2013/10/31 by Angelika Fertig, Jean-Luc Lehners, Enno Mallwitz · 1 citation
Mathematics · Physics and Astronomy · #Anisotropy #Bispectrum #Classical mechanics #Cosmic microwave background #Cosmology and Gravitation Theories #Curvature #De Sitter universe #Ekpyrotic universe #Galaxies: Formation, Evolution, Phenomena #Geometry #Mathematics #Non-Gaussianity #Physics #Quantum mechanics #Scalar field #Solar and Space Plasma Dynamics #Spectral density #Statistical physics #Universe #astro-ph.CO #hep-th
paper · pdf · doi:10.1103/physrevd.89.103537
published as Phys. Rev. D 89, 103537 (2014) · 5 pages, v2: references added
arxiv created 2013/11/06 · openalex publication_date 2014/05/28 · arxiv updated 2014/06/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 nontrivial 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 nonlinearity 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 that the ekpyrotic phase does not generate significant primordial gravitational waves. Thus the present model provides a perfect match to current data from the PLANCK satellite.