Dans cette note nous décrivons différentes méthodes utilisées en pratique pour calculer le nombre de classes d'un corps quadratique imaginaire ou réel ainsi que pour calculer le régulateur d'un corps quadratique réel. En particulier nous décrivons l'infrastructure de Shanks ainsi que la méthode sous-exponentielle de McCurley.

L’article comporte une méthode de calcul de fonctions de Belyi “optimales”, associées à des dessins plans. Cette étude conduit à s’interroger sur la possibilité de définir une fonction de Belyi sur le corps des modules du dessin. Pour les arbres par exemple, nous montrons que c’est toujours le cas. La preuve donne une méthode pour spécifier une telle fonction. Nous donnons ensuite un exemple de dessin qui n’admet pas de fonction de Belyi sur son corps des modules. Enfin, nous étudions la question...

It is a classical problem in algebraic number theory to decide if a number field is monogeneous, that is if it admits power integral bases. It is especially interesting to consider this question in an infinite parametric family of number fields. In this paper we consider the infinite parametric family of simplest quartic fields $K$ generated by a root $\xi$ of the polynomial $P_t\left(x\right)=x^4-t{x}^3-6x^2+tx+1$, assuming that $t>0$, $t\ne 3$ and $t^2+16$ has no odd square factors. In addition to generators of power integral bases we also calculate the minimal...

Let $R$ be a non-maximal order in a finite algebraic number field with integral closure $\overline{R}$. Although $R$ is not a unique factorization domain, we obtain a positive integer $N$ and a family $𝒬$ (called a Cale basis) of primary irreducible elements of $R$ such that $x^N$ has a unique factorization into elements of $𝒬$ for each $x\in R$ coprime with the conductor of $R$. Moreover, this property holds for each nonzero $x\in R$ when the natural map $\mathrm{Spec}\left(\overline{R}\right)\to \mathrm{Spec}\left(R\right)$ is bijective. This last condition is actually equivalent to several properties linked...

If $K/k$ is a finite Galois extension of number fields with Galois group $G$, then the kernel of the capitulation map $C{l}_k\to C{l}_K$ of ideal class groups is isomorphic to the kernel $X\left(H\right)$ of the transfer map $H/H^{\text{'}}\to A,$ where $H=\text{Gal}(\tilde{K}/k),A=\text{Gal}(\tilde{K}/K)$ and $\tilde{K}$ is the Hilbert class field of $K$. H. Suzuki proved that when $G$ is abelian, $\left|G\right|$ divides $\left|X\right(H\left)\right|$. We call a finite abelian group $X$ a transfer kernel for $G$ if $X\cong X\left(H\right)$ for some group extension $A\hookrightarrow H\twoheadrightarrow G$. After characterizing transfer kernels in terms of integral representations of $G$, we show that $X$ is a transfer kernel for...

Let $K=k\left(\sqrt{-p\epsilon \sqrt{l}}\right)$ with $k=\mathbb{Q}\left(\sqrt{l}\right)$ where $l$ is a prime number such that $l=2$ or $l\equiv 5mod8$, $\epsilon$ the fundamental unit of $k$, $p$ a prime number such that $p\equiv 1mod4$ and ${\left(\frac{p}{l}\right)}_4=-1$, $K_2^{\left(1\right)}$ the Hilbert $2$-class field of $K$, $K_2^{\left(2\right)}$ the Hilbert $2$-class field of $K_2^{\left(1\right)}$ and $G=Gal(K_2^{\left(2\right)}/K)$ the Galois group of $K_2^{\left(2\right)}/K$. According to E. Brown and C. J. Parry [7] and [8], $C_{2,K}$, the Sylow $2$-subgroup of the ideal class group of $K$, is isomorphic to $\mathbb{Z}/2\mathbb{Z}\times \mathbb{Z}/2\mathbb{Z}$, consequently $K_2^{\left(1\right)}/K$ contains three extensions $F_i/K$$...$

Soient $\mathbf{K}=\mathbf{Q}\left(\sqrt{-pq(2+\sqrt{2})}\right)$ où $p$ et $q$ deux nombres premiers différents tels que $p\equiv q\equiv \pm 5mod8$, ${\mathbf{K}}_2^{\left(1\right)}$ le $2$-corps de classes de Hilbert de $\mathbf{K}$, ${\mathbf{K}}_2^{\left(2\right)}$ le $2$-corps de classes de Hilbert de ${\mathbf{K}}_2^{\left(1\right)}$ et $G$ le groupe de Galois de ${\mathbf{K}}_2^{\left(2\right)}/K$. D’après [4], la $2$-partie $C_{2,\mathbf{K}}$ du groupe de classes de $\mathbf{K}$ est de type $(2,2)$, par suite ${\mathbf{K}}_2^{\left(1\right)}$ contient trois extensions ${\mathbf{F}}_i/\mathbf{K}$ ; $i=1,2,3$. Dans ce papier, on s’interesse au problème de capitulation des $2$-classes d’idéaux de $\mathbf{K}$ dans ${\mathbf{F}}_i$$...$

Let $p$ be a prime number and $F$ be a number field. Since Iwasawa’s works, the behaviour of the $p$-part of the ideal class group in the ${\mathbb{Z}}_p$-extensions of $F$ has been well understood. Moreover, M. Grandet and J.-F. Jaulent gave a precise result about its abelian $p$-group structure.On the other hand, the ideal class group of a number field may be identified with the torsion part of the $K_0$ of its ring of integers. The even $K$-groups of rings of integers appear as higher versions of the class group. Many authors...