2011/06/03 by Mar Bastero-Gil, M. Bastero-Gil, Arjun Berera +3 · 127 citations
Engineering · Physics and Astronomy · #Cosmology and Gravitation Theories #Curvature #Dissipation #Dissipative system #Fluctuation spectrum #Galaxies: Formation, Evolution, Phenomena #Inflation (cosmology) #Inflaton #Shear (geology) #Space Technology and Applications #Spectral density #astro-ph.CO #hep-ph
paper · pdf · doi:10.1088/1475-7516/2011/07/030
published in Journal of Cosmology and Astroparticle Physics 2011(07), 030 (Institute of Physics) · 18 pages, 6 figures
arxiv created 2011/06/03 · openalex publication_date 2011/07/19 · arxiv updated 2015/05/28 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We compute the primordial curvature spectrum generated during warm inflation, including shear viscous effects. The primordial spectrum is dominated by the thermal fluctuations of the radiation bath, sourced by the dissipative term of the inflaton field. The dissipative coefficient Υ, computed from first principles in the close-to-equilibrium approximation, depends in general on the temperature T , and this dependence renders the system of the linear fluctuations coupled. Whenever the dissipative coefficient is larger than the Hubble expansion rate H , there is a growing mode in the fluctuations before horizon crossing. However, dissipation intrinsically means departures from equilibrium, and therefore the presence of a shear viscous pressure in the radiation fluid. This in turn acts as an extra friction term for the radiation fluctuations that tends to damp the growth of the perturbations. Independently of the T functional dependence of the dissipation and the shear viscosity, we find that when the shear viscous coefficient ζ s is larger than 3ρ r / H at horizon crossing, ρ r being the radiation energy density, the shear damping effect wins and there is no growing mode in the spectrum.