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arXiv · 0712.3779

Non-Gaussian Density Fluctuations from Entropically Generated Curvature Perturbations in Ekpyrotic Models

Jean-Luc Lehners·Paul J. Steinhardt
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Abstract

We analyze the non-gaussian density perturbations generated in ekpyrotic/cyclic models based on heterotic M-theory. In this picture, two scalar fields produce nearly scale-invariant entropic perturbations during an ekpyrotic phase that are converted into curvature modes {\it after the ekpyrotic phase is complete} and just before the big bang. Both intrinsic non-linearity in the entropy perturbation and the conversion process contribute to non-gaussianity. The range of the non-gaussianity parameter $f_{NL}$ depends on how gradual the conversion process is and the steepness of the scalar field potential during the ekpyrotic phase. Although a wider range is possible, in principle, natural values of the ekpyrotic parameters combined with a gradual conversion process lead to values of $-60 \lesssim f_{NL} \lesssim +80$, typically much greater than slow-roll inflation but within the current observational bounds.

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Jean-Luc Lehners, Paul J. Steinhardt. 2009-06-02. Non-Gaussian Density Fluctuations from Entropically Generated Curvature Perturbations in Ekpyrotic Models. https://doi.org/10.1103/physrevd.77.063533%2010.1103%2Fphysrevd.79.129903

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