### Abstract

We compute the non-Gaussianity of the curvature perturbation generated by ekpyrotic collapse with multiple fields. The transition from the multi-field scaling solution to a single-field dominated regime converts initial isocurvature field perturbations to an almost scale invariant comoving curvature perturbation. In the specific model of two fields, _{1} and _{2}, with exponential potentials, -V_{i}exp(-c_{i} _{i}), we calculate the bispectrum of the resulting curvature perturbation. We find that the non-Gaussianity is dominated by non-linear evolution on super-Hubble scales and hence is of the local form. The non-linear parameter of the curvature perturbation is given by f_{NL} = 5c _{j}
^{2}/12, where c_{j} is the exponent of the potential for the field which becomes subdominant at late times. Since c _{j}
^{2} must be large, in order to generate an almost scale invariant spectrum, the non-Gaussianity is inevitably large. Thus, the model is strongly constrained by observational bounds on the spectral index and non-Gaussianity.

Original language | English |
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Article number | 024 |

Journal | Journal of Cosmology and Astroparticle Physics |

Issue number | 11 |

DOIs | |

Publication status | Published - 2007 Nov 1 |

Externally published | Yes |

### Keywords

- Cosmological perturbation theory
- Cosmology with extra dimensions
- String theory and cosmology

### ASJC Scopus subject areas

- Physics and Astronomy(all)

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## Cite this

*Journal of Cosmology and Astroparticle Physics*, (11), [024]. https://doi.org/10.1088/1475-7516/2007/11/024