The 21cm radiation from minihalos as a probe of small primordial
  non-Gaussianity
  We present a new probe of primordial non-Gaussianity via the 21cm radiation
from minihalos at high redshifts. We calculate the fluctuations in the
brightness temperature (measured against the cosmic microwave background) of
the 21cm background from minihalos containing HI at redshift \sim 6-20, and
find a significant enhancement due to small non-Gaussianity with amplitude f_NL
\leq 1. This enhancement can be attributed to the nonlinear bias which is
strongly increased in the presence of non-Gaussianity. We show that our results
are robust against changes in the assumed mass function and some physical
aspects of minihalo formation, but are nevertheless sensitive to the presence
of strong radiation sources within or around the minihalos. Our findings are
relevant for constraining and searching for small primordial non-Gaussianity
with upcoming radio telescopes such as LOFAR and SKA.
