It has been pointed out by several groups that ekpyrotic and cyclic models generate significant non-gaussianity. In this paper, we present a physically intuitive, semi-analytic estimate of the bispectrum. We show that, in all such models, there is an intrinsic contribution to the non-gaussianity parameter f_{ NL} that is determined by the geometric mean of the equation of state w_{ ek} during the ekpyrotic phase and w_{ c} during the phase that curvature perturbations are generated and whose value is O(100) or more times the intrinsic value predicted by simple slow-roll inflationary models, f_{ NL}^{ intrinsic} = O(0.1). Other contributions to f_{ NL}, which we also estimate, can increase |f_{ NL}| but are unlikely to decrease it significantly, making non-gaussianity a useful test of these models. Furthermore, we discuss a predicted correlation between the non-gaussianity and scalar spectral index that sharpens the test.
Categories: hep-th astro-ph