Kinetic equations for baryogenesis via sterile neutrino oscillation

Abstract

We investigate baryogenesis in the νMSM (neutrino Minimal Standard Model), which is the MSM extended by three right-handed neutrinos with masses below the electroweak scale. The baryon asymmetry of the universe can be generated by the mechanism via flavor oscillation of right-handed (sterile) neutrinos which are responsible to masses of active neutrinos confirmed by various experiments. We present the kinetic equations for the matrix of densities of leptons which describe the generation of asymmetries. Especially, the momentum dependence of the matrix of densities is taken into account. By solving these equations numerically, it is found that the momentum distribution is significantly distorted from the equilibrium one, since the production for the modes with lower momenta k ≪ T (T is the temperature of the universe) is enhanced, while suppressed for higher modes. As a result, the most important mode for the yields of sterile neutrinos as well as the baryon asymmetry is k ≃ 2T , which is smaller than k inferred from the thermal average. The comparison with the previous works is also discussed.

GeV-scale hot sterile neutrino oscillations: a derivation of evolution equations

“…refs. [4][5][6][7][8][9][10][11][12][13][14][15]), with the goal of moving from model computations towards first principles analyses.…”

“…refs. [4][5][6][7][8][9][10][11][12][13][14][15] and references therein). The main novelties of our investigation are the full inclusion of both helicity-flipping and conserving contributions (or, in the language of section 2.6, fermion-number conserving and violating effects); the inclusion of all chemical potentials and gauge field expectation values induced by them; a consistent leading-order computation of all coefficients parametrizing the equations, both in the "symmetric" and in the "Higgs" phase; as well as a formulation general enough to permit for the treatment of the regime in which the sphaleron processes gradually switch off.…”

Lepton asymmetry from mixing and oscillations

“…The impact of flavour oscillations can be accounted for through the quantum improvement of the classical Boltzmann equations by promoting the number densities of individual flavours to a matrix of densities [43], thereby allowing for flavour coherences. This approach yields the so-called density matrix formalism, which has been applied extensively to scenarios of leptogenesis [9,10,21,24,28,[44][45][46][47][48][49]. On the other hand, a semi-classical treatment of mixing is possible through the inclusion of effective Yukawa couplings [15,35], which can account for the ε-and ε -type CP violation, arising respectively from self-energy and vertex effects.…”

Baryogenesis from L -violating Higgs-doublet decay in the density-matrix formalism

“…In the framework of the type-I seesaw model of neutrino masses with right-handed (RH) neutrinos below the electroweak scale, there exists a well-known mechanism to account for the baryon asymmetry of the Universe, through oscillations of right-handed neutrinos [1][2][3][4][5][6][7][8][9][10][11][12][13]. This Akhmedov-Rubakov-Smironv (ARS) scenario is based on the generation of particle-antiparticle asymmetries for the various lepton flavours.…”