Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2008-04-08
Phys.Rev.D78:023506,2008; Erratum-ibid.D79:129902,2009
Physics
High Energy Physics
High Energy Physics - Theory
10 pages, 4 figures. Sign error corrected and results generalized, conclusions unchanged
Scientific paper
10.1103/PhysRevD.78.023506
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.
Lehners Jean-Luc
Steinhardt Paul J.
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