2016/03/31 by Aaron M. Levy, Gustavo J. Turiaci, Gustavo Turiaci · 3 citations
Mathematics · Physics and Astronomy · #Adiabatic invariant #Adiabatic process #Adrenomedullin #Advanced Differential Geometry Research #Black Holes and Theoretical Physics #Classical mechanics #Cosmology #Cosmology and Gravitation Theories #Coupling (piping) #Curvature #Dark energy #Ekpyrotic universe #Invariant (physics) #Materials science #Mathematics #Physics #Quantum mechanics #Scalar (mathematics) #Scalar field #Scale invariance #astro-ph.CO #gr-qc #hep-th
paper · pdf · doi:10.1103/physrevd.94.083514
published in Physical review. D/Physical review. D. 94(8) (American Physical Society) · 10 pages, 5 figures. References added
arxiv created 2016/04/27 · openalex publication_date 2016/10/10 · arxiv updated 2016/10/19 · openalex created_date 2020/07/02 · openalex updated_date 2026/08/05
We propose a mechanism to generate a nearly scale-invariant spectrum of adiabatic scalar perturbations about a stable, ekpyrotic background. The key ingredient is a coupling between a single ekpyrotic field and a perfect fluid of ultrarelativistic matter. This coupling introduces a friction term into the equation of motion for the field, opposing the Hubble antifriction, which can be chosen such that an exactly scale-invariant (or nearly scale-invariant) spectrum of adiabatic density perturbations is continuously produced throughout the ekpyrotic phase. This mechanism eliminates the need for a second (entropic) scalar field and hence any need for introducing a second phase for converting entropic into curvature fluctuations. It also reduces the constraints on the equation of state during the ekpyrotic phase and, thereby, the need for parametric fine-tuning.