English

Patterns without a popular difference

Combinatorics 2021-08-02 v2 Number Theory

Abstract

Which finite sets PZrP \subseteq \mathbb{Z}^r with P3|P| \ge 3 have the following property: for every A[N]rA \subseteq [N]^r, there is some nonzero integer dd such that AA contains (αPo(1))Nr(\alpha^{|P|} - o(1))N^r translates of dP={dp:pP}d \cdot P = \{d p : p \in P\}, where α=A/Nr\alpha = |A|/N^r? Green showed that all 3-point PZP \subseteq \mathbb{Z} have the above property. Green and Tao showed that 4-point sets of the form P={a,a+b,a+c,a+b+c}ZP = \{a, a+b, a+c, a+b+c\} \subseteq \mathbb{Z} also have the property. We show that no other sets have the above property. Furthermore, for various PP, we provide new upper bounds on the number of translates of dPd \cdot P that one can guarantee to find.

Keywords

Cite

@article{arxiv.2004.07722,
  title  = {Patterns without a popular difference},
  author = {Ashwin Sah and Mehtaab Sawhney and Yufei Zhao},
  journal= {arXiv preprint arXiv:2004.07722},
  year   = {2021}
}

Comments

Computer code for appendix attached as ancillary files

R2 v1 2026-06-23T14:53:55.094Z