Non-Gaussian bounds in the variance from small scale CMB observations

Abstract

We compare the latest results from CMB experiments at scales around $l_e\sim 150$ over different parts of the sky to test the hypothesis that they are drawn from a Gaussian distribution, as is usually assumed. Using both the diagonal and the full covariance ${\chi }^2$ test, we compare the data with different sets of strategies and find in all cases incompatibility with the Gaussian hypothesis above the one-sigma level. We next show how to include a generic non-Gaussian signal in the data analysis. Results from CMB observations can be made compatible with each other by assuming a non-Gaussian distribution for the signal, with a kurtosis at a level $B_4=<{\delta }_T^4{>}_c/{<{\delta }_T^2{>}_c}^2\simeq 90$. A possible interpretation for this result is that the initial fluctuations at the surface of last scattering are strongly non-Gaussian. Another interpretation is that the systematic errors have been understimated in all observations by a factor of two. Other explanations include foreground contamination, non-linear effects or a combination of them.

5 pages, 1 figure. Revised to match published version: MNRAS Letters 1998, 295, 35

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