Multiple Methods for Estimating the Bispectrum of the Cosmic Microwave   Background with Application to the MAXIMA Data
  We describe different methods for estimating the bispectrum of Cosmic Microwave Background data. In particular we construct a minimum variance estimator for the flat-sky limit and compare results with previously-studied frequentist methods. Application to the MAXIMA dataset shows consistency with primordial Gaussianity. Weak quadratic non-Gaussianity is characterised by a tunable parameter $f_{NL}$, corresponding to non-Gaussianity at a level $\sim 10^{-5}f_{NL}$ (ratio of non-Gaussian to Gaussian terms), and we find limits of $|f_{NL}|<950$ for the minimum-variance estimator and $|f_{NL}|<1650$ for the usual frequentist estimator. These are the tightest limits on primordial non-Gaussianity which include the full effects of the radiation transfer function. 
M. G. Santos, A. Heavens, A. Balbi, J. Borrill, P. G. Ferreira, S.   Hanany, A. H. Jaffe, A. T. Lee, B. Rabii, P. L. Richard...