Optimal constraint on g_NL from CMB
  An optimal method to constrain the non-linearity parameter g_NL of the
local-type non-Gaussianity from CMB data is proposed. Our optimal estimator for
g_NL is separable and can be efficiently computed in real space. Combining the
exact filtering of CMB maps with the full covariance matrix, our method allows
us to extract cosmological information from observed data as much as possible
and obtain a tighter constraint on g_NL than previous studies. Applying our
method to the WMAP 9-year data, we obtain the constraint g_NL = (-3.3 +- 2.2)
10^5, which is a few times tighter than previous ones. We also make a forecast
for PLANCK data by using the Fisher matrix analysis.
