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Register a new userSizeable theta_13 from the Charged Lepton Sector in SU(5), (Tri-)Bimaximal Neutrino Mixing and Dirac CP Violation
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The recent results from T2K and MINOS experiments point towards a relatively large value of the reactor angle theta_13 in the lepton sector. In this paper we show how a large theta_13 can arise from the charged lepton sector alone in the context of an SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the neutrino sector is still a viable possibility. We also analyse the general implications of the considered scenario for the searches of CP violation in neutrino oscillations.
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We study the CP violation in the deviation from the tri-bimaximal mixing (TBM) of neutrinos. We examine non-trivial relations among the mixing angles and the CP violating Dirac phase in the typical four cases of the deviation from the TBM. The first two cases are derived by the additional rotation of the 2-3 or 1-3 generations of neutrinos in the TBM basis. The other two cases are given by the additional rotation of the 1-3 or 1-2 generations of charged leptons with the TBM neutrinos. These four cases predict different relations among three mixing angles and the CP violating Dirac phase. The rotation of the 2-3 generations of neutrinos in the TBM basis predicts $sin ^2theta _{12}<1/3$, and the CP violating Dirac phase to be $pm (0.09pisim 0.76pi)$ for NH ($pm (0.15pisim 0.73pi) text{for IH}$) depending on $sin ^2theta _{23}$. The rotation of the 1-3 generations of neutrinos in the TBM basis gives $sin ^2theta _{12}>1/3$. The CP violating Dirac phase is not constrained by the input of the present experimental data. For the case of the 1-3 and 1-2 rotations of charged leptons in the TBM basis, the CP violating Dirac phase is predicted in $pm(0.35pisim 0.60pi)$ depending on $sin ^2theta _{12}$ for both NH and IH cases. We also discuss the specific case that $theta_{13}$ is related with the Cabibbo angle $lambda$ such as $sintheta_{13}=lambda/sqrt{2}$, in which the maximal CP violation is preferred. The CP violating Dirac phase can distinguish the lepton flavor mixing patterns at T2K and NO$ u$A experiments in the future.
We construct a model for tri-bimaximal lepton mixing which employs only family symmetries and their soft breaking; neither vacuum alignment nor supersymmetry, extra dimensions, or non-renormalizable terms are used in our model. It is an extension of the Standard Model making use of the seesaw mechanism with five right-handed neutrino singlets. The scalar sector comprises four Higgs doublets and one complex gauge singlet. The horizontal symmetry of our model is based on the permutation group S_3 of the lepton families together with the three family lepton numbers--united this constitutes a symmetry group Delta(6infty^2). The model makes no predictions for the neutrino masses.
We propose an extension of tri-bimaximal mixing to include a non-zero reactor angle $theta_{13}$ while maintaining the tri-bimaximal predictions for the atmospheric angle $theta_{23}=45^o$ and solar angle $theta_{12}=35^o$. We show how such tri-bimaximal-reactor mixing can arise at leading order from the(type I) see-saw mechanism with partially constrained sequential dominance. Partially constrained sequential dominance can be realized in GUT models with a non-Abelian discrete family symmetry, such as $A_4$, spontaneously broken by flavons with a particular vacuum alignment.
Inspired by the recent T2K indication of a relatively large theta_{13}, we provide a systematic study of some general modifications to three mostly discussed neutrino mixing patterns, i.e., tri-bimaximal, bimaximal and democratic mixing matrices. The correlation between theta_{13} and two large mixing angles are provided according to each modifications. The phenomenological predictions of theta_{12} and theta_{23} are also discussed. After the exclusion of several minimal modifications, we still have reasonable predictions of three mixing angles in 3 Sigma level for other scenarios.
Current experimental data allow the zero value for one neutrino mass, either m_1 = 0 or m_3 = 0. This observation implies that a realistic neutrino mass texture can be established by starting from the limit (a) m_1 = m_2 = 0 and m_3 eq 0 or (b) m_1 = m_2 eq 0 and m_3 = 0. In both cases, we may introduce a particular perturbation which ensures the resultant neutrino mixing matrix to be the tri-bimaximal mixing pattern or its viable variations with all entries being formed from small integers and their square roots. We find that it is natural to incorporate this kind of neutrino mass matrix in the minimal Type-II seesaw model with only one heavy right-handed Majorana neutrino N in addition to the SU(2)_L Higgs triplet Delta_L. We show that it is possible to account for the cosmological baryon number asymmetry in the m_3 =0 case via thermal leptogenesis, in which the one-loop vertex correction to N decays is mediated by Delta_L and the CP-violating asymmetry of N decays is attributed to the electron flavor.
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