2014/12/31 by Elena Sellentin, Ruth Durrer · 40 citations
Physics and Astronomy · #Anisotropy #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Cosmic microwave background #Cosmic neutrino background #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Neutrino #Neutrino detector #Neutrino oscillation #Particle physics #Physics #astro-ph.CO #gr-qc #hep-ph
paper · pdf · doi:10.1103/physrevd.92.063012
published in Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields 92(6) (American Physical Society) · 10 pages 7 figures, version accepted for publication in PRD
arxiv created 2015/07/27 · openalex publication_date 2015/09/18 · arxiv updated 2015/09/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Three relativistic particles in addition to the photon are detected in the cosmic microwave background (CMB). In the standard model of cosmology, these are interpreted as the three neutrino species. However, at the time of CMB decoupling, neutrinos are not only relativistic but they are also free-streaming. Here we investigate whether the CMB is sensitive to this defining feature of neutrinos, or whether the CMB data allow us to replace neutrinos with a relativistic fluid. We show that free-streaming particles are preferred over a relativistic perfect fluid with \mathrm\ensuremathΔ\ensuremathχ2\ensuremath≃21. We then study the possibility to replace the neutrinos by a viscous fluid and find that also a relativistic viscous fluid with either the standard values ceff2=cvis2=1/3 or best-fit values for ceff2 and cvis2 has \mathrm\ensuremathΔ\ensuremathχ2\ensuremath≃20 and thus cannot provide a good fit to present CMB data either.