THE ANGULAR BISPECTRUM OF THE COSMIC MICROWAVE BACKGROUND

COBE has provided us with a whole-sky map of the CBR anisotropies. How ever, even if the noise level is negligible when the 4 year COBE data are available, the cosmic variance will prevent us from obtaining info rmation about the Gaussian nature of the primordial fluctuations. This important issue is addressed here by studying the angular bispectrum of the cosmic microwave background anisotropies. A general form of the angular bispectrum is given and the cosmic variance of the angular bi spectrum for Gaussian fluctuations is calculated. The advantage of usi ng the angular bispectrum is that one can choose to use the multipole moments which minimize the cosmic variance term. The non-Gaussian sign als in most physically motivated non-Gaussian models are small compare d with cosmic variance. Unless the amplitudes are large, the non-Gauss ian signals are only detectable in the COBE data in those models where the angular bispectrum is flat or increases with increasing multipole moment.