Abstract
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, ${c}_{\mathrm{eff}}^{2}$, using the most recent CMB and large-scale structure data. Additionally, we report improved constraints to the CDRB viscosity parameter, ${c}_{\mathrm{vis}}^{2}$. 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 ${c}_{\mathrm{eff}}^{2}={0.30}_{\ensuremath{-}0.026}^{+0.027}$ and ${c}_{\mathrm{vis}}^{2}={0.44}_{\ensuremath{-}0.21}^{+0.27}$ (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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.