BOUNDS ON NON-GAUSSIANITY IN THE VARIANCE FROM SMALL-SCALE COSMIC MICROWAVE BACKGROUND OBSERVATIONS

We compare the latest results from CMB experiments at scales around l( e) similar to 150 over different parts of the sky to test the hypothes is that they are drawn from a Gaussian distribution, as is usually ass umed. Using both the diagonal and the full covariance chi(2) tests, we compare the data with different sets of strategies and find in all ca ses incompatibility with the Gaussian hypothesis above the 1 sigma lev el. We show how to include a generic non-Gaussian signal in the data a nalysis. Results from CMB observations can be made compatible with eac h other by assuming a non-Gaussian distribution for the signal, with a kurtosis at a level B-4 = [delta(T)(4)](c)/[delta(T)(2)](2) similar o r equal to 90. A possible interpretation of this result is that the in itial fluctuations at the surface of last scattering are strongly non- Gaussian. Another interpretation is that the systematic errors have be en underestimated in all experiments by a factor of 2. Other explanati ons include foreground contamination, non-linear effects or a combinat ion of these.