Sum–product theorems and exponential sum bounds in residue classes for general modulus

The purpose of this Note is to extend (in the appropriate formulation) the sum–product theorem in Zq=Z/qZ (established in [J. Bourgain, N. Katz, T. Tao, A sum–product estimate in finite fields and applications, GAFA 14 (2004) 27–57; J. Bourgain, A. Glibichuk, S. Konyagin, Estimate for the number of sums and products and for exponential sums in fields of prime order, J. London Math. Soc. 73 (2006) 380–398] for q prime, in [J. Bourgain, M. Chang, Exponential sum estimates over subgroups and almost subgroups of , where q is composite with few factors, GAFA 16 (2) (2006) 327–366] for q composite with few factors and in [J. Bourgain, A. Gamburd, P. Sarnak, Sieving and expanders, C. R. Acad. Sci. Paris, Ser. I 343 (3) (2006) 155–159] for q square free) to the case of arbitrary modulus. Consequences to exponential sum bounds (mod q) are given. To cite this article: J. Bourgain, C. R. Acad. Sci. Paris, Ser. I 344 (2007).

RésuméDans cette Note, nous généralisons (avec un énoncé approprié) le théorème somme–produit dans Zq=Z/qZ, où q est arbitraire (pour q premier, un tel résultat fût obtenu dans [J. Bourgain, N. Katz, T. Tao, A sum–product estimate in finite fields and applications, GAFA 14 (2004) 27–57 ; J. Bourgain, A. Glibichuk, S. Konyagin, Estimate for the number of sums and products and for exponential sums in fields of prime order, J. London Math. Soc. 73 (2006) 380–398], pour q un nombre composé avec un nombre de facteurs premiers borné dans [J. Bourgain, M. Chang, Exponential sum estimates over subgroups and almost subgroups of , where q is composite with few factors, GAFA 16 (2) (2006) 327–366], et pour q un produit simple dans [J. Bourgain, A. Gamburd, P. Sarnak, Sieving and expanders, C. R. Acad. Sci. Paris, Ser. I 343 (3) (2006) 155–159]. Nous en déduisons également des estimées sur certaines sommes exponentielles (mod q). Pour citer cet article : J. Bourgain, C. R. Acad. Sci. Paris, Ser. I 344 (2007).