Advanced Search

Nous étudions l'approximation simultanée de nombres complexes transcendants par des nombres algébriques de degré borné. Nous montrons que deux nombres qui ne sont pas simultanément bien approchables sont tous deux très bien approchables par des nombres algébriques de degré borné.

Let d be a positive integer and α a real algebraic number of degree d + 1. Set $\alpha ̲:=(\alpha ,\alpha ²,...,{\alpha }^d)$. It is well-known that $c\left(\alpha ̲\right):=limin{f}_{q\to \infty }{q}^{1/d}·\left|\right|q\alpha ̲\left|\right|>0$, where ||·|| denotes the distance to the nearest integer. Furthermore, $c\left(\alpha ̲\right)n^{-1/d}\le c\left(n\alpha ̲\right)\le nc\left(\alpha ̲\right)$ for any integer n ≥ 1. Our main result asserts that there exists a real number C, depending only on α, such that $c\left(n\alpha ̲\right)\le C{n}^{-1/d}$ for any integer n ≥ 1.

In 1955, Roth established that if $\xi$ is an irrational number such that there are a positive real number $\epsilon$ and infinitely many rational numbers $p/q$ with $q\ge 1$ and $|\xi -p/q|\<q^{-2-\epsilon }$, then $\xi$ is transcendental. A few years later, Cugiani obtained the same conclusion with $\epsilon$ replaced by a function $q\mapsto \epsilon \left(q\right)$ that decreases very slowly to zero, provided that the sequence of rational solutions to $|\xi -p/q|\<q^{-2-\epsilon \left(q\right)}$ is sufficiently dense, in a suitable sense. We give an alternative, and much simpler, proof of Cugiani’s Theorem and extend it to simultaneous...

We establish new combinatorial transcendence criteria for continued fraction expansions. Let $\alpha =[0;a_1,a_2,...]$ be an algebraic number of degree at least three. One of our criteria implies that the sequence of partial quotients ${\left(a_{\ell }\right)}_{\ell \ge 1}$ of $\alpha$ is not ‘too simple’ (in a suitable sense) and cannot be generated by a finite automaton.

Let ${\left(t_k\right)}_{k\ge 0}$ be the Thue–Morse sequence on $\{0,1\}$ defined by $t_0=0$, $t_{2k}=t_k$ and $t_{2k+1}=1-t_k$ for $k\ge 0$. Let $b\ge 2$ be an integer. We establish that the irrationality exponent of the Thue–Morse–Mahler number ${\sum }_{k\ge 0}{t}_k{b}^{-k}$ is equal to $2$.

For a positive integer $n$ and a real number $\xi$, let ${\lambda }_n\left(\xi \right)$ denote the supremum of the real numbers $\lambda$ such that there are arbitrarily large positive integers $q$ such that $\left|\right|q\xi \left|\right|,\left|\right|q{\xi }^2\left|\right|,...,\left|\right|q{\xi }^n\left|\right|$ are all less than $q^{-\lambda }$. Here, $\left|\right|·\left|\right|$ denotes the distance to the nearest integer. We study the set of values taken by the function ${\lambda }_n$ and, more generally, we are concerned with the joint spectrum of $({\lambda }_1,...,{\lambda }_n,...)$. We further address several open problems.

During the last decade, several quite unexpected applications of the Schmidt Subspace Theorem were found. We survey some of these, with a special emphasize on the consequences of quantitative statements of this theorem, in particular regarding transcendence questions.

The Littlewood conjecture in Diophantine approximation claims that $$\underset{q\ge 1}{inf}q·\parallel q\alpha \parallel ·\parallel q\beta \parallel =0$$ holds for all real numbers $\alpha$ and $\beta$, where $\parallel ·\parallel$ denotes the distance to the nearest integer. Its $p$-adic analogue, formulated by de Mathan and Teulié in 2004, asserts that $$\underset{q\ge 1}{inf}q·\parallel q\alpha \parallel ·{\left|q\right|}_p=0$$ holds for every real number $\alpha$ and every prime number $p$, where ${|·|}_p$ denotes the $p$-adic absolute value normalized by ${\left|p\right|}_p=p^{-1}$. We survey the known results on these conjectures and highlight recent developments.

Nous montrons que l’inégalité de Liouville-Baker-Feldman $|\alpha -y/x|{\gg }_{\mathrm{eff}}{x}^{\gamma -n}$ est une conséquence facile d’une minoration de formes linéaires en deux logarithmes.