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Register a new userNormal hierarchy neutrino mass model revisited with leptogenesis
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We have studied the scenario of baryogenesis via leptogenesis in an $A_4$ flavor symmetric framework considering type I seesaw as the origin of neutrino mass. Because of the presence of the fifth generation right handed neutrino the model naturally generates non-zero reactor mixing angle. We have considered two vev alignments for the extra flavon $eta$ and studied the consequences in detail. As a whole the additional flavon along with the extra right handed neutrinos allow us to study thermal leptogenesis by the decay of the lightest right handed neutrino present in the model. We have computed the matter-antimatter asymmetry for both flavor dependent and flavor independent leptogenesis by considering a considerably wider range of right handed neutrino mass. Finally, we correlate the baryon asymmetry of the universe (BAU) with the model parameters and light neutrino masses.
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The effects of CP-phases on the three absolute quasi-degenerate Majorana neutrino (QDN) masses are stud-ied with neutrino mass matrices obeying {mu} - {tau} symmetry for normal as well as inverted hierarchical mass patterns. We have made further investigations on 1) the prediction of solar mixing angle which lies below tri-bimaximal mixing value in consistent with neutrino oscillation observational data, 2) the prediction on absolute neutrino mass parameter (mee) in 0{ u}{beta}{beta} decay, and 3) cosmological bound on the sum of the three absolute neutrino masses. The numerical analysis is carried out through the parameterization of neu- trino mass matrices using only two unknown parameters ({epsilon}, {eta}) within {mu} - {tau} symmetry. The results show the validity of QDN mass models in both normal and inverted hierarchical patterns. These models are far from discrimination and hence not yet ruled out. The results presented in this article are new and have subtle ef- fects in the discrimination of neutrino mass models.
Baryogenesis via leptogenesis is investigated in a specific model of light neutrino masses and mixing angles. The latter was proposed on the basis of an assumed complex-extended scaling property of the neutrino Majorana mass matrix $M_ u$, derived with a type-1 seesaw from a Dirac mass matrix $m_D$ and a heavy singlet neutrino Majorana mass matrix $M_R$. One of its important features, highlighted here, is that there is a common source of the origin of a nonzero $theta_{13}$ and the CP violating lepton asymmetry through the imaginary part of $m_D$. The model predicted CP violation to be maximal for the Dirac type and vanishing for the Majorana type. We assume strongly hierarchical mass eigenvalues for $M_R$. The leptonic CP asymmetry parameter $varepsilon^alpha_{1}hspace{1mm}$ with lepton flavor $alpha$, originating from the decays of the lightest of the heavy neutrinos $N_1$ (of mass $M_1$) at a temperature $Tsim M_1$, is what matters here with $varepsilon^alpha_{2,3}$, originating from the decays of $N_{2,3}$, being washed out. The light leptonic and heavy neutrino number densities (normalized to the entropy density) are evolved via Boltzmann equations down to electroweak temperatures to yield a baryon asymmetry through sphaleronic transitions. The effect of flavored vs. unflavored leptogenesis in the three mass regimes (1) $M_1<10^{9}$ GeV, (2) $10^9$ GeV $<M_1<$ $10^{12}$ GeV and (3) $M_1>10^{12}$ GeV are numerically worked out for both a normal and an inverted mass ordering of the light neutrinos. Corresponding results on the baryon asymmetry of the universe are obtained, displayed and discussed.
We review how a high-statistics observation of the neutrino signal from a future galactic core-collapse supernova (SN) may be used to discriminate between different neutrino mixing scenarios. Most SN neutrinos are emitted in the accretion and cooling phase, during which the flavor-dependent differences of the emitted neutrino spectra are small and rather uncertain. Therefore the discrimination between neutrino mixing scenarios using these neutrinos should rely on observables independent of the SN neutrino spectra. We discuss two complementary methods that allow for the positive identification of the mass hierarchy without knowledge of the emitted neutrino fluxes, provided that the 13-mixing angle is large, $sin^2theta_{13}gg 10^{-5}$. These two approaches are the observation of modulations in the neutrino spectra by Earth matter effects or by the passage of shock waves through the SN envelope. If the value of the 13-mixing angle is unknown, using additionally the information encoded in the prompt neutronization $ u_e$ burst--a robust feature found in all modern SN simulations--can be sufficient to fix both the neutrino hierarchy and to decide whether $theta_{13}$ is ``small or ``large.
The effects of the lightest neutrino mass in ``flavoured leptogenesis are investigated in the case when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in the neutrino mixing matrix U. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The ``orthogonal parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hierarchy) are obtained. It is shown, in particular, that if the matrix R is real and CP-conserving and the lightest neutrino mass m_3 in the case of inverted hierarchical spectrum lies the interval 5 times 10^{-4} eV < m_3 < 7 times 10^{-3} eV, the predicted baryon asymmetry can be larger by a factor of sim 100 than the asymmetry corresponding to negligible m_3 cong 0. As consequence, we can have successful thermal leptogenesis for 5 times 10^{-6} eV < m_3 < 5 times 10^{-2} eV even if R is real and the only source of CP-violation in leptogenesis is the Majorana and/or Dirac phase(s) in U.
Latest measurements have revealed that the deviation from a maximal solar mixing angle is approximately the Cabibbo angle, i.e. QLC relation. We argue that it is not plausible that this deviation from maximality, be it a coincidence or not, comes from the charged lepton mixing. Consequently we have calculated the required corrections to the exactly bimaximal neutrino mass matrix ansatz necessary to account for the solar mass difference and the solar mixing angle. We point out that the relative size of these two corrections depends strongly on the hierarchy case under consideration. We find that the inverted hierarchy case with opposite CP parities, which is known to guarantee the RGE stability of the solar mixing angle, offers the most plausible scenario for a high energy origin of a QLC-corrected bimaximal neutrino mass matrix. This possibility may allow us to explain the QLC relation in connection with the origin of the charged fermion mass matrices.
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