COSMIC VARIANCE OF THE 3-POINT CORRELATION-FUNCTION OF THE COSMIC MICROWAVE BACKGROUND

The fluctuations in the cosmic microwave background radiation may contain deviations from Gaussian statistics which would be reflected in a nonzero value of the three-point correlation function of DELTAT. However, any potential observation of the three-point function is limited by cosmic variance, even if a whole-sky map of DELTAT is available. Here I derive a general formula for the cosmic variance of the three-point function in terms of integrals over the two-point function. This formula can be applied to any cosmological model and to any experimental measurement strategy. It gives a fundamental lower limit on the magnitude of a measurable three-point correlation function, and hence on the measurable amount of skewness in the distribution of DELTAT.