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Register a new userManifestations of non-zero Majorana CP violating phases in oscillations of supernova neutrinos
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We investigate effects of non-zero Dirac and Majorana CP violating phases on neutrino-antineutrino oscillations in a magnetic field of astrophysical environments. It is shown that in the presence of strong magnetic fields and dense matter, non-zero CP phases can induce new resonances in the oscillations channels $ u_e leftrightarrow bar{ u}_e$, $ u_e leftrightarrow bar{ u}_mu$ and $ u_e leftrightarrow bar{ u}_{tau}$. We also consider all other possible oscillation channels with $ u_mu$ and $ u_tau$ in the initial state. The resonances can potentially lead to significant phenomena in neutrino oscillations accessible for observation in experiments. In particular, we show that neutrino-antineutrino oscillations combined with Majorana-type CP violation can affect the $bar{ u}_e$/$ u_e$ ratio for neutrinos coming from the supernovae explosion. This effect is more prominent for the normal neutrino mass ordering. The detection of supernovae neutrino fluxes in the future experiments, such as JUNO, DUNE and Hyper-Kamiokande, can give an insight into the nature of CP violation and, consequently, provides a tool for distinguishing the Dirac or Majorana nature of neutrinos.
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The evolution equation for active and sterile neutrinos propagating in general anisotropic or polarized background environment is found and solved for a special case when heavy neutrinos do not decouple, resulting in non-unitary mixing among light neutrino states. Then new CP violating neutrino oscillation effects appear. In contrast to the standard unitary neutrino oscillations these effects can be visible even for two flavour neutrino transitions and even if one of the elements of the neutrino mixing matrix is equal to zero. They do not necessarily vanish with $delta m^{2} to 0$ and they are different for various pairs of flavour neutrino transitions ($ u_e to u_mu$), ($ u_mu to u_tau$), ($ u_tau to u_e$). Neutrino oscillations in vacuum and Earths matter are calculated for some fixed baseline experiments and a comparison between unitary and non-unitary oscillations are presented. It is shown, taking into account the present experimental constraints, that heavy neutrino states can affect CP and T asymmetries. This is especially true in the case of $ u_mu to u_tau$ oscillations.
We consider the MSSM with see-saw mechanism of neutrino mass generation and soft SUSY breaking with flavour-universal boundary conditions at the GUT scale, in which the lepton flavour violating (LFV) decays muto e + gamma, tauto mu + gamma, etc.,are predicted with rates that can be within the reach of present and planned experiments. These predictions depend critically on the matrix of neutrino Yukawa couplings bf{Y_{ u}} which can be expressed in terms of the light and heavy right-handed (RH) neutrino masses, neutrino mixing matrix U_{PMNS}, and an orthogonal matrix bf{R}. We investigate the effects of Majorana CP-violation phases in U_{PMNS}, and of the RG running of light neutrino masses and mixing angles from M_Z to the RH Majorana neutrino mass scale M_R, on the predictions for the rates of LFV decays muto e + gamma, tau to mu + gamma and tauto e + gamma. Results for neutrino mass spectrum with normal hierarchy, values of the lightest u-mass in the range 0 leq m_1 leq 0.30 eV, and quasi-degenerate heavy RH Majorana neutrinos in the cases of bf{R} = bf{1} and complex matrix bf{R} are presented. We find that the effects of the Majorana CP-violation phases and of the RG evolution of neutrino mixing parameters can change by few orders of magnitude the predicted rates of the LFV decays mu to e + gamma and tau to e + gamma. The impact of these effects on the tau to mu + gamma decay rate is typically smaller and only possible for m_1 > 0.10 eV. If the RG running effects are negligible, in a large region of soft SUSY breaking parameter space the ratio of the branching ratios of the mu to e + gamma and tau to e + gamma (tau to mu + gamma) decays is entirely determined in the case of bf{R} cong bf{1} by the values of the neutrino mixing parameters at M_Z.
Recent studies about the impact of the CP-violating complex parameters in supersymmetry on the decays of third generation squarks and about T-odd asymmetries in neutralino and chargino production and decay are reviewed. The CP-even branching ratios of the third generation squarks show a pronounced dependence on the phases of A_t, A_b, mu and M_1 in a large region of the supersymmetric parameter space. This could have important implications for stop and sbottom searches and the MSSM parameter determination in future collider experiments. We have estimated the expected accuracy in the determination of the parameters by global fits of measured masses, decay branching ratios and production cross sections. We have found that the parameter A_t can be determined with an error of 2 - 3%, whereas the error on A_b is likely to be of the order of 50 - 100%. In addition we have studied CP-odd observables, like asymmetries based on triple product correlations, which are necessary to unambiguously establish CP violation. We have analysed these asymmetries in neutralino and chargino production with subsequent three-body decays at the International Linear Collider with longitudinally polarised beams in the MSSM with complex parameters M_1 and mu. The asymmetries, which appear already at tree-level because of spin correlation between production and decay, can be as large as 20% and will therefore be an important tool for the search for CP-violating effects in supersymmetry.
We propose a new strategy for detecting the CP-violating phases and the effective mass of muon Majorana neutrinos by measuring observables associated with neutrino-antineutrino oscillations in $pi^{pm}$ decays. Within the generic framework of quantum field theory, we compute the non-factorizable probability for producing a pair of same-charged muons in $pi^{pm}$ decays as a distinctive signature of $ u_{mu}-bar{ u_{mu}}$ oscillations. We show that an intense neutrino beam through a long baseline experiment is favored for probing the Majorana phases. Using the neutrino-antineutrino oscillation probability reported by MINOS collaboration, a new stringent bound on the effective muon-neutrino mass is derived.
We analyse the dependence of the rates of the LFV charged lepton decays mu to e + gamma, tau to e + gamma, tau to mu + gamma (l_i to l_j + gamma) and their ratios, predicted in the class of SUSY theories with see-saw mechanism of nu-mass generation and soft SUSY breaking with universal boundary conditions at the GUT scale, on the Majorana CP-violation phases in the PMNS neutrino mixing matrix and the ``leptogenesis CP-violating (CPV) parameters. The case of quasi-degenerate in mass heavy Majorana neutrinos is considered. The analysis is performed for normal hierarchical (NH), inverted hierarchical (IH) and quasi-degenerate (QD) light neutrino mass spectra. We show, in particular, that for NH and IH nu-mass spectrum and negligible lightest neutrino mass, all three l_i to l_j + gamma decay branching ratios, BR(l_i to l_j + gamma), depend on one Majorana phase, one leptogenesis CPV parameter and on the 3-neutrino oscillation parameters; if the CHOOZ mixing angle theta_13 is sufficiently large, they depend on the Dirac CPV phase in the PMNS matrix. The ``double ratios R(21/31) sim BR(mu to e + gamma)/BR(tau to e + gamma) and R(21/32) sim BR(mu to e + gamma)/BR(tau to mu + gamma) are determined by these parameters. The same Majorana phase enters into the NH and IH expressions for the effective Majorana mass in neutrinoless double beta decay, <m>.
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