Cosmology on Ultralarge Scales with Intensity Mapping of the Neutral
  Hydrogen 21 cm Emission: Limits on Primordial Non-Gaussianity
  The large-scale structure of the Universe supplies crucial information about
the physical processes at play at early times. Unresolved maps of the intensity
of 21 cm emission from neutral hydrogen HI at redshifts z~1-5 are the best hope
of accessing the ultralarge-scale information, directly related to the early
Universe. A purpose-built HI intensity experiment may be used to detect the
large scale effects of primordial non-Gaussianity, placing stringent bounds on
different models of inflation. We argue that it may be possible to place tight
constraints on the non-Gaussianity parameter f_NL, with an error close to ~1.
