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arXiv 0709.0854math.NT
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轻度约束逼近的丢番图指数

Diophantine exponents for mildly restricted approximation

Yann Bugeaud, Simon Kristensen

摘要:

本文研究了丢番图指数μ_{n,l}$对整数1 \leq l <n和向量α \in \mathbb{R}^n的定义,令μ_{n,l}= \sup{μ\geq 0: 0 < ||x \cdot α|| < H(x)^{-μ} for infinitely many x \in C_{n,l} \cap \mathbb{Z}^n},其中\cdot是标量积,||. || 表示到最近整数的距离,C_{n,l}是由具有在第一个l坐标中获得的高度的所有矢量组成的广义圆锥。我们证明了指数取区间[l +1,\infty)中的所有值,并且几乎对所有α都取n值.我们计算了μ \geq n中向量集α的Hausdorff维数,其中μ_{n,l}(α)= μ.最后,设w_n表示去掉x的限制后的指数,我们证明了存在向量α使得递增序列μ_{n,1}(α)\leq. \leq μ_{n,n-1}(α)\leq w_n(α)可以任意选取。

英文摘要:

We are studying the Diophantine exponent μ_{n,l}$ defined for integers 1 \leq l < n and a vector α\in \mathbb{R}^n by letting μ_{n,l} = \sup{μ\geq 0: 0 < ||x \cdot α|| < H(x)^{-μ} for infinitely many x \in C_{n,l} \cap \mathbb{Z}^n}, where \cdot is the scalar product and || . || denotes the distance to the nearest integer and C_{n,l} is the generalised cone consisting of all vectors with the height attained among the first l coordinates. We show that the exponent takes all values in the interval [l+1, \infty), with the value n attained for almost all α. We calculate the Hausdorff dimension of the set of vectors αwith μ_{n,l} (α) = μfor μ\geq n. Finally, letting w_n denote the exponent obtained by removing the restrictions on x, we show that there are vectors αfor which the gaps in the increasing sequence μ_{n,1} (α) \leq ... \leq μ_{n,n-1} (α) \leq w_n (α) can be chosen to be arbitrary.

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