  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. In this transitional region, the residual
temperature ratio between \nu_L and \nu_R generates extra relativistic degrees
of freedom at BBN and at the CMB epochs. Consistency (within 1\sigma) with both
WMAP 7-year data and the most recent estimate of the primordial ^4He mass
fraction is achieved for 3 TeV < M_{B-L} < 6 TeV. The model is fully
predictive, and can be confronted with dijet and dilepton data (or lack
thereof) from LHC7 and, eventually, LHC14.
