Neutrino Cosmology after WMAP and LHC7

Understand

The gauge-extended U(1)_C \times SU(2)_L \times U(1)_{I_R} \times U(1)_L model has the attractive property of elevating the two major global symmetries of the standard model (baryon number B and lepton number L) to local gauge symmetries.

• The U(1)_L symmetry prevents the generation of Majorana masses, leading to three superweakly interacting right-handed neutrinos.
• This also renders a B-L symmetry non-anomalous.
• We show that the superweak interactions of these Dirac states (through their coupling to the TeV-scale B-L gauge boson) permit right-handed neutrino decoupling just above the QCD phase transition: 175 MeV < T_{\nu_R}^{dec} < 250 MeV.