Leptogenesis In Models Research Articles

Supersymmetric model of neutrino mass and leptogenesis with string-scale unification

Adjoint supermultiplets (1,3,0) and (8,1,0) modify the evolution of gauge couplings. If the unification of gauge couplings occurs at the string scale, their masses are fixed at around $10^{13}$ GeV. This scale coincides with expected gaugino condensation scale in the hidden sector $M_{string}^{2/3} m^{1/3}_{3/2} \sim 10^{13}$ GeV. We show how neutrino masses arise in this unified model which naturally explain the present atmospheric and solar neutrino data. The out-of-equilibrium decay of the superfield (1,3,0) at $10^{13}$ GeV may also lead to a lepton asymmetry which then gets converted into the present observed baryon asymmetry of the Universe.

Supersymmetric triplet Higgs model of neutrino masses and leptogenesis

We construct a supersymmetric version of the triplet Higgs model for neutrino masses, which can generate a baryon asymmetry of the Universe through lepton-number violation and is consistent with the gravitino constraints.

The minimal supersymmetric leptogenesis

We reanalyze the supersymmetric leptogenesis model by one of the authors (HM) and Yanagida based on \tilde{L} = H_u flat direction in detail. We point out that the appropriate amount of baryon asymmetry can be generated in this model with the neutrino mass matrix consistent with the atmospheric neutrino oscillation and solutions to the solar neutrino problem, preferably the small angle MSW solution. The reheating temperature can be low enough to avoid the cosmological gravitino problem. This model is the minimal one because it does not rely on any new physics beyond supersymmetry and Majorana neutrino masses.

Leptogenesis in theories with large extra dimensions

We study the scenario of baryogenesis through leptogenesis in higher-dimensional theories, in which the scale of quantum gravity is many orders of magnitude smaller than the usual Planck mass. The minimal realization of these theories includes an isosinglet neutrino which feels the presence of large compact dimensions, whereas all the SM particles are localized on a $(1+3)$-dimensional subspace. In the formulation of minimal leptogenesis models, we pay particular attention to the existence of Majorana spinors in higher dimensions. After compactification of the extra dimensions, we obtain a tower of Majorana Kaluza-Klein excitations which act as an infinite series of CP-violating resonators and derive the necessary conditions for their constructive interference. Based on this CP-violating mechanism, we find that the decays of the heavy Majorana excitations can produce a leptonic asymmetry which is reprocessed into the observed baryonic asymmetry of the universe by means of out-of-equilibrium sphaleron interactions, provided the reheat temperature is above 5 GeV.

Gravitino constraints on models of neutrino masses and leptogenesis

In the supersymmetric extensions of the standard model, neutrino masses and leptogenesis require the existence of new particles. We point out that if these particles with lepton number violating interactions have standard model gauge interactions, then they may not be created after reheating because of the gravitino problem. This will rule out all existing models of neutrino masses and leptogenesis, except the one with right-handed singlet neutrinos.

Scale of SU(2) R symmetry breaking and leptogenesis

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an SU(2) R gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that m N ≳10 16 GeV if m N > m W R , and m W R ≳2×10 5 GeV(m N/10 2 GeV) 3/4 if m N < m W R , where m N is the mass of the lightest right-handed neutrino. A better bound m W R ≳3×10 6 GeV(m N/10 2 GeV) 2/3 is obtained if leptogenesis occurs at T> m W R . We show also that the m N > m W R option is excluded in a supersymmetric theory with gravitinos.

CP-violation in the mass matrix of heavy neutrinos

We discuss the question of CP-violation in the effective Hamiltonian approach in models of leptogenesis through heavy right handed neutrino decays. We first formulate the problem in four component notation and then point out that before the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in the heavy neutrinos. However, the lepton asymmetry generated after they completely decay are independent of this asymmetry.