  Light scalars may be ubiquitous in nature, and their quantum fluctuations can
produce large non-Gaussianity in the cosmic microwave background temperature
anisotropy. The non-Gaussianity may be accompanied with a small admixture of
isocurvature perturbations, which often have correlations with the curvature
perturbations. We present a general method to calculate the non-Gaussianity in
the adiabatic and isocurvature perturbations with and without correlations, and
see how it works in several explicit examples. We also show that they leave
distinct signatures on the bispectrum of the cosmic microwave background
temperature fluctuations.
