Maria Archidiacono, Erminia Calabrese, Alessandro Melchiorri
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, $\neff$. We show
that the cosmological data we considered are clearly suggesting the presence
for an extra relativistic component with $\neff=4.08_{-0.68}^{+0.71}$ at 95%
c.l.. Performing an analysis on Dark Radiation sound speed $c_{\rm eff}$ and
viscosity $c_{\rm vis}$ parameters, we found $\ceff=0.312\pm0.026$ and
$\cvis=0.29_{-0.16}^{+0.21}$ at 95% c.l., consistent with the expectations of a
relativistic free streaming component ($\ceff=\cvis$=1/3). Assuming the
presence of 3 relativistic neutrinos we constrain the extra relativistic
component with $\nnus=1.10_{-0.72}^{+0.79}$ and $\ceff=0.24_{-0.13}^{+0.08}$ at
95% c.l. while $\cvis$ results as unconstrained. Assuming a massive neutrino
component we obtain further indications for Dark Radiation with
$\nnus=1.12_{-0.74}^{+0.86}$ at 95% c.l. .
View original:
http://arxiv.org/abs/1109.2767
No comments:
Post a Comment