The Case for Dark Radiation

Original · EN

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 for an extra relativistic component with =4.08₋₀.₆₈⁺⁰.⁷¹ at 95% c.l.. Performing an analysis on Dark Radiation sound speed c eff and viscosity c vis parameters, we found =0.312±0.026 and =0.29₋₀.₁₆⁺⁰.²¹ at 95% c.l., consistent with the expectations of a relativistic free streaming component (==1/3). Assuming the presence of 3 relativistic neutrinos we constrain the extra relativistic component with =1.10₋₀.₇₂⁺⁰.⁷⁹ and =0.24₋₀.₁₃⁺⁰.⁰⁸ at 95% c.l. while results as unconstrained. Assuming a massive neutrino component we obtain further indications for Dark Radiation with =1.12₋₀.₇₄⁺⁰.⁸⁶ at 95% c.l..