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|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, f(NL) similar to 5.|
|Electronic Publication Date:||25-Jun-2014|
|Citation:||Ijjas, Anna, Lehners, Jean-Luc, Steinhardt, Paul J. (2014). General mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models. PHYSICAL REVIEW D, 89, doi:10.1103/PhysRevD.89.123520|
|Type of Material:||Journal Article|
|Journal/Proceeding Title:||PHYSICAL REVIEW D|
|Version:||Final published version. Article is made available in OAR by the publisher's permission or policy.|
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