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Neutrino Cosmology after WMAP and LHC7

Luis Alfredo Anchordoqui, Haim Goldberg

Abstract

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_{ν_R}^{dec} < 250 MeV. In this transitional region, the residual temperature ratio between ν_L and ν_R generates extra relativistic degrees of freedom at BBN and at the CMB epochs. Consistency (within 1σ) 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.

Neutrino Cosmology after WMAP and LHC7

Abstract

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_{ν_R}^{dec} < 250 MeV. In this transitional region, the residual temperature ratio between ν_L and ν_R generates extra relativistic degrees of freedom at BBN and at the CMB epochs. Consistency (within 1σ) 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.

Paper Structure

This paper contains 23 equations, 1 figure, 1 table.

Figures (1)

  • Figure 1: Dark shaded areas show region allowed from decoupling requirements to accommodate WMAP and BBN data. Light shaded regions indicate the masses excluded by the LHC7 dijet searches. The dark shaded areas in the left and right figures pertain to chemical and thermal equilibrium, respectively. These two estimates should serve to bracket the size of the actual effect. The designation of $B$ corresponds to $Z'$ and $B-L$ to $Z"$.