On the Galois structure of the square root of the codifferent

D. Burns

Displaying similar documents to “On the Galois structure of the square root of the codifferent”

Galois module structure of rings of integers

Martin J. Taylor (1980)

Annales de l'institut Fourier

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Let $E / F$ be a Galois extension of number fields with $Γ =$ Gal $(E / F)$ and with property that the divisors of $(E : F)$ are non-ramified in $E / Q$ . We denote the ring of integers of $E$ by $𝒪_{E}$ and we study $𝒪_{E}$ as a $Z Γ$ -module. In particular we show that the fourth power of the (locally free) class of $𝒪_{E}$ is the trivial class. To obtain this result we use Fröhlich’s description of class groups of modules and his representative for the class of $ℰ_{E}$ , together with new determinantal congruences for cyclic group rings and corresponding...

Factorisability and wildly ramified Galois extensions

David J. Burns (1991)

Annales de l'institut Fourier

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Let $L / K$ be an abelian extension of $p$ -adic fields, and let $𝒪$ denote the valuation ring of $K$ . We study ideals of the valuation ring of $L$ as integral representations of the Galois group $Gal (L / K)$ . Assuming $K$ is absolutely unramified we use techniques from the theory of factorisability to investigate which ideals are isomorphic to an $𝒪$ -order in the group algebra $K [Gal (l / K)]$ . We obtain several general and also explicit new results.

Relative Galois module structure of integers of abelian fields

Nigel P. Byott, Günter Lettl (1996)

Journal de théorie des nombres de Bordeaux

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Let $L / K$ be an extension of algebraic number fields, where $L$ is abelian over $ℚ$ . In this paper we give an explicit description of the associated order $𝒜_{L / K}$ of this extension when $K$ is a cyclotomic field, and prove that $o_{L}$ , the ring of integers of $L$ , is then isomorphic to $𝒜_{L / K}$ . This generalizes previous results of Leopoldt, Chan Lim and Bley. Furthermore we show that $𝒜_{L / K}$ is the maximal order if $L / K$ is a cyclic and totally wildly ramified extension which is linearly disjoint to $ℚ^{(m^{'})} / K$ , where $m^{'}$ is the conductor...

The cyclic subfield integer index

Bart de Smit (2000)

Journal de théorie des nombres de Bordeaux

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In this note we consider the index in the ring of integers of an abelian extension of a number field $K$ of the additive subgroup generated by integers which lie in subfields that are cyclic over $K$ . This index is finite, it only depends on the Galois group and the degree of $K$ , and we give an explicit combinatorial formula for it. When generalizing to more general Dedekind domains, a correction term can be needed if there is an inseparable extension of residue fields. We identify this correction...

CM-fields with all roots of unity

Kuniaki Horie (1990)

Compositio Mathematica

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Dihedral extensions of Q of degree 21 which contain non-Galois extensions with class number not divisible by l

Kiyoaki Iimura (1979)

Acta Arithmetica

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Galois module structure of the rings of integers in wildly ramified extensions

Stephen M. J. Wilson (1989)

Annales de l'institut Fourier

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The main results of this paper may be loosely stated as follows. Theorem.— Let $N$ and $N^{'}$ be sums of Galois algebras with group $Γ$ over algebraic number fields. Suppose that $N$ and $N^{'}$ have the same dimension $ℚ$ and that they are identical at their wildly ramified primes. Then (writing $𝒪_{N}$ for the maximal order in $N$ ) $𝒪_{N} \oplus 𝒪_{N} \oplus ℤ Γ ≅_{ℤ Γ} \oplus 𝒪_{N}^{'} \oplus 𝒪_{N^{'}} \oplus ℤ Γ .$

An analogue of Pfister's local-global principle in the burnside ring

Martin Epkenhans (1999)

Journal de théorie des nombres de Bordeaux

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Let $N / K$ be a Galois extension with Galois group $𝒢$ . We study the set $𝒯 (𝒢)$ of $ℤ$ -linear combinations of characters in the Burnside ring $ℬ (𝒢)$ which give rise to $ℤ$ -linear combinations of trace forms of subextensions of $N / K$ which are trivial in the Witt ring W $(K)$ of $K$ . In particular, we prove that the torsion subgroup of $ℬ (𝒢) / 𝒯 (𝒢)$ coincides with the kernel of the total signature homomorphism.

Galois structure of ideals in wildly ramified abelian $p$ -extensions of a $p$ -adic field, and some applications

Nigel P. Byott (1997)

Journal de théorie des nombres de Bordeaux

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Let $K$ be a finite extension of $ℚ_{p}$ with ramification index $e$ , and let $L / K$ be a finite abelian $p$ -extension with Galois group $Γ$ and ramification index $p^{n}$ . We give a criterion in terms of the ramification numbers $t_{i}$ for a fractional ideal $𝔓^{h}$ of the valuation ring $S$ of $L$ not to be free over its associated order $𝔄 (K Γ; 𝔓^{h})$ . In particular, if $t_{n} - [t_{n} / p] < p^{n - 1} e$ then the inverse different can be free over its associated order only when $t_{i} \equiv - 1$ (mod $p^{n}$ ) for all $i$ . We give three consequences of this. Firstly, if $𝔄 (K Γ; S)$ is a Hopf order and...