Right-Handed Neutrinos as the Dark Radiation: Status and Forecasts for
  the LHC
  Precision data from cosmology (probing the CMB decoupling epoch) and
light-element abundances (probing the BBN epoch) have hinted at the presence of
extra relativistic degrees of freedom, the so-called "dark radiation." We
present a model independent study to account for the dark radiation by means of
the right-handed partners of the three, left-handed, standard model neutrinos.
We show that milli-weak interactions of these Dirac states (through their
coupling to a TeV-scale Z' gauge boson) may allow the \nu_R's to decouple much
earlier, at a higher temperature, than their left-handed counterparts. If the
\nu_R's decouple during the quark-hadron crossover transition, they are
considerably cooler than the \nu_L's and contribute less than 3 extra
"equivalent neutrinos" to the early Universe energy density. For decoupling in
this transition region, the 3 \nu_R generate \Delta N_\nu = 3(T_{\nu_R}/T_{\nu_
L})^4 < 3, extra relativistic degrees of freedom at BBN and at the CMB epochs.
Consistency with present constraints on dark radiation permits us to identify
the allowed region in the parameter space of Z' masses and couplings.
Remarkably, the allowed region is within the range of discovery of LHC14.
