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A NEW SUM–PRODUCT ESTIMATE IN PRIME FIELDS

Published online by Cambridge University Press:  24 May 2019

CHANGHAO CHEN
Affiliation:
Department of Pure Mathematics, University of New South Wales, Sydney, NSW 2052, Australia email changhao.chen@unsw.edu.au
BRYCE KERR*
Affiliation:
Department of Pure Mathematics, University of New South Wales, Sydney, NSW 2052, Australia email bryce.kerr@unsw.edu.au
ALI MOHAMMADI
Affiliation:
School of Mathematics and Statistics, University of Sydney, NSW 2006, Australia email alim@maths.usyd.edu.au

Abstract

We obtain a new sum–product estimate in prime fields for sets of large cardinality. In particular, we show that if $A\subseteq \mathbb{F}_{p}$ satisfies $|A|\leq p^{64/117}$ then $\max \{|A\pm A|,|AA|\}\gtrsim |A|^{39/32}.$ Our argument builds on and improves some recent results of Shakan and Shkredov [‘Breaking the 6/5 threshold for sums and products modulo a prime’, Preprint, 2018, arXiv:1806.07091v1] which use the eigenvalue method to reduce to estimating a fourth moment energy and the additive energy $E^{+}(P)$ of some subset $P\subseteq A+A$. Our main novelty comes from reducing the estimation of $E^{+}(P)$ to a point–plane incidence bound of Rudnev [‘On the number of incidences between points and planes in three dimensions’, Combinatorica 38(1) (2017), 219–254] rather than a point–line incidence bound used by Shakan and Shkredov.

Type
Research Article
Copyright
© 2019 Australian Mathematical Publishing Association Inc. 

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Footnotes

The first and second author were supported by ARC Grant DP170100786.

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