Spin flip of neutrinos with magnetic moment in core-collapse supernova

Neutrinos with magnetic moment experience chirality flips while scattering off charged particles. It is known that if neutrino is a Dirac fermion, then such chirality flips lead to the production of sterile right-handed neutrinos inside the core of a star during the stellar collapse, which may facilitate the supernova explosion and modify the supernova neutrino signal. In the present paper we reexamine the production of right-handed neutrinos during the collapse using a dynamical model of the collapse. We refine the estimates of the values of the Dirac magnetic moment which are necessary to substantially alter the supernova dynamics and neutrno signal. It is argued in particular that Super-Kamiokande will be sensitive at least to μ _{ν Dirac} = 10⁻¹³μ_B in case of a galactic supernova explosion. Also we briefly discuss the case of Majorana neutrino magnetic moment. It is pointed out that in the inner supernova core spin flips may quickly equilibrate electron neutrinos with nonelectron antineutrinos if μ _{ν Majorana} ≳ 10⁻¹²μ_B. This may lead to various consequences for supernova physics.     

Weak neutral currents in the U3(W)-gauge theory of weak and electromagnetic interactions

A discussion is given of the implications of the recently proposed U₃(W)-gauge theory of weak and electromagnetic interactions (Pandit 1976) for some phenomena resulting from its weak neutral currents: (1) neutrino-electron scattering, (2) neutrino-nucleon elastic and inelastic scattering, (3) coherent neutrino-nucleus scattering (4) weak interaction effects ine ⁺ e ⁻→μ⁺μ⁻ and (5) parity-violation in atomic physics. The theory agrees quite well with the available experimental results on neutrino processes. We find the coherent neutrino-nucleus cross-section for Fe⁵⁶ to be about 6 times larger than that in the WS-GIM theory giving some hope of accounting for supernova explosion by the resulting neutrino-radiation pressure.     

On the possible existence of a neutrino pulsar

If the neutrino has a magnetic moment in the interval 10⁻¹³μ_B < μ _ν < 10⁻¹² μ_B and if a magnetic field of strength about 10¹⁴ G exists in the supernova envelope, the effect of a pulsation of a neutrino signal from a supernova may arise owing to a ν _L → ν _R resonance transition in the envelope magnetic field.     

Anomalouse + e − pairs in heavy ion collisions and solar neutrinos

The production of anomalouse ⁺ e ^–pairs in heavy ion collisions and the solar neutrino puzzle are two seemingly unrelated problems of the standard model of electroweak interactions. According to the observations made at Homestake and Kamiokande, the flux of solar neutrinos is too small. Furthermore, the observations made at Homestake (neutrino-nucleon scattering) show anticorrelation of the solar neutrino flux with sunspots, unlike the observations made in Kamiokande (neutrino-electron scattering). According to the previously proposed model inspired by T(opological) G(eometro) D(ynamics), anomalouse ⁺ e ^–pairs result from the decay of the leptopion, which can be regarded as a bound state of color excited electrons. In this paper we show that the generalization of PCAC ideas leads to a prediction for the lifetime and production cross section of the leptopion in agreement with data. The model is also consistent with constraints coming from Babbha scattering and supernova physics. Leptopion exchange implies a new weak interaction between leptons at low cm energies (of the order of a few MeVs), which explains the Kamiokande-Homestake puzzle. Part of the solar neutrinos are transformed in the convective zone of the Sun to right-handed neutrinos inert with respect to ordinary electroweak interactions, but interacting with electrons via leptopion exchange so that they are observed in Kamiokande. A correct average value for the neutrino flux at Kamiokande is predicted using as input the Homestake flux, and the anticorrelation with sunspots in Kamiokande is predicted to be considerably weaker than in Homestake.     

The Baikal Neutrino Experiment: Status and beyond

The present status of the Baikal Neutrino Experiment and the present results of a search for upward going atmospheric neutrinos, WIMPs, and magnetic monopoles obtained with the NT-200 detector are reviewed. The results of a search for very high-energy neutrinos are presented as well. An upper limit on the ν _e +ν _e +ν _τ neutrino diffuse flux of E ²Φ(E)<1.3×10⁻⁶ cm⁻² s⁻¹ sr⁻¹ GeV within a neutrino energy range of 10⁴–10⁷ GeV is obtained, assumingan E ⁻² behavior of the neutrino spectrum and a flavor ratio ν _e :ν _π :ν _τ =1:1:1. We also describe the moderate upgrade of the NT-200 planned for the next few years and present a possible detector on the Gigaton scale. From Yadernaya Fizika, Vol. 67, No. 6, 2004, pp. 1186–1194. Original English Text Copyright ? 2004 by Aynutdinov, Balkanov, Belolaptikov, Bezrukov, Budnev, Chensky, Chernov, Danilchenko, Dzhilkibaev, Domogatsky, Dyachok, Gaponenko, O. Gress, T. Gress, Klabukov, Klimov, Klimushin, Konischev, Koshechkin, Kulepov, Kuzmichev, Kuznetzov, Lubsandorzhiev, Mikheyev, Milenin, Mirgazov, Moiseiko, Osipova, Panfilov, G. Pan'kov, L. Pan'kov, Parfenov, Pavlov, Pliskovsky, Pokhil, Polecshuk, Popova, Prosin, Rosanov, Rubtzov, Semeney, Shaibonov, Spiering, Streicher, Tarashansky, Vasiliev, Vyatchin, Wischnewski, Yashin, Zhukov. This article was submitted by the authors in English.     

Plasma-induced neutrino helicity flip in a supernova core and a constraint on the Dirac neutrino magnetic moment

We investigate the neutrino helicity flip under supernova core conditions, where the left-handed neutrinos being produced can be converted into right-handed neutrinos sterile with respect to weak interactions owing to the interaction of the magnetic moments with plasma electrons and protons. In calculating the probability for the conversion neutrino scattering by plasma components, we take into account the polarization effects attributable to both electrons and protons in the photon propagator. Based on realistic models with radial distributions and time evolution of physical parameters in a supernova core, we have obtained upper limits on the Dirac neutrino magnetic moment averaged over flavors and time from the condition that the influence of the right-handed neutrino emission on the total cooling time scale should be limited.     

Inverted hierarchy of neutrino masses disfavored by supernova 1987A

We discuss the flavor conversion of supernova neutrinos in the three-flavor mixing scheme of neutrinos. We point out that by neutrino observation from supernova one can discriminate the inverted hierarchy of neutrino masses from the normal one if s₁₃²≳a few×10⁻⁴, irrespective of which oscillation solution to the solar neutrino problem is realized in nature. We perform an analysis of data of SN1987A and obtain a strong indication that the inverted mass hierarchy is disfavored unless s₁₃²≲a few×10⁻⁴.     

Heavy sterile neutrinos and supernova explosions

We consider sterile neutrinos with rest masses 0.2 GeV and with vacuum flavor mixing angles θ²>10⁻⁸ for mixing with τ-neutrinos, or 10⁻⁸<θ²<10⁻⁷ for mixing with muon neutrinos. Such sterile neutrinos could augment core collapse supernova shock energies by enhancing energy transport from the core to the vicinity of the shock front. The decay of these neutrinos could produce a flux of very energetic active neutrinos, detectable by future neutrino observations from galactic supernova. The relevant range of sterile neutrino masses and mixing angles can be probed in future laboratory experiments.     

Gemma experiment: Three years of the search for the neutrino magnetic moment

The result of the 3-year neutrino magnetic moment measurement at the Kalinin Nuclear Power Plant (KNPP) with the GEMMA spectrometer is presented. Antineutrino-electron scattering is investigated. A high-purity germanium detector of 1.5 kg placed at a distance of 13.9 m from the 3 GW_th reactor core is exposed to the antineutrino flux of 2.7 × 10¹³ cm⁻² s⁻¹. The scattered electron spectra taken in (5184 + 6798) and (1853 + 1021) h for the reactor ON and OFF periods are compared. The upper limit for the neutrino magnetic moment μ_v < 3.2 × 10⁻¹¹μ _B at 90% CL is derived from the data processing.     

Search for νμ and ντ supernova neutrinos with massive liquid-scintillation detectors

Summary In this paper we have estimated the sensitivity of a large-mass liquid-scintillation detector to search for supernova neutrinos of different flavours. Events produced by ν_μ and ν_τ interactions can be identified by looking at the distorsion in the neutrino energy spectrum. We have shown here that, overlapped to the main energy distribution produced by interactions with protons a peak at 15.11 MeV (due to the de-excitation of¹²C^* nuclei excited by neutral-current neutrino interactions) gives a possible signature of these neutrino flavours. Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction.     

Quasi-elastic neutrino-nucleus reactions

The quasi-elastic contribution of the nuclear inclusive electron scattering model developed in [A. Gil, J. Nieves, and E. Oset: Nucl. Phys. A 627 (1997) 543] is extended to the study of electroweak charged current induced nuclear reactions at intermediate energies of interest for future neutrino oscillation experiments. The model accounts for long-range nuclear (RPA) correlations, final state interaction and Coulomb corrections. RPA correlations are shown to play a crucial role in the whole range of neutrino energies, up to 500 MeV, studied in this work. Predictions for inclusive muon capture for different nuclei, and for the reactions ¹²C(ν _μ , μ ₋)X and ¹²C(ν _e, e⁻)X near threshold are also given. Presented by M. Valverde at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

Matter effects for solar neutrino oscillations

Possible solar neutrino oscillations are reviewed in the two-neutrino case taking into account the effect of coherent forward scattering when neutrinos travel through the sun and earth. As recently pointed out by Mikheyev and Smirnov this effect can induce a large suppression of the solar ν_e flux for values of Δm ² around 10^?4–10^?8 eV² even for small values of the mixing angle. It also may cause substantial modifications of the solar neutrino spectrum shape. All this may be used for determining Δm ² and sin² 2θ in a large domain from the experimental results of the chlorine, gallium, indium and heavy water detectors.     

Neutrino mixing and masses in a left–right model with mirror fermions

In the framework of a left–right model containing mirror fermions with gauge group SU(3) _C ⊗SU(2) _L ⊗SU(2) _R ⊗U(1) _Y′, we estimate the neutrino masses, which are found to be consistent with their experimental bounds and hierarchy. We evaluate the decay rates of the Lepton Flavor Violation (LFV) processes μ→eγ, τ→μγ and τ→eγ. We obtain upper limits for the flavor-changing branching ratios in agreement with their present experimental bounds. We also estimate the decay rates of heavy Majorana neutrinos in the channels N→W ^± l ^∓, N→Zν _l and N→Hν _l , which are roughly equal for large values of the heavy neutrino mass. Starting from the most general Majorana neutrino mass matrix, the smallness of active neutrino masses turns out from the interplay of the hierarchy of the involved scales and the double application of seesaw mechanism. An appropriate parameterization on the structure of the neutrino mass matrix imposing a symmetric mixing of electron neutrino with muon and tau neutrinos leads to tri-bimaximal mixing matrix for light neutrinos.     

A lithium experiment in the program of solar neutrino research

Experiments sensitive to pp neutrinos from the Sun are very promising for precise measurement of the mixing angle ϑ ₁₂. A νe ⁻ scattering experiment (XMASS) and/or a charged-current experiment (indium detector) can measure the flux of electron pp neutrinos. One can find the total flux of pp neutrinos from a luminosity constraint after the contributions of ⁷Be and CNO neutrinos to the total luminosity of the Sun are measured. A radiochemical experiment utilizing a lithium target has high sensitivity to the CNO neutrinos; thus, it has a good promise for precise measurement of the mixing angle and for a test of the current theory of evolution of the stars. The text was submitted by the authors in English.     

Mimicking diffuse supernova antineutrinos with the sun as a source

Measuring the $ \bar \nu _e $ \bar \nu _e component of the cosmic diffuse supernova neutrino background (DSNB) is the next ambitious goal for low-energy neutrino astronomy. The largest flux is expected in the lowest accessible energy bin. However, for E ≲ 15 MeV a possible signal can be mimicked by a solar $ \bar \nu _e $ \bar \nu _e flux that originates from the usual ⁸B neutrinos by spin-flavor oscillations. We show that such an interpretation is possible within the allowed range of neutrino electromagnetic transition moments and solar turbulent field strengths and distributions. Therefore, an unambiguous detection of the DSNB requires a significant number of events at E ≳ 15 MeV.     

Majorana neutrino masses in the three-flavor Pauli model

A special Majorana model for three neutrino flavors is developed on the basis of the Pauli transformation group. In this model, the neutrinos possess a partially conserved generalized lepton (Pauli) charge that makes it possible to discriminate between neutrinos of different type. It is shown that, within the model in question, a transition from the basic “mass” representation, where the average value of this charge is zero, to the representation associated with physical neutrinos characterized by specific Pauli “flavor” charges establishes a relation between the neutrino mixing angles θ _{mix, 12}, θ _{mix, 23}, and θ _{mix, 13} and an additional relation between the Majorana neutrino masses. The Lagrangian mass part, which includes a term invariant under Pauli transformations and a representation-dependent term, concurrently assumes a “quasi-Dirac” form. With allowance for these relations, the existing set of experimental data on the features of neutrino oscillations makes it possible to obtain quantitative estimates for the absolute values of the neutrino masses and the 2β-decay mass parameter m _ββ and a number of additional constraints on the neutrino mixing angles.     

Coincidences among the data recorded by the baksan, kamioka and mont blanc underground neutrino detectors, and by the Maryland and Rome gravitational-wave detectors during Supernova 1987 A

Summary The data recorded with the neutrino detectors at Mont Blanc, Kamioka, Baksan and with the gravitational-wave detectors in Maryland and Rome have been analysed searching for correlations associated with SN 1987 A, without presuming or excluding hypotheses for correlations due to neutrinos and gravitational waves. The statistical analysis has been based on a previous analysis that showed a correlation among Maryland, Rome and Mont Blanc with a probability to be accidental less than 10⁻⁵. Independent correlations are found during a period of one or two hours, around the Mont Blanc 5ν burst (2h 52 min 36 s UT), among the various sets of data: Mont Blanc-Baksan with a probability to be accidental of the order ofp∼4·10⁻³, Mont Blanc-Kamioka withp∼4·10⁻³, Maryland-Rome-Kamioka withp∼5·10⁻⁴, Maryland-Rome-Baksan withp∼5·10⁻². It is remarkable that the events from all the neutrino detectors follow the signals from the g.w. detectors by a time of the order of 1/2 or 1 s. At present we will not give a physical interpretation of the observed correlations which have strong statistical significance. Professor Edoardo Amaldi died on December 5, 1989.     

μ → <Emphasis Type="Italic">e</Emphasis>γ decay versus the μ → <Emphasis Type="Italic">eee</Emphasis> bound and lepton flavor violating processes in supernova

Even tiny lepton flavor violation (LFV) due to some New Physics is able to alter the conditions inside a collapsing supernova core and probably to facilitate the explosion. LFV emerges naturally in a see-saw type-II model of neutrino mass generation. Experimentally, the LFV beyond the Standard Model is constrained by rare lepton decay searches. In particular, strong bounds are imposed on the μ → eee branching ratio and on the μ-e conversion in muonic gold. Currently, the μ→eγ is under investigation in the MEG experiment that aims at a dramatic increase in sensitivity in the next three years. We seek a see-saw type-II LFV pattern that fits all the experimental constraints, leads to Br(μ →eγ) ≳ Br(μμ →eee), and ensures a rate of LFV processes in supernova high enough to modify the supernova physics. These requirements are sufficient to eliminate almost all freedom in the model. In particular, they lead to the prediction 0.4 × 10⁻¹² ≲ Br(μ → eγ) ≲ 6 × 10⁻¹², which will be testable by MEG in the nearest future. The considered scenario also constrains the neutrino mass-mixing pattern and provides lower and upper bounds on τ-lepton LFV decays. We also briefly discuss a model with a single bilepton in which the μ → eee decay is absent at the tree level.     

Transition radiation by neutrinos

We calculate the transition radiation process ν→νγ at an interface of two media. The neutrinos are taken to be with only standard-model couplings. The medium fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation. The transition radiation occurs when at least one of those quantities have different values in different media. The neutrino mass is ignored due to its negligible contribution. We present a result for the probability of the transition radiation which is both accurate and analytic. For Eν=1 MeV neutrino crossing polyethylene-vacuum interface the transition radiation probability is about ¹⁰−39 and the energy intensity is about ¹⁰−34 eV. At the surface of the neutron stars the transition radiation probability may be ∼¹⁰−20. Our result is by the three orders of magnitude larger than those of previous calculations.     

Nuclear responses for neutrinos and neutrino studies by double beta decays and inverse beta decays

This is a brief report on recent studies of nuclear responses for neutrinos (v) by charge exchange reactions, v masses by double beta (ββ) decays and of solar and supernova v’s by inverse β decays. Subjects discussed include (1) v studies in nuclear micro-laboratories, (2) v masses studied by ββ decays of ¹⁰⁰Mo and nuclear responses for ββ — v, (3) solar and supernova v’s by inverse β decays and v responses for ⁷¹Ga and ¹⁰⁰Mo, and (4) MOON (molybdenum observatory of neutrinos) for spectroscopic studies of Majorana v masses with sensitivity of m _v ∼ 0.03 eV by ββ decays of ¹⁰⁰Mo and real-time studies of low energy solar and supernova v’s by inverse β decays of ¹⁰⁰Mo.