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

Anna Ijjas, Jean Luc Lehners, Paul J. Steinhardt

Research output: Contribution to journalArticle

33 Scopus citations

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 nonlinear 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 nonlinearity of the conversion process during which entropic perturbations are turned into adiabatic ones, resulting in a local non-Gaussianity parameter, fNL∼5.

Original languageEnglish (US)
Article number123520
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Volume89
Issue number12
DOIs
StatePublished - Jun 25 2014

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Physics and Astronomy (miscellaneous)

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