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 language | English (US) |
---|---|
Article number | 123520 |
Journal | Physical Review D - Particles, Fields, Gravitation and Cosmology |
Volume | 89 |
Issue number | 12 |
DOIs | |
State | Published - Jun 25 2014 |
Externally published | Yes |
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)