A Bound Concerning Primordial Non-Gaussianity
  Seery and Lidsey have calculated the three-point correlator of the light scalar fields, a few Hubble times after horizon exit during inflation. Lyth and Rodriguez have calculated the contribution of this correlator to the three-point correlator of the primordial curvature perturbation. We calculate an upper bound on that contribution, showing that it is too small ever to be observable. 
David H. Lyth and Ignacio Zaballa (Department of Physics, Lancaster   University, UK)