Sumsets of reciprocals in prime fields and multilinear Kloosterman sums
  We obtain new results on additive properties of the set $$ I^{-1}= \{x^{-1}: \quad x\in I\} $$ where $I$ is an arbitrary interval in the field of residue classes modulo a large prime $p$. We combine our results with multilinear exponential sum estimates and obtain new results on incomplete multilinear Kloosterman sums. 
J. Bourgain and M. Z. Garaev
math.NT