Reconciling BICEP2 and Planck results with right-handed Dirac neutrinos in the fundamental representation of grand unified E6

The tensor-to-scalar ratio (r = 0.201:g) inferred from the excess B-mode power observed by the Background Imaging of Cosmic Extragalactic Polarization (BICEP2) experiment is almost twice as large as the 95% CL upper limits derived from temperature measurements of the WMAP (r < 0.13) and Planck (r < 0.11) space missions. Very recently, it was suggested that additional relativistic degrees of freedom beyond the three active neutrinos and photons can help to relieve this tension: the data favor an effective number of light neutrino species N-eff = 3.86 +/- 0.25. Since the BICEP2 ratio implies the energy scale of inflation (V-*(1/4) similar to 2 x 10(16) GeV) is comparable to the grand unification scale, in this paper we investigate whether we can accommodate the required N-eff with three right-handed (partners of the left-handed standard model) neutrinos living in the fundamental representation of a grand unified exceptional E-6 group. We show that the superweak interactions of these Dirac states (through their coupling to a TeV-scale Z' gauge boson) lead to decoupling of right-handed neutrino just above the QCD cross over transition: 175 MeV less than or similar to T-vR(dec) less than or similar to 250 MeV. For decoupling in this transition region, the contribution of the three right-handed neutrinos to N-eff is suppressed by heating of the left-handed neutrinos (and photons). Consistency (within 1 sigma) with the favored N-eff is achieved for 4.5 TeV < M-Z' < 7.5 TeV. The model is fully predictive and can be confronted with future data from LHC14.