### 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 |
---|---|

Article number | 024 |

Journal | Journal of Cosmology and Astroparticle Physics |

Issue number | 11 |

DOIs | |

Publication status | Published - 2007 Nov 1 |

Externally published | Yes |

### Fingerprint

### Keywords

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

### ASJC Scopus subject areas

- Physics and Astronomy(all)

### Cite this

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

**Non-Gaussianities from ekpyrotic collapse with multiple fields.** / Koyama, Kazuya; Mizuno, Shuntaro; Vernizzi, Filippo; Wands, David.

Research output: Contribution to journal › Article

*Journal of Cosmology and Astroparticle Physics*, no. 11, 024. https://doi.org/10.1088/1475-7516/2007/11/024

}

TY - JOUR

T1 - Non-Gaussianities from ekpyrotic collapse with multiple fields

AU - Koyama, Kazuya

AU - Mizuno, Shuntaro

AU - Vernizzi, Filippo

AU - Wands, David

PY - 2007/11/1

Y1 - 2007/11/1

N2 - 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, -Viexp(-ci 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 fNL = 5c j 2/12, where cj 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.

AB - 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, -Viexp(-ci 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 fNL = 5c j 2/12, where cj 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.

KW - Cosmological perturbation theory

KW - Cosmology with extra dimensions

KW - String theory and cosmology

UR - http://www.scopus.com/inward/record.url?scp=36749091266&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=36749091266&partnerID=8YFLogxK

U2 - 10.1088/1475-7516/2007/11/024

DO - 10.1088/1475-7516/2007/11/024

M3 - Article

AN - SCOPUS:36749091266

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 11

M1 - 024

ER -