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We give a simple proof of the Siegel-Tatuzawa theorem according to which the residues at s = 1 of the Dedekind zeta functions of quadratic number fields are effectively not too small, with at most one exceptional quadratic field. We then give a simple proof of the Brauer-Siegel theorem for normal number fields which gives the asymptotics for the logarithm of the product of the class number and the regulator of number fields.

We prove that if χ is a real non-principal Dirichlet character for which L(1,χ) ≤ 1- log2, then Chowla's hypothesis is not satisfied and we cannot use Chowla's method for proving that L(s,χ) > 0 for s > 0.

Let ε be an algebraic unit for which the rank of the group of units of the order ℤ[ε] is equal to 1. Assume that ε is not a complex root of unity. It is natural to wonder whether ε is a fundamental unit of this order. It turns out that the answer is in general yes, and that a fundamental unit of this order can be explicitly given (as an explicit polynomial in ε) in the rare cases when the answer is no. This paper is a self-contained exposition of the solution to this problem, solution which was...

Let ε be a quartic algebraic unit. We give necessary and sufficient conditions for (i) the quartic number field K = ℚ(ε) to contain an imaginary quadratic subfield, and (ii) for the ring of algebraic integers of K to be equal to ℤ[ε]. We also prove that the class number of such K's goes to infinity effectively with the discriminant of K.

Let $\epsilon$ be an algebraic unit of the degree $n\ge 3$. Assume that the extension $\mathbb{Q}\left(\epsilon \right)/\mathbb{Q}$ is Galois. We would like to determine when the order $\mathbb{Z}\left[\epsilon \right]$ of $\mathbb{Q}\left(\epsilon \right)$ is $\mathrm{Gal}\left(\mathbb{Q}\right(\epsilon )/\mathbb{Q})$-invariant, i.e. when the $n$ complex conjugates ${\epsilon }_1,\cdots ,{\epsilon }_n$ of $\epsilon$ are in $\mathbb{Z}\left[\epsilon \right]$, which amounts to asking that $\mathbb{Z}[{\epsilon }_1,\cdots ,{\epsilon }_n]=\mathbb{Z}\left[\epsilon \right]$, i.e., that these two orders of $\mathbb{Q}\left(\epsilon \right)$ have the same discriminant. This problem has been solved only for $n=3$ by using an explicit formula for the discriminant of the order $\mathbb{Z}[{\epsilon }_1,{\epsilon }_2,{\epsilon }_3]$. However, there is no known similar formula for $n>3$. In the present paper, we put forward and motivate three...

Let ϵ be a totally real cubic algebraic unit. Assume that the cubic number field ℚ(ϵ) is Galois. Let ϵ, ϵ' and ϵ'' be the three real conjugates of ϵ. We tackle the problem of whether {ϵ,ϵ'} is a system of fundamental units of the cubic order ℤ[ϵ,ϵ',ϵ'']. Given two units of a totally real cubic order, we explain how one can prove that they form a system of fundamental units of this order. Several explicit families of totally real cubic orders defined by parametrized families of cubic polynomials...