Status of Neutrino Fits
I review the current status of solar, KamLAND, atmospheric and K2K neutrino experiments, implications for three-neutrino mixing and upper bounds for the neutrino masses.
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arXiv subjects
C. Giunti
Publications and source records attributed to C. Giunti.
Absolute Values of Neutrino Masses: Status and Prospects
Compelling evidences in favor of neutrino masses and mixing obtained in the last years in Super-Kamiokande, SNO, KamLAND and other neutrino experiments made the physics of massive and mixed neutrinos a frontier field of research in particle physics and astrophysics. There are many open problems in this new field. In this review we consider the problem of the absolute values of neutrino masses, which apparently is the most difficult one from the experimental point of view. We discuss the present limits and the future prospects of beta-decay neutrino mass measurements and neutrinoless double-beta decay. We consider the important problem of the calculation of nuclear matrix elements of neutrinoless double-beta decay and discuss the possibility to check the results of different model calculations of the nuclear matrix elements through their comparison with the experimental data. We discuss the upper bound of the total mass of neutrinos that was obtained recently from the data of the 2dF Galaxy Redshift Survey and other cosmological data and we discuss future prospects of the cosmological measurements of the total mass of neutrinos. We discuss also the possibility to obtain information on neutrino masses from the observation of the ultra high-energy cosmic rays (beyond the GZK cutoff). Finally, we review the main aspects of the physics of core-collapse supernovae, the limits on the absolute values of neutrino masses from the observation of SN1987A neutrinos and the future prospects of supernova neutrino detection.
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Last CPT-Invariant Hope for LSND Neutrino Oscillations
It is shown that the 99% confidence limits from the analyses of the data of cosmological and neutrino experiments imply a small marginally allowed region in the space of the neutrino oscillation parameters of 3+1 four-neutrino mixing schemes. This region can be confirmed or falsified by experiments in the near future.
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Coherence in Neutrino Interactions
The claim in hep-ph/0301231 is refuted in a pedagogical way. It is explicitly shown that extremely relativistic neutrinos produced in pion decay are correctly described by the standard flavor neutrino states which are a coherent superposition of massive neutrino states.
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Essential Solar Neutrinos
A Neutrino Unbound gem (http://www.to.infn.it/~giunti/NU). Essential information (formulas, figures, tables, references, etc.) on solar neutrinos.
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CP Violation in Bilarge Lepton Mixing
We propose a scheme of lepton mixing in which the unitary matrix that diagonalizes the neutrino mass matrix is bimaximal and the deviation from bimaximal of the lepton mixing matrix is due to the unitary matrix that diagonalizes the charged-lepton mass matrix. This matrix is assumed to be hierarchical, like the quark mixing matrix. It is shown that in general it is possible to have a sizable value for |U_{e3}| together with an effective two-neutrino maximal mixing in solar neutrino experiments. If the effective mixing in solar neutrino experiments is less than maximal, as indicated by current data, |U_{e3}| is bounded from below. Furthermore, in general the violation of CP could be relatively large.
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Current Status of Neutrino Masses and Mixings
The evidences in favor of solar and atmospheric neutrino oscillations are briefly reviewed and shown to be gracefully accommodated in the framework of three-neutrino mixing with bilarge mixing.
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Deviation of Neutrino Mixing from Bi-maximal
We have studied how observables of the neutrino mixing matrix can link up with the ones in the quark sector. The deviation from the bi-maximal flavor mixing is parameterized using a 3 x 3 unitary matrix. The neutrino mixings are investigated supposing this unitary matrix to be hierarchical like the quark mixing matrix. We obtain the remarkable prediction |U_{e3}| >= 0.03 from the experimentally allowed range tan^2 theta_{sol} = 0.24 ~ 0.89. The CP violation in neutrino oscillations is expected to be very small.
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Neutrino Wave Packets in Quantum Field Theory
We present a model of neutrino oscillations in the framework of quantum field theory in which the propagating neutrino and the particles participating to the production and detection processes are described by wave packets. The neutrino state is a superposition of massive neutrino wave packets determined by the production process, as naturally expected from causality. We show that the energies and momenta of the massive neutrino components relevant for neutrino oscillations are in general different from the average energies and momenta of the propagating massive neutrino wave packets, because of the effects of the detection process. Our results confirm the correctness of the standard expression for the oscillation length of extremely relativistic neutrinos and the existence of a coherence length.
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The Power of Confidence Intervals
We connect the power of Confidence Intervals in different Frequentist methods to their reliability. We show that in the case of a bounded parameter a biased method which near the boundary has large power in testing the parameter against larger alternatives and small power in testing the parameter against smaller alternatives is desirable. Considering the recently proposed methods with correct coverage, we show that the Maximum Likelihood Estimator method has optimal bias.
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nu_e->nu_s oscillations with large neutrino mass in NuTeV?
We propose an explanation of the NuTeV anomaly in terms of oscillations of electron neutrinos into sterile neutrinos. We derive an approximate average transition probability P(nu_e->nu_s) = 0.21 +- 0.07, which is compatible with other neutrino data if the mass-squared difference Delta m^2 that drives the oscillations is about 10 - 100 eV^2.
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The Phase of Neutrino Oscillations
Using an analogy with the well-known double-slit experiment, we show that the standard phase of neutrino oscillations is correct, refuting recent claims of a factor of two correction. We also improve the wave packet treatment of neutrino oscillations taking into account explicitly the finite coherence time of the detection process.
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Bayesian View Of Solar Neutrino Oscillations
We present the results of a Bayesian analysis of solar neutrino data in terms of nu_e->nu_{mu,tau} and nu_e->nu_s oscillations, where nu_s is a sterile neutrino. We perform a Rates Analysis of the rates of solar neutrino experiments, including the first SNO CC result, and spectral data of the CHOOZ experiment, and a Global Analysis that takes into account also the Super-Kamiokande day and night electron energy spectra. We show that the Bayesian analysis does not suffer any problem from the inclusion of the numerous bins of the CHOOZ and Super-Kamiokande energy spectra and allows to reach the same conclusions on the favored type of neutrino transitions and on the determination of the most favored values of the oscillation parameters in both the Rates and Global Analysis. Our Bayesian analysis shows that nu_e->nu_s transitions are strongly disfavored with respect to nu_e->nu_{mu,tau} transitions. In the case of nu_e->nu_{mu,tau} oscillations, the LMA region is favored by the data (86% probability), the LOW region has some small chance (13% probability), the VO region is almost excluded (1% probability) and the SMA region is practically excluded (0.01% probability). We calculate also the marginal posterior probability distributions for tan^2 theta and Delta m^2 and we show that the data imply large mixing almost with certainty and large values of Delta m^2 are favored. We present also the results of a standard least-squares analysis and we show that the standard goodness of fit test is not able to rejects pure nu_e->nu_s transitions. The likelihood ratio test allows to reject pure nu_e->nu_s transitions in favor of nu_e->nu_{mu,tau} transitions only in the Global Analysis.
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Model Independent Information On Solar Neutrino Oscillations
We present the results of a Bayesian analysis of solar neutrino data in terms of nu_e->nu_{mu,tau} oscillations, independent from the Standard Solar Model predictions for the solar neutrino fluxes. We show that such a model independent analysis allows to constraint the values of the neutrino mixing parameters in limited regions around the usual SMA, LMA, LOW and VO regions. Furthermore, there is a strong indication in favor of large neutrino mixing and large values of Delta m^2 (LMA region). We calculate also the allowed ranges of the neutrino fluxes and we show that they are in good agreement with the Standard Solar Model prediction. In particular, the ratio of the 8B flux with its Standard Solar Model prediction is constrained in the interval [0.45,1.42] with 99.73% probability. Finally, we show that the hypothesis of no neutrino oscillations is strongly disfavored in a model independent way with respect to the hypothesis of neutrino oscillations.
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Are there nu_mu or nu_tau in the flux of solar neutrinos on earth?
Using the model independent method of Villante, Fiorentini, Lisi, Fogli, Palazzo, and the rates measured in the SNO and Super-Kamiokande solar neutrino experiment, we calculate the amount of active nu_mu or nu_tau present in the flux of solar neutrinos on Earth. We show that the probability of nu_e->nu_{mu,tau} transitions is larger than zero at 99.89% CL. We find that the averaged flux of nu_{mu,tau} on Earth is larger than 0.17 times the 8B nu_e flux predicted by the BP2000 Standard Solar Model at 99% CL. We discuss also the consequences of possible nu_e->anti-nu_{mu,tau} or nu_e->anti-nu_e transitions of solar neutrinos. We derive a model-independent lower limit of 0.52 at 99% CL for the ratio of the 8B nu_e flux produced in the Sun and its value in the BP2000 Standard Solar Model.
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Quantum Mechanics of Neutrino Oscillations
Subtle problems in the theory of neutrino oscillations in vacuum are discussed. It is shown that Lorentz invariance implies that in general flavor neutrinos in oscillation experiments are superpositions of massive neutrinos with different energies and different momenta. It is argued that a wave packet description of massive neutrinos is necessary in order to understand the physics of neutrino oscillations.
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The Physical Significance of Confidence Intervals
We define some appropriate statistical quantities that indicate the physical significance (reliability) of confidence intervals in the framework of both Frequentist and Bayesian statistical theories. We consider the expectation value of the upper limit in the absence of a signal (that we propose to call "exclusion potential", instead of "sensitivity" as done by Feldman and Cousins) and its standard deviation, we define the "Pull" of a null result, expressing the reliability of an experimental upper limit, and the "upper and lower detection functions", that give information on the possible outcome of an experiment if there is a signal. We also give a new appropriate definition of "sensitivity", that quantifies the capability of an experiment to reveal the signal that is searched for at the given confidence level.
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Energy and Momentum of Oscillating Neutrinos
It is shown that Lorentz invariance implies that in general flavor neutrinos in oscillation experiments are superpositions of massive neutrinos with different energies and different momenta. It is also shown that for each process in which neutrinos are produced there is either a Lorentz frame in which all massive neutrinos have the same energy or a Lorentz frame in which all massive neutrinos have the same momentum. In the case of neutrinos produced in two-body decay processes, there is a Lorentz frame in which all massive neutrinos have the same energy.
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