Abstract
Combined analyses of recent cosmological data are showing interesting hints for the presence of an extra relativistic component, coined dark radiation. Here, we perform a new search for dark radiation, parametrizing it with an effective number of relativistic degrees of freedom parameter, . We show that the cosmological data we considered are clearly suggesting the presence of an extra relativistic component with at 95% C.L.. Performing an analysis on dark radiation sound speed and viscosity parameters, we found and at 95% C.L., consistent with the expectations of a relativistic free streaming component (). Assuming the presence of 3 relativistic neutrinos, we constrain the extra relativistic component with and at 95% C.L. while results as unconstrained. Assuming a massive neutrino component, we obtain further indications for dark radiation with at 95% C.L..
- Received 16 September 2011
DOI:https://doi.org/10.1103/PhysRevD.84.123008
© 2011 American Physical Society