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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

9 votes
1 answer
550 views

Absolute values of non-unit algebraic integers at all infinite places

Let $K$ be a number field and $O_K$ its ring of integers. Given any non-unit element $\alpha\in O_K$, does there exist a unit $u\in O^\times_K$ such that $$ |\sigma(u \alpha)| >1 \quad \text{ for all …
J.Li's user avatar
  • 1,053
2 votes
1 answer
438 views

class field theory for K-groups of number fields

Let $F$ be a number field. The classical class field theory gives an isomorphism between the ideal class group $Cl(F)$ and $\mathrm{Gal}(H/F)$, where $H$ is the Hilbert class field (maximal unramifie …
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  • 1,053
9 votes

Are quadratic units cyclotomic norms?

Edit:Let $K=\mathbb Q(\zeta_p)^+$ Since it's easy to show $-1 \in N(\mathcal O_K ^{\times})$ and $\mathrm{Gal}(K/k)$ is cyclic, your question is equivalent to ask whether $\mathrm{H}^2(K/k,\mathcal O …
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  • 1,053
1 vote

Generalized Greenberg's conjecture for imaginary quadratic fields

Let $K=\mathbb{Q}(\sqrt{-q})$ where $q\equiv 7\bmod 16$ is a prime. Take $F=K(\sqrt[4]{-q},\sqrt{-1})$. Then we proved that $X_{F\tilde{K}}=0$; see the paper (https://link.springer.com/article/10.100 …
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  • 1,053
14 votes
1 answer
1k views

How Dirichlet proved Dirichlet's unit theorem for general number fields?

For a general number field $K$, Dirichlet's unit theorem states that the unit group of the ring of integers of $K$ is a finitely generated group of rank $r_1+r_2-1$. It seems that standard algebraic n …
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  • 1,053
3 votes
1 answer
277 views

What's the class group of $\mathbb{Q}^{\mathrm{ab}}$?

If $K/\mathbb{Q}$ is an infinite algebraic extension, define as usual the class group $Cl_K$ by the direct limit via the natural (conorm) map $Cl_K := \lim\limits_{\rightarrow} Cl_F$, where $F$ runs o …
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  • 1,053
9 votes
1 answer
513 views

class number of prime degree field with prime conductor

Let $K$ be an finite abelian extension of $\mathbf{Q}$ conductor $p$, where $p$ is an odd prime. That is, $K \subset \mathbf{Q}(\mu_ p)$, the $p$-th cyclotomic field. Let $h_K$ be the class number of …
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  • 1,053
4 votes
0 answers
390 views

Is every Dedekind domain the integral closure of some principal ideal domain?

I mean that $B$ is a Dedekind domain with fraction field $L$, which is a finite separable extension of a field $K$ that is the fraction field of a PID $A$ such that $B$ is the integral closure of $A$ …
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