\in\mathbf{Z}_{\geq 1}$. Let $f(x,y)\in \mathbf{F}_q[x,y]$ be a smooth non-constant polynomial and …
Hugo Chapdelaine's user avatar
7 votes
2 answers
344 views

explicit uniformizer for the false Tate extension

Let $p$ be an odd prime and let $n\geq 1$. Set $K=\mathbb{Q}_p(\zeta_{p^n})$, $L=\mathbb{Q}_p(\sqrt[p^n]{p})$, and $M=KL$. I claim that $M$ is totally ramified of degree $\phi(p^n)p^n$ (the proof simu …
Hugo Chapdelaine's user avatar
12 votes
1 answer
774 views

Intersection of a ring class field of a quadratic field K with the cyclotomic extension of K

Let $K$ be a quadratic field. Let $f\in\mathbb{Z}_{\geq 1}$. Let $\mathcal{O}_f=\mathbf{Z}+f\mathcal{O}_K$ be the unique order of $K$ of index $f$ in $\mathcal{O}_K$. Let $H_f^{ring}$ denote the ring …
Hugo Chapdelaine's user avatar
3 votes
2 answers
531 views

What is the exact meaning of the real period in the $p$-adic formulation of BSD?

Let $E$ be an elliptic curve over $\mathbf{Q}$ which has split multiplicative reduction at $p$ (a prime). If one chooses a global Neron model of $E$ over $\mathbf{Z}$ (unique up to unique isomorphism …
Hugo Chapdelaine's user avatar
9 votes
2 answers
3k views

Is there a Riemann-Roch for smooth projective curves over an arbitrary field?

Let $X$ be a smooth projective curve over a field $k$. We let $\omega$ be the canonical line bundle of $X$ and we denote by $F$ the field of $k$-valued rational functions on $X$. (1) When $k$ is alg …
Hugo Chapdelaine's user avatar
5 votes
1 answer
1k views

Effective Chebotarev density results for arbitrary number fields

So let $f(x)\in\mathbf{Z}[x]$ be a monic polynomial of degree $d$ and let $K$ be the splitting field of $f$. Let us define the "heigt of $f$" $:=||f||$ to be the maximum of the abolute values of the …
5 votes
0 answers
392 views

What is the shape of the zeta function of a singular hypersurface?

So let $X$ be a projective hypersurface inside $\mathbb{P}_{\mathbb{Z}}^n$ of degree $d$. Assume that (a) $X(\mathbb{C})$ and $X(\overline{\mathbb{F}}_p)$ are irreducible, (b) and that $X(\mathbb{C …
Hugo Chapdelaine's user avatar
6 votes
4 answers
2k views

Criteria for topologically finitely generated profinite groups

Q1: Do we have a criterion which allows us to say when is a profinite group $G$ topologically finitely generated? For example, if $G$ is topologically finitely generated then, for a fixed integer $N$ …
Hugo Chapdelaine's user avatar
2 votes
1 answer
214 views

Criteria for the surjectivity of the reduction map of the $SL_n$-group scheme

Let $R$ be a commutative ring and let $I\subseteq R$ be an ideal. We have a natural projection map $$ \pi:SL_n(R)\rightarrow SL_n(R/I) $$ (In the original question I had put $GL_n$ instead of $SL_n$ w …
Hugo Chapdelaine's user avatar
1 vote

Criteria for the surjectivity of the reduction map of the $SL_n$-group scheme

The answers to Q2 and Q3 are positive. See Luc Guyot comment in the following MO Question: When is $SL(n,R) \rightarrow SL(n,R/q)$ surjective? In general, if $R$ is a noetherian one dimensional dom …
Hugo Chapdelaine's user avatar
5 votes
2 answers
806 views

On Weil's characters of type (A)

In Weil's paper "On a certain type of characters of the idele-class group of an algebraic number field", Weil introduces a class of characters on the Idele class group (of not necessarily finite o …
Hugo Chapdelaine's user avatar
3 votes
0 answers
142 views

$\mathbb{Z}$-linear independence of arguments of units in non-CM number fields

Playing a little bit with Groessencharacters a stumbled on the following question: Let $K$ be a non CM number field with $r_1$ real embeddings and $2r_2>0$ complex embeddings. Set $r=r_1+r_2-1$ and a …
Hugo Chapdelaine's user avatar
2 votes
1 answer
461 views

On the conductor of the Groessencharacter of a CM elliptic curve

Let $K$ be a quadratic imaginary field. Let $L$ be a number field which contains $K$ and let $E/L$ be an elliptic curve defined over $L$ with complex multiplication by $K$, i.e. such that $End_{\overl …
Hugo Chapdelaine's user avatar
3 votes
Accepted

Fields generated by torsion points of CM elliptic curves

The proof of Corollary 1.7 is fine. I had misunderstood his proof. His proof uses in a crucial way his assumption (ii) which appears on the top of p. 41. As is explained on p. 41, this assumption impl …
Hugo Chapdelaine's user avatar
5 votes
4 answers
682 views

Examples of discrete subgroups of $PSL_2(\mathbf{R})$ with finite covolume and which are not...

Is there a natural example of a discrete subgroup $\Gamma\leq PSL_2(\mathbf{R})$ such that (1) $\Gamma$ has finite covolume (2) $\mathfrak{h}/\Gamma$ is not compact ($\mathfrak{h}$ being the upper h …
Hugo Chapdelaine's user avatar

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