Dark Radiation Confronting LHC in Z' Models
  Recent cosmological data favour additional relativistic degrees of freedom
beyond the three active neutrinos and photons, often referred to as "dark
radiation". Extensions of the SM involving TeV-scale Z' gauge bosons
generically contain superweakly interacting light right-handed neutrinos which
can constitute this dark radiation. In this letter we confront the requirement
on the parameters of the E6 Z' models to account for the present evidence of
dark radiation with the already existing constraints from searches for new
neutral gauge bosons at LHC7.
