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 data set shows consistency with primordial Gaussianity. Weak quadratic non-Gaussianity is characterized by a tunable parameter f (NL) , corresponding to non-Gaussianity at a level of similar to10(-5) f (NL) (the ratio of non-Gaussian to Gaussian terms), and we find limits of f (NL) = 1500 +/- 950 for the minimum-variance estimator and f (NL) = 2700 +/- 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.