U(1) Symmetry Restoration and Effective Neutrino Species
arXiv:1403.6460 · doi:10.1016/j.physletb.2014.05.048
Abstract
The U(1) symmetry could be restored during inflation, since the BICEP2 results suggest a GUT-scale inflation with the Hubble parameter, GeV, close to the U(1) breaking scale. We consider a scenario in which the Higgs field dominates the Universe after inflation, and mainly decays into the U(1) gauge bosons, whose subsequent decays reheat the Universe. Interestingly, if one of the right-handed neutrinos is extremely light and behaves as dark radiation or hot dark matter, its abundance is determined by the charge assignment and the relativistic degree of freedom in plasma. We find that takes discrete values between and in the standard model plus three right-handed neutrinos, depending on whether the decay into heavier right-handed neutrinos are kinematically accessible or not. In the fiveness U(1) case, we find that takes discrete values between and . The tension between BICEP2 and {\it Planck} can be partially relaxed by dark radiation.
arXiv comment14 pages, v2: corrected small errors in calculations, conclusions unchanged
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