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 } \lesssim T _ { \nu _ { R } } ^ { dec } \lesssim 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 ^ { 4 } He 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 .