arXiv subjects

S. T. Petcov

Publications and source records attributed to S. T. Petcov.

At least 127 records · Page 7Linked to original sources

arXiv2004

Update of the solar neutrino oscillation analysis with the 766 Ty KamLAND spectrum

We investigate the impact of the 766.3 Ty KamLAND spectrum data on the determination of the solar neutrino oscillation parameters. We show that the observed spectrum distortion in the KamLAND experiment firmly establishes $Δm^2_{21}$ to lie in the low-LMA solution region. The high-LMA solution is excluded at more than 4$σ$ by the global solar neutrino and KamLAND spectrum data. The maximal solar neutrino mixing is ruled out at $6σ$ level. The $3σ$ allowed region in the $Δm^2_{21}-\sin^2θ_{12}$ plane is found to be remarkably stable with respect to leaving out the data from one of the solar neutrino experiments from the global analysis. We perform a three flavor neutrino oscillation analysis of the global solar neutrino and KamLAND spectrum data as well. The $3σ$ upper limit on $\sin^2θ_{13}$ is found to be $ \sin^2θ_{13} <0.055$. We derive predictions for the CC to NC event rate ratio and day-night (D-N) asymmetry in the CC event rate, measured in the SNO experiment, and for the suppression of the event rate in the BOREXINO and LowNu experiments. Prospective high precision measurements of the solar neutrino oscillation parameters are also discussed.

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arXiv2004

Reactor Anti-Neutrino Oscillations and Gadolinium Loaded Super-Kamiokande Detector

We explore the potential of measuring the solar neutrino oscillation parameters in the proposed gadolinium loaded Super-Kamiokande (SK-Gd) detector. Gadolinium dissolved in water can detect neutrons much more efficiently than pure water. This imparts the detector the ability to observe electron type antineutrinos, transforming Super-Kamiokande into a huge reactor antineutrino detector with an event rate approximately 43 times higher than that observed in KamLAND. We simulate the reactor antineutrino data expected in this high statistics detector. We use these prospective data to study the precision with which the solar neutrino oscillation parameters, $Δm^2_{\odot}$ and $\sin^2θ_{\odot}$, can be determined i) with the SK-Gd detector, and ii) by combining the SK-Gd data with the global data on solar neutrino oscillations. For comparison and completeness the allowed regions of $Δm^2_{\odot}$ and $\sin^2θ_{\odot}$, expected to be obtained from the data of the solar neutrino and KamLAND experiments, are also presented.

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arXiv2004

Nuclear Matrix Elements of $0νββ$-Decay: Possible Test of the Calculations

A possible model independent test of the theoretically calculated nuclear matrix elements of $0νββ$-decay is proposed. The test can be accomplished if $0νββ$-decay of three (or more) nuclei is observed. The selection of the nuclei for the next generation of $0νββ$-decay experiments should be done taking into account {\it also} considerations regarding the possibility to test the nuclear matrix element calculations.

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arXiv2004

On the Atmospheric Neutrino Oscillations, theta13 and Neutrino Mass Hierarchy

We 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.

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arXiv2004

Three-Neutrino Oscillations of Atmospheric Neutrinos, theta13, Neutrino Mass Hierarchy and Iron Magnetized Detectors

We derive predictions for the Nadir angle (theta_n) dependence of the ratio Nmu-/Nmu+ of the rates of the mu- and mu+ multi-GeV events, and for the mu- - mu+ event rate asymmetry, A_{mu-mu+}=[Nmu- - Nmu+]/[Nmu- + Nmu+], in iron-magnetized calorimeter detectors (MINOS, INO) in the case of 3-neutrino oscillations of the atmospheric nu_mu and antinu_mu, driven by one neutrino mass squared difference, |Delta m^2_{31}| >> Delta m^2_{21}. The asymmetry A_{mu- mu+} (the ratio Nmu-/Nmu+) is shown to be 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 angles limited by the CHOOZ and Palo Verde experiments and that responsible for the dominant atmospheric nu_mu -> nu_tau (antinu_mu -> antinu_tau) oscillations. It is also very sensitive to the type of neutrino mass spectrum which can be with normal (Delta m^2_{31}>0) or with inverted (Delta m^2_{31} < 0) hierarchy. We find that for sin^2(theta23)>0.50, sin^2(2 theta13)>0.06 and Delta m^2_{31}=(2-3) 10^{-3} eV^2, the Earth matter effects produce a relative difference between the integrated asymmetries barA_{mu- mu+} and barA^{2nu}_{mu- mu+}$ in the mantle (cos(theta_n)=0.30-0.84) and core (cos(theta_n)=0.84-1.0) bins, which is bigger in absolute value than ~15%, can reach the values of (30-35)%, and thus can be sufficiently large to be observable. The sign of the indicated asymmetry difference is anticorrelated with the sign of Delta m^2_{31}. An observation of the Earth matter effects in the Nadir angle distribution of the asymmetry A_{mu- mu+} (ratio Nmu-/Nmu+) would clearly indicate that sin^2(2 theta13)>0.06 and sin^2(theta23)>0.50, and would lead to the determination of the sign of Delta m^2_{31}.

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arXiv2004

On Deviations from Bimaximal Neutrino Mixing

The PMNS neutrino mixing matrix U_{PMNS} is in general a product of two unitary matrices U_{lep} and U_ν arising from the diagonalization of the charged lepton and neutrino mass matrices, U_{PMNS} = U^{\dagger}_{lep} U_ν. Assuming that U_ν is a bimaximal mixing matrix, we investigate the possible forms of U_{lep}. We identify three possible generic structures of U_{lep}, which are compatible with the existing data on neutrino mixing. One corresponds to a hierarchical ``CKM-like'' matrix. In this case relatively large values of the solar neutrino mixing angle θ_{sol}, and of |U_{e3}|^2, are typically predicted, \tan^2θ_{sol} \gtap 0.42, |U_{e3}|^2 \gtap 0.02, while the atmospheric neutrino mixing angle θ_{atm} can deviate noticeably from π/4, \sin^2 2θ_{atm} \gtap 0.95. The second corresponds to one of the mixing angles in U_{lep} being equal to π/2, and predicts practically maximal atmospheric neutrino mixing \sin^2 2θ_{atm} \simeq 1. Large atmospheric neutrino mixing, \sin^2 2θ_{atm} \gtap 0.95, is naturally predicted by the third possible generic structure of U_{lep}, which corresponds to all three mixing angles in U_{lep} being large. We focus especially on the case of CP-nonconservation, analyzing it in detail. We show how the CP-violating phases, arising from the diagonalization of the neutrino and charged lepton mass matrices, contribute to the measured neutrino mixing observables.

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arXiv2003

Constraints on neutrino oscillation parameters from the SNO salt phase data

The physics implications of the just published salt phase data from the SNO experiment are examined. The effect of these data on the allowed ranges of the solar neutrino oscillation parameters, $Δ_m^2_{21}$ and $\sin^2θ_{12}$, are studied in the cases of two- and three- neutrino mixing. In the latter case we derive an upper limit on the angle $θ_{13}$. Constraints on the solar $ν_e$ transitions into a mixture of active and sterile neutrinos are also presented. Finally, we give predictions for the day-night asymmetry in the SNO experiment, for the event rate in the BOREXINO and LowNu experiments, and discuss briefly the constraints on the solar neutrino oscillation parameters which can be obtained with prospective KamLAND data.

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arXiv2003

Charged Lepton Flavor Violating Decays: Leading Logarithmic Approximation versus Full RG Results

In the context of the minimal supersymmetric extension of the Standard Model with the right-handed Majorana neutrinos, we study lepton flavor violating processes including full renormalization group running effects. We systematically compare our results with the commonly used leading logarithmic approximation, resorting to a ``best fit'' approach to fix all the high energy Yukawa matrices. We find significant deviations in large regions of the SUSY parameter space, which we outline in detail. We also give, within this setting, some results on the cosmo-phenomenologically preferred stau coannihilation region. Finally, we propose a parametrization, in terms of the SUSY input parameters, of the common SUSY mass appearing in the leading log and mass insertion approximation formula for the charged lepton flavor violating decay rates, which fits our full renormalization group results with high precision.

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arXiv2003

On the Measurement of Solar Neutrino Oscillation Parameters with KamLAND

A new reactor power plant Shika-2, with a power of approximately 4 GW and at a distance of about 88 km from the KamLAND detector is scheduled to start operating in March 2006. We study the impact of the $\barν_e$ flux from this reactor on the sensitivity of the KamLAND experiment to the solar neutrino oscillation parameters. We present results on prospective determination of $Δm^2_\odot$ and $\sin^2θ_\odot$ using the combined data from KamLAND and the solar neutrino experiments, including the effect of the Shika-2 contribution to the KamLAND signal and the latest data from the salt enriched phase of the SNO experiment. We find that contrary to the expectations, the addition of the Shika-2 reactor flux does not improve the $\sin^2θ_\odot$ sensitivity of KamLAND, while the ambiguity in $Δm^2_\odot$ measurement may even increase, as a result of the averaging effect between Kashiwazaki and the Shika-2 reactor contributions to the KamLAND signal.

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arXiv2003

Addendum: The SNO Solar Neutrino Data, Neutrinoless Double Beta-Decay and Neutrino Mass Spectrum

We update our earlier study in [1], which was inspired by the 2002 SNO data, on the implications of the results of the solar neutrino experiments for the predictions of the effective Majorana mass in neutrinoless double beta-decay, | |. We obtain predictions for | | using the values of the neutrino oscillation parameters, obtained in the analyzes of the presently available solar neutrino data, including the just published data from the salt phase of the SNO experiment, the atmospheric neutrino and CHOOZ data and the first data from the KamLAND experiment. The main conclusion reached in ref. [1] of the existence of significant lower bounds on | | in the cases of neutrino mass spectrum of inverted hierarchical (IH) and quasi-degenerate (QD) type is strongly reinforced by fact that combined solar neutrino data i) exclude the possibility of cos(2 θ_\odot)=0 at more than 5 s.d., ii) determine as a best fit value cos(2 θ_\odot)=0.40, and ii) imply at 95% C.L. that cos(2 θ_\odot) \geq 0.22, θ_\odot being the solar neutrino mixing angle. For the IH and QD spectra we get using, e.g., the 90% C.L. allowed ranges of values of the oscillation parameters, | | \geq 0.010 eV and | | \geq 0.043 eV, respectively. We also comment on the possibility to get information on the neutrino mass spectrum and on the CP-violation in the lepton sector due to Majorana CP-violating phases.

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arXiv2003

Neutrino Masses, Mixing and Neutrinoless Double-Beta Decay

The predictions for the effective Majorana mass | | in neutrinoless double-beta decay in the case of 3-neutrino mixing and massive Majorana neutrinos are reviewed. The physics potential of the experiments, searching for neutrinoless double-beta decay and having sensitivity to $| | \gtap 0.01$ 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 also discussed.

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arXiv2003

Precision Neutrino Oscillation Physics with an Intermediate Baseline Reactor Neutrino Experiment

We discuss the physics potential of intermediate $L \sim 20 ÷30$ km baseline experiments at reactor facilities, assuming that the solar neutrino oscillation parameters $Δm^2_{\odot}$ and $θ_{\odot}$ lie in the high-LMA solution region. We show that such an intermediate baseline reactor experiment can determine both $Δm^2_{\odot}$ and $θ_{\odot}$ with a remarkably high precision. We perform also a detailed study of the sensitivity of the indicated experiment to $Δm^2_{\rm atm}$, which drives the dominant atmospheric $ν_μ$ ($\barν_μ$) oscillations, and to $θ$ - the neutrino mixing angle limited by the data from the CHOOZ and Palo Verde experiments. We find that this experiment can improve the bounds on $\sin^2θ$. If the value of $\sin^2θ$ is large enough, $\sin^2θ\gtap 0.02$, the energy resolution of the detector is sufficiently good and if the statistics is relatively high, it can determine with extremely high precision the value of $Δm^2_{\rm atm}$. We also explore the potential of the intermediate baseline reactor neutrino experiment for determining the type of the neutrino mass spectrum, which can be with normal or inverted hierarchy. We show that the conditions under which the type of neutrino mass hierarchy can be determined are quite challenging, but are within the reach of the experiment under discussion.

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arXiv2003

On the Connection of Leptogenesis with Low Energy CP Violation and LFV Charged Lepton Decays

Assuming only a hierarchical structure of the heavy Majorana neutrino masses and of the neutrino Dirac mass matrix m_D of the see-saw mechanism, we find that in order to produce the observed baryon asymmetry of the Universe via leptogenesis, the scale of m_D should be given by the up-quark masses. Lepton flavor violating decays μ\to e + γ, τ\to μ+ γand τ\to e + γare considered and a characteristic relation between their decay rates is predicted. The effective Majorana mass in neutrinoless double beta decay depends on the CP violating phase controlling the leptogenesis if one of the heavy Majorana neutrinos is much heavier than the other two. Successful leptogenesis requires a rather mild mass hierarchy between the latter. The compatibility of this hierarchical see-saw model with the low energy neutrino mixing phenomenology requires that the mixing angle limited by the CHOOZ and Palo Verde experiments should be relatively large, \sin^2θ_3 \gtap 0.01. The CP violation effects in neutrino oscillations can be observable. In general, there is no direct connection between the latter and the CP violation in leptogenesis. If the CP violating phases of the see-saw model satisfy certain relations, the baryon asymmetry of the Universe and the rephasing invariant J_{CP} which determines the magnitude of the CP violation effects in neutrino oscillations, depend on the same CP violating phase and their signs are correlated.

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arXiv2003

Atmospheric Neutrino Oscillations, theta(13) and Neutrino Mass Hierarchy

We derive predictions for the Nadir angle (theta(n)) dependence of the ratio N(mu)/N(e) of the rates of the mu-like and e-like multi-GeV events measured in water-Cerenkov detectors 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 m2(31)| ~ (2.5 - 3.0) x 10^(-3) eV^2 >> Delta m2(21). This ratio is particularly sensitive to the Earth matter effects in the atmospheric neutrino oscillations, and thus to the values of sin^2(theta(13)) and sin^2(theta(23)), theta(13) and theta(23) 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. It is also sensitive to the type of neutrino mass spectrum which can be with normal (Delta m2(31) > 0) or with inverted (Delta m2(31) < 0) hierarchy. We show that for sin^2(theta(13)) > 0.01, sin^2(theta(23)) > 0.5 and at cos(theta(n)) > 0.4, the Earth matter effects modify substantially the theta(n)-dependence of the ratio N(mu)/N(e) and in a way which cannot be reproduced with sin^2(theta(13)) = 0 and a different value of sin^2(theta(23)). For normal hierarchy the effects can be as large as ~ 25% for cos(theta(n)) ~ (0.5 - 0.8), can reach ~ 35% in the Earth core bin cos(theta(n)) ~ (0.84 - 1.0), and might be observable. They are typically by ~ 10% smaller in the inverted hierarchy case. An observation of the Earth matter effects in the Nadir angle distribution of the ratio N(mu)/N(e) would clearly indicate that sin^2(theta(13)) > 0.01 and sin^2(theta(23)) > 0.50.

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arXiv2003

Quasi-Degenerate Neutrino Mass Spectrum, μ-> e + γDecay and Leptogenesis

In a large class of SUSY GUT models with see-saw mechanism of neutrino mass generation, lepton flavor violating (LFV) decays $μ\to e + γ$, $τ\to μ+ γ$, etc., are predicted with rates that are within the reach of present and planned experiments. A crucial element in these predictions is the matrix of neutrino Yukawa couplings $\ynu$ which can be expressed in terms of the light and RH heavy neutrino masses, the neutrino mixing PMNS matrix $U$, and an orthogonal matrix $\mathbf{R}$. Leptogenesis can take place only if $\mathbf{R}$ is complex. Considering the case of quasi-degenerate neutrinos and assuming that $\mathbf{R}$ is complex, we derive simple analytical expressions for the $μ\to e + γ$, $τ\to μ+ γ$ and $τ\to e + γ$ decay rates. Taking into account the leptogenesis constraints on the relevant parameters we show that the predicted rates of the LFV decays $μ\to e + γ$, and $τ\to e + γ$ are generically enhanced by a factor of $\sim 10^{3}$ to $\sim 10^{6}$ with respect to the rates calculated for real $\mathbf{R}$, while the $τ\to μ+ γ$ decay rate is enhanced approximately by two orders of magnitude.

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arXiv2002

On the Neutrino Mass Spectrum and Neutrinoless Double-Beta Decay

Assuming 3-nu mixing, neutrino oscillation explanation of the solar and atmospheric neutrino data and of the first KamLAND results, massive Majorana neutrinos and neutrinoless double-beta decay generated only by the (V-A) charged current weak interaction via the exchange of the three Majorana neutrinos, we analyze in detail the possibility of determining the type of the neutrino mass spectrum by measuring of the effective Majorana mass | | in neutrinoless double-beta decay. The three possible types of neutrino mass spectrum are considered: i) normal hierarchical (NH), m1 << m2 << m3, ii) inverted hierarchical (IH), m1 << m2 \simeq m3, and iii) quasi-degenerate (QD), m1 \simeq m2 \simeq m3 \geq 0.20 eV. The uncertainty in the measured value of | | due to the imprecise knowledge of the relevant nuclear matrix elements is taken into account in the analysis. We derive the ranges of values of tan^2 theta_\odot, theta_\odot being the mixing angle which controls the solar neutrino oscillations, and of the nuclear matrix element uncertainty factor, for which the measurement of | | would allow one to discriminate between the NH and IH, NH and QD and IH and QD spectra.

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arXiv2002

On the CP Violation Associated with Majorana Neutrinos and Neutrinoless Double-Beta Decay

Assuming 3-neutrino mixing and massive Majorana neutrinos, we analyze the possibility of establishing the existence of CP-violation associated with Majorana neutrinos in the lepton sector i) by measuring of the effective Majorana mass | | in neutrinoless double beta-decay with a sufficient precision and ii) by measuring of, or obtaining a stringent upper limit on, the lightest neutrino mass m1. Information on m1 can be obtained in the tritium beta decay experiment KATRIN and from astrophysical and cosmological observations. Proving that the indicated CP-violation takes place requires, in particular, a relative experimental error on the measured value of | | not bigger than 20 %, a ``theoretical uncertainty'' in the value of | | due to an imprecise knowledge of the corresponding nuclear matrix elements smaller than a factor of 2, a value of tan^2 theta_(solar) larger than 0.55, and values of the relevant Majorana CP-violating phases typically within the intervals of (Pi/2 - 3 Pi/4) and (5Pi/4 - 3Pi/2).

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arXiv2002

The SNO Solar Neutrino Data, Neutrinoless Double Beta-Decay and Neutrino Mass Spectrum

Assuming 3 neutrino mixing and massive Majorana neutrinos, we analyze the implications of the results of the solar neutrino experiments, including the latest SNO data, which favor the LMA MSW solution of the solar neutrino problem with \tan^2 θ_sol < 1, for the predictions of the effective Majorana mass | | in neutrinoless double beta decay. For \cos (2 θ_sol) \geq 0.26, which follows from the analysis of the new solar neutrino data, we find significant lower limits on | | in the cases of quasi-degenerate and inverted hierarchy neutrino mass spectrum, | | \geq 0.035 eV and | | \geq 8.5 10^-3 eV, respectively. If the spectrum is hierarchical the upper limit holds | | \leq 8.2 10^-3 eV. Correspondingly, not only a measured value of | | \neq 0, but even an experimental upper limit on | | of the order of few 10^-2 eV can provide information on the type of the neutrino mass spectrum; it can provide also a significant upper limit on the mass of the lightest neutrino m1. A measured value of | | \geq 0.2 eV, combined with data on neutrino masses from the tritium beta-decay experiment KATRIN might allow to establish whether the CP-symmetry is violated in the lepton sector.

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