2011/05/31 by Tristan L. Smith, Sudeep Das, Oliver Zahn +1 · 59 citations
Physics and Astronomy · #Astrophysics #Astrophysics and Cosmic Phenomena #COSMIC cancer database #Cosmic background radiation #Cosmic microwave background #Cosmology #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Dark energy #Dark radiation #Lambda-CDM model #Neutrino #Particle physics #Physics #Planck #Quantum mechanics #Standard Model (mathematical formulation) #astro-ph.CO
paper · pdf · doi:10.1103/physrevd.85.023001
published in Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields 85(2) (American Physical Society) · 6 pages, 3 figures, comments welcome; v2: updated with SPT data, corrected minor typos; v3: version accepted for publication in PRD
arxiv created 2012/01/02 · openalex publication_date 2012/01/06 · arxiv updated 2013/05/29 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Observations of the CMB and large-scale structure provide a unique opportunity to explore the fundamental properties of the constituents that compose the cosmic dark radiation background (CDRB), of which the three standard neutrinos are thought to be the dominant component. We report on the first constraint to the CDRB rest-frame sound speed, ceff2, using the most recent CMB and large-scale structure data. Additionally, we report improved constraints to the CDRB viscosity parameter, cvis2. For a noninteracting species, these parameters both equal 1/3. Using current data we find that a standard CDRB, composed entirely of three noninteracting neutrino species, is ruled out at the 99% confidence level (C.L.) with ceff2=0.30_\ensuremath-0.026+0.027 and cvis2=0.44_\ensuremath-0.21+0.27 (95% C.L.). We also discuss how constraints to these parameters from current and future observations (such as the Planck satellite) allow us to explore the fundamental properties of any anomalous radiative energy density beyond the standard three neutrinos.