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  General mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models

Ijjas, A., Lehners, J.-L., & Steinhardt, P. J. (2014). General mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models. Physical Review D, 89: 123520. doi:10.1103/PhysRevD.89.123520.

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Other : A general mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models

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 Creators:
Ijjas, Anna1, Author              
Lehners, Jean-Luc2, Author              
Steinhardt, Paul J., Author
Affiliations:
1Lise Meitner Excellence Group: Gravitational Theory and Cosmology, AEI-Hannover, MPI for Gravitational Physics, Max Planck Society, ou_3235822              
2Theoretical Cosmology, AEI-Golm, MPI for Gravitational Physics, Max Planck Society, ou_1753351              

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Free keywords: Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO,High Energy Physics - Theory, hep-th
 Abstract: We explore a new type of entropic mechanism for generating density perturbations in a contracting phase in which there are two scalar fields, but only one has a steep negative potential. This first field dominates the energy density and is the source of the ekpyrotic equation of state. The second field has a negligible potential, but its kinetic energy density is coupled to the first field with a non-linear sigma-model type interaction. We show that for any ekpyrotic equation of state it is possible to choose the potential and the kinetic coupling such that exactly scale-invariant (or nearly scale-invariant) entropy perturbations are produced. The corresponding background solutions are stable, and the bispectrum of the entropy perturbations vanishes as no non-Gaussianity is produced during the ekpyrotic phase. Hence, the only contribution to non-Gaussianity comes from the non-linearity of the conversion process during which entropic perturbations are turned into adiabatic ones, resulting in a local non-Gaussianity parameter $f_{NL} \sim 5$.

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 Dates: 2014-04-042014-06-052014
 Publication Status: Published in print
 Pages: 8 pages, 1 figure, accepted for publication in PRD
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: arXiv: 1404.1265
DOI: 10.1103/PhysRevD.89.123520
 Degree: -

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Title: Physical Review D
  Other : Phys. Rev. D.
Source Genre: Journal
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Publ. Info: Lancaster, Pa. : American Physical Society
Pages: - Volume / Issue: 89 Sequence Number: 123520 Start / End Page: - Identifier: ISSN: 0556-2821
CoNE: https://pure.mpg.de/cone/journals/resource/111088197762258