General mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models
- Max-Planck-Inst. for Gravitational Physics, Potsdam (Germany); Rutgers Univ., New Brunswick, NJ (United States)
- Max-Planck-Inst. for Gravitational Physics, Potsdam (Germany)
- Princeton Univ., NJ (United States)
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. Finally, 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 fNL~5.
- Research Organization:
- Princeton Univ., NJ (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP); European Research Council (ERC)
- Grant/Contract Number:
- SC0007968; FG02-91ER40671; 256994
- OSTI ID:
- 1600652
- Journal Information:
- Physical Review. D, Particles, Fields, Gravitation and Cosmology, Vol. 89, Issue 12; ISSN 1550-7998
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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