Abstract. Let Fp be the field of residue classes modulo a prime number p and let A be a nonempty subset of Fp. In this paper we show that if |A| p 0.5 , then max{|A ± A|, |AA|} |A| 13/12 ;These results slightly improve the estimates of Bourgain-Garaev and Shen. Sum-product estimates on different sets are also considered.
IntroductionLet F p be the field of residue classes modulo a prime number p and let A, B be two nonempty subsets of F p . Define the sum set, difference set and product set of A and B respectively byFrom the work of Bourgain, Katz, Tao [4] and Bourgain, Glibichuk, Konyagin [3], it is known that if |A| p δ (see Section 2 for the definitions of , , , and ∼), where δ < 1, then one has the sum-product estimate max{|A + A|, |AA|} |A| 1+ǫ for some ǫ = ǫ(δ) > 0. These kinds of results have found many important applications in various areas of mathematics, and people want to know some quantitative relationships between δ and ǫ in certain ranges of |A|. For the case |A| p 0.5 , the pioneer work was due to Hart, Iosevich and Solymosi [12] via Kloosterman sums. See [6,8,18] for further improvements. Note also all lower bounds in [6,8,12,18]