Browsing by Author "Petcov, Serguey T."
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Item The Absolute Neutrino Mass Scale, Neutrino Mass Spectrum, Majorana CP-Violation and Neutrinoless Double-Beta Decay(2006-09-25T15:37:55Z) Pascoli, Silvia; Petcov, Serguey T.; Schwetz, Thomas; Physics; Elementary Particle TheoryAssuming 3-$\nu$ mixing, massive Majorana neutrinos and neutrinoless double-beta (\betabeta-) decay generated only by the (V-A) charged current weak interaction via the exchange of the three Majorana neutrinos, we briefly review the predictions for the effective Majorana mass $\meff$ in \betabeta-decay and reanalyse the physics potential of future \betabeta-decay experiments to provide information on the type of neutrino mass spectrum, the absolute scale of neutrino masses, and Majorana CP-violation in the lepton sector. Using as input the most recent experimental results on neutrino oscillation parameters and the prospective precision that can be achieved in future measurements of the latter, we perform a statistical analysis of a \betabeta-decay half-life measurement taking into account experimental and theoretical errors, as well as the uncertainty implied by the imprecise knowledge of the corresponding nuclear matrix element (NME). We show, in particular, how the possibility to dis...Item Charged Lepton Decays L_i to L_j + gamma, Leptogenesis CP-Violating Parameters and Majorana Phases(2006-06-13T07:46:15Z) Petcov, Serguey T.; Shindou, Tetsuo; Physics; Elementary Particle TheoryWe 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, .Item A comment on the measurement of neutrino masses in beta-decay experiments(2006-05-11T10:49:55Z) Bilenky, Samoil M.; Mateev, Matey D.; Petcov, Serguey T.; Physics; Elementary Particle TheoryWe discuss the physics potential of future tritium beta-decay experiments having a sensitivity to a neutrino mass ~\sqrt{|\Delta m^{2}_{23}|}~5x10^{-2} eV. The case of three-neutrino mixing is analised. A negative result of such an experiment would imply that the neutrino mass spectrum is of normal hierarchical type. The interpretation of a positive result would depend on the value of the lightest neutrino mass; if the lightest neutrino mass satisfies the inequality min(m_j) << \sqrt{|\Delta m^{2}_{23}|}, it would imply that the neutrino mass spectrum is of the inverted hierarchical type.Item Connecting Low Energy Leptonic CP-violation to Leptogenesis(2006-12-11T10:38:24Z) Pascoli, Silvia; Petcov, Serguey T.; Riotto, Antonio; Physics; Elementary Particle TheoryIt was commonly thought that the observation of low energy leptonic CP-violating phases would not automatically imply the existence of a baryon asymmetry in the leptogenesis scenario. This conclusion does not generically hold when the issue of flavour is relevant and properly taken into account in leptogenesis. We illustrate this point with various examples studying the correlation between the baryon asymmetry and the CP-violating asymmetry in neutrino oscillations and the effective Majorana mass in neutrinoless double beta decay.Item CP violation due to multi Froggatt-Nielsen fields(2007-05-15T12:00:46Z) Kanemura, Shinya; Matsuda, Koichi; Ota, Toshihiko; Petcov, Serguey T.; Shindou, Tetsuo; Takasugi, Eiichi; Physics; Elementary Particle TheoryWe study how to incorporate CP violation in the Froggatt--Nielsen (FN) mechanism. To this end, we introduce non-renormalizable interactions with a flavor democratic structure to the fermion mass generation sector. It is found that at least two iso-singlet scalar fields with imposed a discrete symmetry are necessary to generate CP violation due to the appearance of the relative phase between their vacuum expectation values.Item Determining the Neutrino Mass Hierarchy with Atmospheric Neutrinos(2005) Petcov, Serguey T.; Schwetz, Thomas; Physics; Elementary Particle TheoryThe possibility to determine the type of neutrino mass hierarchy by studying atmospheric neutrino oscillations with a detector capable to distinguish between neutrino and antineutrino events, such as magnetized iron calorimeters, is considered. We discuss how the ability to distinguish between the neutrino mass spectrum with normal and inverted hierarchy depends on detector characteristics like neutrino energy and direction resolutions or charge miss-identification, and on the systematical uncertainties related to the atmospheric neutrino fluxes...Item Leptogenesis and Low Energy CP Violation in Neutrino Physics(2006-12-07T15:48:44Z) Pascoli, Silvia; Petcov, Serguey T.; Riotto, Antonio; Physics; Elementary Particle TheoryTaking into account the recent progress in the understanding of the lepton flavour effects in leptogenesis, we investigate in detail the possibility that the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana CP-violating phases in the PMNS neutrino mixing matrix U, and thus is directly related to the low energy CP-violation in the lepton sector (e.g., in neutrino oscillations, etc.). We first derive the conditions of CP-invariance of the neutrino Yukawa couplings lambda in the see-saw Lagrangian, and of the complex orthogonal matrix R in the ``orthogonal'' parametrisation of lambda. We show, e.g. that under certain conditions i) real R and specific CP-conserving values of the Majorana and Dirac phases can imply CP-violation, and ii) purely imaginary R does not necessarily imply breaking of CP-symmetry. We study in detail the case of hierarchical heavy Majorana neutrino mass spectrum, presenting results for three possible types of light neutrino mass spectrum: i) normal hierarchical, ii) inverted hierarchical, and iii) quasi-degenerate. Results in the alternative case of quasi-degenerate in mass heavy Majorana neutrinos, are also derived. The minimal supersymmetric extension of the Standard Theory with right-handed Majorana neutrinos and see-saw mechanism of neutrino mass generation is discussed as well. We illustrate the possible correlations between the baryon asymmetry of the Universe and i) the rephasing invariant J_CP controling the magnitude of CP-violation in neutrino oscillations, or ii) the effective Majorana mass in neutrinoless double beta decay, in the cases when the only source of CP-violation is respectively the Dirac or the Majorana phases in the neutrino mixing matrix.Item Majorana CP-Violating Phases, RG Running of Neutrino Mixing Parameters and Charged Lepton Flavour Violating Decays(2005) Petcov, Serguey T.; Shindou, Tetsuo; Takanishi, Yasutaka; Physics; Elementary Particle TheoryWe 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 µ → epsilon + gamma, tau → µ + 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 Yv which can be expressed in terms of the light and heavy right-handed (RH) neutrino masses, neutrino mixing matrix UPMNS, and an orthogonal matrix R. We investigate the effects of Majorana CP-violation phases in UPMNS, and of the RG running of light neutrino masses and mixing angles from MZ to the RH Majorana neutrino mass scale MR, on the predictions for the rates of LFV decays µ → epsilon + gamma, tau → µ+gamma and tau → epsilon+gamma. Results for neutrino mass spectrum with normal hierarchy, values of the lightest v-mass in the range 0 ≤ m1 ≤ 0.30 eV, and quasi-degenerate heavy RH Majorana neutrinos in the cases of R = 1 and complex matrix 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 µ → epsilon+gamma and tau → epsilon + gamma. The impact of these effects on the tau→µ+gamma decay rate is typically smaller and only possible for m1 >∼ 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 µ → epsilon + gamma and tau → epsilon + gamma (tau → µ + gamma) decays is entirely determined in the case of R ~= 1 by the values of the neutrino mixing parameters at MZ.Item Neutrino Oscillation Parameters After High Statistics KamLAND Results(2008-05-12T11:05:35Z) Bandyopadhyay, Abhijit; Choubey, Sandhya; Goswami, Srubabati; Petcov, Serguey T.; Roy, D.P.; Physics; Elementary Particle TheoryWe do a re-analysis to asses the impact of the results of the Borexino experiment and the recent 2.8 KTy KamLAND data on the solar neutrino oscillation parameters. The current Borexino results are found to have no impact on the allowed solar neutrino parameter space. The new KamLAND data causes a significant reduction of the allowed range of $\Delta m^2_{21}$, determining it with an unprecedented precision of 8.3% at 3$\sigma$. The precision of $\Delta m^2_{21}$ is controlled practically by the KamLAND data alone. Inclusion of new KamLAND results also improves the upper bound on $\sin^2\theta_{12}$, but the precision of this parameter continues to be controlled by the solar data. The third mixing angle is constrained to be $\sin^2\theta_{13} < 0.063$ at $3\sigma$ from a combined fit to the solar, KamLAND, atmospheric and CHOOZ results. We also address the issue of how much further reduction of allowed range of $\Delta m^2_{21}$ and $\sin^2\theta_{12}$ is possible with increased statistics from KamLAND. We find that there is a sharp reduction of the $3\sigma$ ``spread'' with enhanced statistics till about 10 KTy after which the spread tends to flatten out reaching to less than 4% with 15 KTy data. For $\sin^2\theta_{12}$ however, the spread is more than 25% even after 20 KTy exposure and assuming $\theta_{12} < \pi/4$, as dictated by the solar data. We show that with a KamLAND like reactor ``SPMIN'' experiment at a distance of $\sim$ 60 km, the spread of $\sin^2\theta_{12}$ could be reduced to about 5% at $3\sigma$ level while $\Delta m_{21}^2$ could be determined to within 4%, with just 3 KTy exposure.Item Nuclear matrix elements of 0 nu beta beta decay: Possible test of the calculations(2007-11-14T10:25:08Z) Bilenky, Samoil M.; Petcov, Serguey T.; Physics; Elementary Particle TheoryA possible model independent test of the theoretically calculated nuclear matrix elements of $0\nu\beta\beta$-decay is proposed. The test can be accomplished if $0\nu\beta\beta$-decay of three (or more) nuclei is observed. The selection of the nuclei for the next generation of $0\nu\beta\beta$-decay experiments should be done taking into account {\it also} considerations regarding the possibility to test the nuclear matrix element calculations.Item On the atmospheric neutrino oscillations, theta(13) and neutrino mass hierarchy(2007-11-14T10:32:54Z) Petcov, Serguey T.; Palomares-Ruiz, Sergio; Physics; Elementary Particle TheoryWe give predictions for the up-down asymmetry in the Nadir angle dependence of the ratio Nmu/Ne of the rates of the mu-like and e-like multi-GeV events measured in water-Cerenkov detectors (Super-Kamiokande, etc.) in the case of 3-neutrino oscillations of the atmospheric nu_e (antinu_e) and nu_mu (antinu_mu), driven by one neutrino mass squared difference, |Delta m^2_{atm}| = |Delta m^2_{31}| ~ (2.0 - 3.0) 10^{-3} eV^2 >> Delta m^2_{21} = Delta m^2_{sol}. This ratio is particularly sensitive to the Earth matter effects in the atmospheric neutrino oscillations, and thus to the values of sin^2(theta13) and sin^2(theta23), theta13 and theta23 being the neutrino mixing angle limited by the CHOOZ and Palo Verde experiments and that responsible for the dominant atmospheric nu_mu -> nu_tau (antinu_mu -> antinu_tau) oscillations, respectively. It is also sensitive to the type of neutrino mass spectrum which can be with normal (Delta m^2_{atm} > 0) or with inverted (Delta m^2_{atm} < 0) hierarchy.Item Precision measurement of solar neutrino oscillation parameters by a long-baseline reactor neutrino experiment in Europe(2006-07-26T08:30:19Z) Petcov, Serguey T.; Schwetz, Thomas; Physics; Elementary Particle TheoryWe consider the determination of the solar neutrino oscillation parameters $\Delta m^2_{21}$ and $\theta_{12}$ by studying oscillations of reactor anti-neutrinos emitted by nuclear power plants (located mainly in France) with a detector installed in the Frejus underground laboratory. The performances of a water Cerenkov detector of 147 kt fiducial mass doped with 0.1% of Gadolinium (MEMPHYS-Gd) and of a 50 kt scale liquid scintillator detector (LENA) are compared. In both cases 3$\sigma$ uncertainties below 3% on $\Delta m^2_{21}$ and of about 20% on $\sin^2\theta_{12}$ can be obtained after one year of data taking. The Gadolinium doped Super-Kamiokande detector (SK-Gd) in Japan can reach a similar precision if the SK/MEMPHYS fiducial mass ratio of 1 to 7 is compensated by a longer SK-Gd data taking time. Several years of reactor neutrino data collected by MEMPHYS-Gd or LENA would allow a determination of $\Delta m^2_{21}$ and $\sin^2\theta_{12}$ with uncertainties of approximately 1% and 10% at 3$\sigma$, respectively. These accuracies are comparable to those that can be reached in the measurement of the atmospheric neutrino oscillation parameters $\Delta m^2_{31}$ and $\sin^2\theta_{23}$ in long-baseline superbeam experiments.Item Predictions for Neutrino Masses, $ββ_{0ν}$-Decay and Lepton Flavor Violation in a SUSY $SU(5) \times T^{\prime}$ Model of Flavour(SISSA, 2011-09-04) Chen, M.-C.; Mahanthappa, Kalyana T.; Meroni, Aurora; Petcov, Serguey T.; Physics; Elementary Particle TheoryWe obtain predictions for the neutrino masses, the effective Majorana mass in neutrinoless double beta decay and for the rates of the lepton flavor violating processes $\mu\rightarrow e + \gamma$, $\tau \rightarrow e + \gamma$ and $ \tau \rightarrow \mu + \gamma$ in a SUSY $SU(5) \times T^{\prime}$ Model of flavour, which gives rise to realistic masses and mixing patterns for quarks and leptons.Item The See-Saw Mechanism, Neutrino Yukawa Couplings, LFV Decays l_i to l_j + gamma and Leptogenesis(2005) Petcov, Serguey T.; Rodejohann, Werner; Shindou, Tetsuo; Takanishi, Yasutaka; Physics; Elementary Particle TheoryThe LFV charged lepton decays mu to e + gamma, tau to e + gamma and tau to mu + gamma and thermal leptogenesis are analysed in the MSSM with see-saw mechanism of neutrino mass generation and soft SUSY breaking with universal boundary conditions. The case of hierarchical heavy Majorana neutrino mass spectrum, M_1 << M_2 << M_3, is investigated.Item Solar Model Parameters and Direct Measurements of Solar Neutrino Fluxes(2006-09-07T10:32:29Z) Bandyopadhyay, Abhijit; Choubey, Sandhya; Goswami, Srubabati; Petcov, Serguey T.; Physics; Elementary Particle TheoryWe explore a novel possibility of determining the solar model parameters, which serve as input in the calculations of the solar neutrino fluxes, by exploiting the data from direct measurements of the fluxes. More specifically, we use the rather precise value of the $^8B$ neutrino flux, $\phi_B$ obtained from the global analysis of the solar neutrino and KamLAND data, to derive constraints on each of the solar model parameters on which $\phi_B$ depends. We also use more precise values of $^7Be$ and $pp$ fluxes as can be obtained from future prospective data and discuss whether such measurements can help in reducing the uncertainties of one or more input parameters of the Standard Solar Model.Item A SUSY SU(5)xT' Unified Model of Flavour with large θ_{13}(SISSA, 2012-05-23) Meroni, Aurora; Petcov, Serguey T.; Spinrath, Martin; Physics; Elementary Particle TheoryWe present a SUSY SU(5)xT' unified flavour model with type I see-saw mechanism of neutrino mass generation, which predicts the reactor neutrino angle to be \theta_{13} = 0.14 close to the recent results from the Daya Bay and RENO experiments. The model predicts also values of the solar and atmospheric neutrino mixing angles, which are compatible with the existing data. The T' breaking leads to tri-bimaximal mixing in the neutrino sector, which is perturbed by sizeable corrections from the charged lepton sector. The model exhibits geometrical CP violation, where all complex phases have their origin from the complex Clebsch-Gordan coefficients of T'. The values of the Dirac and Majorana CP violating phases are predicted. For the Dirac phase in the standard parametrisation of the neutrino mixing matrix we get a value close to 90 degrees \delta = \pi/2 - 0.45 \theta^c = 84.3 degrees, \theta^c being the Cabibbo angle. The neutrino mass spectrum can be with normal ordering (2 cases) or inverted ordering. In each case the values of the three light neutrino masses are predicted with relatively small uncertainties, which allows to get also unambiguous predictions for the neutrinoless double beta decay effective Majorana mass.Item Theoretical Prospects of Neutrinoless Double Beta Decay(2005) Petcov, Serguey T.; Physics; Elementary Particle TheoryThe compelling experimental evidences for oscillations of solar and atmospheric neutrinos imply the existence of 3-neutrino mixing in vacuum. We briefly review the phenomenology of 3-v mixing, and the current data on the 3-neutrino mixing parameters. The open questions and the main goals of future research in the field of neutrino mixing and oscillations are outlined. The predictions for the effective Majorana mass || in (betabeta)0v-decay in the case of 3-v mixing and massive Majorana neutrinos are reviewed. The physics potential of the experiments, searching for (betabeta)0v-decay and having sensitivity to || >~ 0.01 eV, for providing information on the type of the neutrino mass spectrum, on the absolute scale of neutrino masses and on the Majorana CP-violation phases in the PMNS neutrino mixing matrix, is discussed.Item U_{PMNS} = U_ell^dagger U_nu(2007-08-09T12:57:46Z) Hochmuth, K.A.; Petcov, Serguey T.; Rodejohann, Werner; Physics; Elementary Particle TheoryWe consider corrections to vanishing U_{e3} and maximal atmospheric neutrino mixing originating from the relation U = U_ell^dagger U_nu, where U is the PMNS mixing matrix and U_ell (U_nu) is associated with the diagonalization of the charged lepton (neutrino) mass matrix. We assume that in the limit of U_ell or U_nu being the unit matrix, one has U_{e3} = 0 and theta_{23} = pi/4, while the solar neutrino mixing angle is a free parameter. Well-known special cases of the indicated scenario are the bimaximal and tri-bimaximal mixing schemes. If U_{e3} \neq 0 and theta_{23} \neq pi/4 due to corrections from the charged leptons, |U_{e3}| can be sizable (close to the existing upper limit) and we find that the value of the solar neutrino mixing angle is linked to the magnitude of CP violation in neutrino oscillations. In the alternative case of the neutrino sector correcting U_{e3} = 0 and theta_{23} = pi/4, we obtain a generically smaller |U_{e3}| than in the first case. Now the magnitude of CP violation in neutrino oscillations is connected to the value of the atmospheric neutrino mixing angle theta_{23}. We find that both cases are in agreement with present observations. We also introduce parametrization independent "sum-rules" for the oscillation parameters.