Sums of multiplicative characters with additive convolutions
  In the paper we obtain new estimates for binary and ternary sums of multiplicative characters with additive convolutions of characteristic functions of sets, having small additive doubling. In particular, we improve a result of M.-C. Chang. The proof uses Croot-Sisask almost periodicity lemma. 
Ilya D. Shkredov, Aleksei S. Volostnov
math.NT math.CO