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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

5 votes

explicit uniformizer for the false Tate extension

I think the answer to question Q2 is no. Indeed, Lemma 3 of Birch's paper in Cassels and Fröhlich tells us that two extensions $k(\sqrt[n]{a}),k(\sqrt[n]{b})$ of a field $k$ (of characteristic prime t …
Filippo Alberto Edoardo's user avatar
2 votes
Accepted

Does the Hasse norm theorem easily imply the global squares theorem?

Well, I would say that this crucially depends on what you define to be "quick". If you admit global class field theory, at least in its idelic formulation, the fact that all primes in $K$ are split in …
Filippo Alberto Edoardo's user avatar
0 votes

Decomposition of primes in Galois closures of number fields

The answer is no. Let $K=\mathbb{Q}$ (it does not really matter) and let $M/\mathbb{Q}$ be a degree $6$ extension with Galois group $S_3$; finally, pick for $L$ any of the three cubic subfields of $M$ …
Filippo Alberto Edoardo's user avatar
3 votes

Computing certain class numbers modulo 4

I come later than GH and paul Monsky and with an intricate and way too long answer, but since I had fun in solving the exercice, I post it anyhow. Most probably (as paul Monsky suggested) there are ea …
Filippo Alberto Edoardo's user avatar
5 votes
Accepted

Refinement of (classical) Iwasawa main conjecture

There is an answer which follows from Kolyvagin's theory of Euler Systems, and can be found in Theorem 4.4 of K. Rubin, Kolyvagin's System of Gauss Sums, in Arithmetic Algebraic Geometry, van der Gee …
Filippo Alberto Edoardo's user avatar
0 votes
Accepted

About real abelian number fields

Let $J^{(p)}\subseteq J$ be the subfield fixed by the $p$-Sylow subgroup of $\operatorname{Gal}(J/K)$ which is also the $p$-Sylow subgroup of the (abelian!) group $\operatorname{Gal}(J/\mathbb{Q})$ si …
Filippo Alberto Edoardo's user avatar
6 votes

Ideal classes fixed by the Galois group

As Franz Lemmermeyer suggested, one should consider the so-called Ambigous Class Number Formula: you find it, for instance, in Gras' book "Class Field Theory", II.6.2.3. It says that if $L/K$ is a fi …
Filippo Alberto Edoardo's user avatar
3 votes
Accepted

About principal ideal theorem in number fields

I have been trying to prove the result for a couple of days, without success, so I post what I got in the meanwhile. Let me suppose throughout that $\operatorname{Gal}(E/K)\cong(\mathbb{Z}/p)^2$ (the …
Filippo Alberto Edoardo's user avatar
1 vote
Accepted

A question on Cebotarev's density theorem

Edit: I understand that you are happy with a $T$ which depends upon $L$ and works simultaneously for all $L'/L$ of degree bounded by $d$ and unramified outside of $S_L$. If you are looking for a unifo …
Filippo Alberto Edoardo's user avatar
1 vote

Brauer group of complete DVR

I think an even easier answer (although it should more or less boil down to Ekedahl's) is to apply snake lemma to the following diagram - noting that the middle vertical arrow is an isomorphism $$ 0\t …
Filippo Alberto Edoardo's user avatar
6 votes

Commutative algebra with a view toward algebraic _number theory_

According to Mariano's request, I turn my comment into an answer: I think Neukirch's book "Algebraic Number Theory" might be a good reference. The first part "look reasonably abstract" to be though …
6 votes

An elementary, short proof that the group of units of the ring of integers of a number field...

I do not know if the following qualifies as "short" or "elementary": but it does not follow the usual pattern through Minkowski's Convex Body Theorem. Rather, it mimics the classical proof of Mordell– …
Filippo Alberto Edoardo's user avatar
6 votes
Accepted

The $\ell$- part of the class groups of the $p$-cyclotomic fields

As Keith Conrad observed in his comment, what you are asking about is Washington's theorem which is either in his book, referenced as Theorem 16.12, or in his original paper in Invent. Math. He proved …
Filippo Alberto Edoardo's user avatar
4 votes
Accepted

Class groups in dihedral extensions - some sort of Spiegelungssatz?

I normally don't like to cite my own work on MO, but this time the preprint arXiv:1803.04064 was written, together with L. Caputo, having the OP's question in mind; and so, first of all, let me thank …
Filippo Alberto Edoardo's user avatar
1 vote
Accepted

Kummer congruences for totally real number fields

I think that the point lies in the difference between a primitive and imprimitive $L$-function. Before entering the details, let me observe that Washington's definition of $p$-adic $L$-functions (as t …
Filippo Alberto Edoardo's user avatar

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