English

Stronger sum-product inequalities for small sets

Combinatorics 2018-09-27 v4 Number Theory

Abstract

Let FF be a field and a finite AFA\subset F be sufficiently small in terms of the characteristic pp of FF if p>0p>0. We strengthen the "threshold" sum-product inequality AA3A±A2A6,        \mboxhence        AA+A+AA1+15,|AA|^3 |A\pm A|^2 \gg |A|^6\,,\;\;\;\;\mbox{hence} \;\; \;\;|AA|+|A+A|\gg |A|^{1+\frac{1}{5}}, due to Roche-Newton, Rudnev and Shkredov, to AA5A±A4A11o(1),        \mboxhence        AA+A±AA1+29o(1),|AA|^5 |A\pm A|^4 \gg |A|^{11-o(1)}\,,\;\;\;\;\mbox{hence} \;\; \;\;|AA|+|A\pm A|\gg |A|^{1+\frac{2}{9}-o(1)}, as well as AA36AA24A73o(1). |AA|^{36}|A-A|^{24} \gg |A|^{73-o(1)}. The latter inequality is "threshold-breaking", for it shows for ϵ>0\epsilon>0, one has AAA1+ϵ            AAA32+c(ϵ),|AA| \le |A|^{1+\epsilon}\;\;\;\Rightarrow\;\;\; |A-A|\gg |A|^{\frac{3}{2}+c(\epsilon)}, with c(ϵ)>0c(\epsilon)>0 if ϵ\epsilon is sufficiently small. This implies that regardless of ϵ\epsilon, AAAAA32+156o(1).|AA-AA|\gg |A|^{\frac{3}{2}+\frac{1}{56}-o(1)}\,.

Keywords

Cite

@article{arxiv.1808.08465,
  title  = {Stronger sum-product inequalities for small sets},
  author = {Misha Rudnev and George Shakan and Ilya Shkredov},
  journal= {arXiv preprint arXiv:1808.08465},
  year   = {2018}
}

Comments

v2: Improved sum-product bound to match difference-product bound

R2 v1 2026-06-23T03:43:49.580Z