A New Window on Primordial non-Gaussianity
  We know very little about primordial curvature perturbations on scales
smaller than about a Mpc. Measurements of the mu-type distortion of the CMB
spectrum provide the unique opportunity to probe these scales over the
unexplored range from 50 to 10^4 Mpc^-1. This is a very clean probe, in that it
relies only on well-understood linear evolution. We point out that correlations
between mu-distortion and temperature anisotropies can be used to test
Gaussianity at these very small scales. In particular the mu-T cross
correlation is proportional to the very squeezed limit of the primordial
bispectrum and hence measures fNL^loc, while mu-mu is proportional to the
primordial trispectrum and measures tauNL. We present a Fisher matrix forecast
of the observational constraints.
