arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2408.09301math.COmath.NT
收藏

紧交换群中缺失差集的集合研究

On sets with missing differences in compact abelian groups

Pablo Candela, Fernando Chamizo, Antonio Córdoba

AI总结:

本文将Motzkin缺失差问题推广到紧交换群,证明其等价于有限秩商群上的离散问题,并依据格秩判定最大密度避开集是否周期存在,推出至多三个缺失差时密度为有理数。

摘要:

Motzkin提出的一个被广泛研究的问题是:给定整数有限集合D,确定所谓D的Motzkin密度,即差集避开D的整数集合的上密度的上确界。我们研究该问题在紧交换群中的自然类比。利用遍历理论工具,这被证明等价于如下离散问题:给定格Λ⊂Z^r,令D为标准基在Z^r/Λ中的像,确定Z^r/Λ中D的Motzkin密度。我们特别研究周期性问题:在Z^r/Λ中是否存在具有最大密度的周期性D-避开集合?Greenfeld–Tao对周期性铺砌猜想的反例意味着答案可能是否定的。另一方面,我们证明在若干情形下答案为肯定,包括rank(Λ)=1的情形(其中给出了Motzkin密度的公式)、rank(Λ)=r−1的情形,因而也包括r≤3的情形。由此可知,对于至多三个缺失差,紧交换群中的Motzkin密度始终是有理数。

英文摘要:

A much-studied problem posed by Motzkin asks to determine, given a finite set $D$ of integers, the so-called Motzkin density for $D$, i.e., the supremum of upper densities of sets of integers whose difference set avoids $D$. We study the natural analogue of this problem in compact abelian groups. Using ergodic-theoretic tools, this is shown to be equivalent to the following discrete problem: given a lattice $Λ\subset \mathbb{Z}^r$, letting $D$ be the image in $\mathbb{Z}^r/Λ$ of the standard basis, determine the Motzkin density for $D$ in $\mathbb{Z}^r/Λ$. We study in particular the periodicity question: is there a periodic $D$-avoiding set of maximal density in $\mathbb{Z}^r/Λ$? The Greenfeld--Tao counterexample to the periodic tiling conjecture implies that the answer can be negative. On the other hand, we prove that the answer is positive in several cases, including the case rank$(Λ)=1$ (in which we give a formula for the Motzkin density), the case rank$(Λ)=r-1$, and hence also the case $r\leq 3$. It follows that, for up to three missing differences, the Motzkin density in a compact abelian group is always a rational number.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑