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Journal Article

Ekpyrotic Perturbations With Small Non-Gaussian Corrections


Fertig,  Angelika
AEI-Golm, MPI for Gravitational Physics, Max Planck Society;


Lehners,  Jean-Luc
String Cosmology, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;

Mallwitz,  Enno
AEI-Golm, MPI for Gravitational Physics, Max Planck Society;

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Fertig, A., Lehners, J.-L., & Mallwitz, E. (2014). Ekpyrotic Perturbations With Small Non-Gaussian Corrections. Physical Review D, 89: 103537. doi:10.1103/PhysRevD.89.103537.

Cite as: http://hdl.handle.net/11858/00-001M-0000-001A-0E49-5
The entropic mechanism for producing nearly scale-invariant density perturbations in a contracting ekpyrotic universe relies on having an unstable scalar potential. Here we develop a variant of this mechanism (recently proposed by Qiu, Gao and Saridakis, and by Li), in which there exists a non-trivial coupling between adiabatic and entropic fields, and where an unstable potential is not required. In the model nearly scale-invariant entropy perturbations are generated first. Remarkably, we find that the bispectrum of these perturbations vanishes, with the values of the non-Gaussianity parameters of local, equilateral and orthogonal type all exactly zero. Subsequently, the entropy perturbations can be converted into curvature perturbations by a variety of mechanisms. The bispectrum of the curvature perturbations depends on the non-linearity of the conversion process and is thus more model-dependent - however, for an efficient conversion process the final bispectrum remains small. The only distinguishing feature compared to single-field slow-roll inflationary models is an absence of primordial gravitational waves. Thus the present model provides a perfect match to current data from the PLANCK satellite.