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.     

A new three-flavor oscillation solution of the solar neutrino deficit in <Emphasis Type="Italic">R</Emphasis>-parity violating supersymmetry

We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the is massless and unmixed, mass and mixing being restricted to the - sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent resonance-induced - mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of eV² in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos nor CP violation in terrestrial neutrino experiments. Received: 26 December 2001 / Revised version: 16 February 2002 / Published online: 26 July 2002     

How Magnetic is the Dirac Neutrino?

We derive model-independent, "naturalness" upper bounds on the magnetic moments munu of Dirac neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of fine-tuning of effective operator coefficients, we find that current information on neutrino mass implies that[EQUATION: SEE TEXT] bohr magnetons. This bound is several orders of magnitude stronger than those obtained from analyses of solar and reactor neutrino data and astrophysical observations.     

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.     

Sterile neutrino in a minimal three-generation see-saw model

We investigate symmetries in Dirac and Majorana mass matrices of neutrinos in a three-generation scenario. We show that if we invokeL _e +L _μ-L _τ x S _2R symmetry, one combination of right-handed neutrino states remains massless which can be interpreted as a sterile neutrino. Next we consider a SU2_L x U(1)_y x U(l)_R gauge model and show how higher-dimensional operators can induce mixing between left- and right-handed states which explains solar, atmospheric and LSND experimental results.     

Nonconservation of lepton current and asymmetry of relic neutrinos

The neutrino asymmetry, \({n_v} - {n_{\bar v}}\), in the plasma of the early Universe generated both before and after the electroweak phase transition (EWPT) is calculated. It is well known that in the Standard Model the leptogenesis before the EWPT, in particular, for neutrinos, owes to the Abelian anomaly in a massless hypercharge field. At the same time, the generation of neutrino asymmetry in the Higgs phase after the EWPT has not been considered previously due to the absence of any quantum anomaly in an external electromagnetic field for such electroneutral particles as neutrinos, in contrast to the Adler anomaly for charged left- and right-handed massless electrons in the same electromagnetic field. Using the Boltzmann equation for neutrinos modified to include the Berry curvature term in momentum space, we establish a violation of the macroscopic neutrino current in the plasma after the EWPT and exactly reproduce the non-conservation of the lepton current in the symmetric phase before the EWPT that owes to the contribution of the triangle anomaly in an external hypercharge field but already without computing the corresponding Feynman diagrams. We apply the new kinetic equation to calculate the neutrino asymmetry by taking into account the Berry curvature and the electroweak interaction with plasma particles in the Higgs phase, including that after the neutrino decoupling in the absence of their collisions in the plasma. We find that this asymmetry is too small for observations. Thus, a difference between the relic neutrino and antineutrino densities, if it exists, must appear already in the symmetric phase of the early Universe before the EWPT.     

Leptonic flavor-changing Z decays in SU(2)U(1) theories with right-handed neutrinos

We analyze possible lepton-flavor-violating decays of the Z⁰ particle in a minimal extension of the standard model, in which one right-handed neutral field for each family has been introduced. Such rare leptonic decays are induced by Majorana neutrinos at the first electroweak loop level and are generally not suppressed by the ordinary “see-saw” mechanism. In particular, we find that experimental bounds on branching ratios of the order of 10⁻⁵–10⁻⁶ attainable at LEP may impose constraints on lepton-flavor-mixing parameters and the masses of the heavy Majorana neutrinos.     

Heavy fourth-generation neutrino and flavour-changing neutral currents

We study the flavour-changing neutral currents in the case that the fourth-generation neutrino exists and the known three left-handed neutrino masses are at the experimental limits of the direct measurements. The fourth-generation neutrino has the mass of order a few ten GeV and the flavour-changing processes of the heavy neutrinos are expected to be observed onZ ⁰ ine ⁺ e ^? collisions. The heavy fourth-generation neutrino is significant to reveal the nature of the neutrino; Dirac or Majorana, the see-saw mechanism and the right-handed scale.     

Dirac vs. Majorana neutrino masses from a TeV interval

We investigate the nature (Dirac vs. Majorana) and size of left-handed neutrino masses in a supersymmetric five-dimensional model compactified in the interval [0,πR], where quarks and leptons are localized on the boundaries while the gauge and Higgs sectors propagate in the bulk of the fifth dimension. Supersymmetry is broken by Scherk–Schwarz boundary conditions and electroweak breaking proceeds through radiative corrections. Right-handed neutrinos propagate in the bulk and have a general five-dimensional mass M, which localizes the zero modes towards one of the boundaries, and arbitrary boundary terms. We have found that for generic boundary terms left-handed neutrinos have Majorana masses. However for specific boundary configurations left-handed neutrinos are Dirac fermions as the theory possesses a conserved global U(1) symmetry which prevents violation of lepton number. The size of neutrino masses depends on the localization of the zero-modes of right-handed neutrinos and/or the size of the five-dimensional neutrino Yukawa couplings. Left-handed neutrinos in the sub-eV range require either MR10 or Yukawa couplings 10⁻³R, which make the five-dimensional theory perturbative up to its natural cutoff.     

Resonant spin-flavor precession constraints on the neutrino parameters and the twisting structure of the solar magnetic fields from the solar neutrino data

Resonant spin-flavor precession (RSFP) scenario with twisting solar magnetic fields has been confronted with the solar neutrino data from various ongoing experiments. The anticorrelation apparent in the Homestake solar neutrino data has been taken seriously to constrain (Δ m ² ,φ′) parameter space and the twisting profiles of the magnetic field in the convective zone of the Sun. The twisting profiles, thus derived, have been used to calculate the variation of the neutrino detection rates with the solar magnetic activity for the Homestake, Super-Kamiokande and the gallium experiments. It is found that the presence of twisting reduces the degree of anticorrelation in all the solar neutrino experiments. However, the anticorrelation in the Homestake experiment is expected to be more pronounced in this scenario. Moreover, the anticorrelation of the solar neutrino flux emerging from the southern solar hemisphere is expected to be stronger than that for the neutrinos emerging from the northern solar hemispheres.     

LETTER: Neutrino Oscillations Induced by Gravitational Recoil Effects

Quantum gravitational fluctuations of the space-time background, described by virtual D branes, may induce the neutrino oscillations if a tiny violation of the Lorentz invariance (or a violation of the equivalence principle) is required. In this approach, the oscillation length of massless neutrinos turns out to be proportional to E ^–2 M, where E is the neutrino energy and M is the mass scale characterizing the topological fluctuations in the vacuum. Such a functional dependence on the energy is the same obtained in the framework of loop quantum gravity.     

Single field baryogenesis

We propose a new variant of the Affleck-Dine baryogenesis mechanism in which a rolling scalar field couples directly to left- and right-handed neutrinos, generating a Dirac mass term through neutrino Yukawa interactions. In this setup, there are no explicitly CP violating couplings in the Lagrangian. The rolling scalar field is also taken to be uncharged under the B - L quantum numbers. During the phase of rolling, scalar field decays generate a nonvanishing number density of left-handed neutrinos, which then induce a net baryon number density via electroweak sphaleron transitions.     

Dirac neutrinos in superstring models with an intermediate scale

We discuss neutrino masses in superstring-inspired models. We present a model possessing an intermediate scale ∼ 10⁸–10⁹ GeV which gives rise to Dirac neutrinos with masses in a range that can account both for the dark matter and the solar neutrino puzzle through the MSW effect. It also accounts for the observed baryon asymmetry through the out-of-equilibrium decay of heavy colored fields at temperatures close to the electroweak scale. Although baryon- and lepton-number symmetries are explicitly broken there are no observable low-energy baryon- or lepton-number-violating effects due to the presence of an accidental unbroken global U(1)_2B−L symmetry.     

Vacuum solutions of neutrino anomalies through a softly broken U(1) symmetry

We discuss an extended model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino anomalies in terms of the vacuum oscillations of the three known neutrinos. The model uses a softly broken –– symmetry and contains a heavy scale GeV. The –– symmetric neutrino masses solve the atmospheric neutrino anomaly while breaking of –– generates the highly suppressed radiative mass scale needed for the vacuum solution of the solar neutrino problem. All the neutrino masses in the model are inversely related to , thus providing seesaw-type of masses without invoking any heavy right-handed neutrinos. The possible embedding of the model into an SU(5) grand unified theory is discussed. Received: 5 August 1999 / Revised version: 18 November 1999 / Published online: 6 April 2000     

Magnetic moments of Dirac and Majorana neutrinos

We present two models where the magnetic moment of the electron neutrino can be as high as the experimental bound of 10⁻¹⁰ Bohr magnetons. The models, one in which the neutrinos are Dirac particles and the other where they are Majorana particles possessing transition moments, are consistent with known experiments and are realizations of a recent suggestion by Voloshin, Vysotsky and Okun to explain the solar neutrino experiment.     

The νMSM,inflation, and dark matter

We show how to enlarge the νMSM (the minimal extension of the Standard Model by three right-handed neutrinos) to incorporate inflation and provide a common source for electroweak symmetry breaking and for right-handed neutrino masses. In addition to inflation, the resulting theory can explain simultaneously dark matter and the baryon asymmetry of the Universe; it is consistent with experiments on neutrino oscillations and with all astrophysical and cosmological constraints on sterile neutrino as a dark matter candidate. The mass of inflaton can be much smaller than the electroweak scale.     

Neutrino flavor conversion in random magnetic fields

If massive neutrinos possess magnetic moments, a magnetic field can cause a spin flip. In the case of Dirac neutrinos the spin flip converts an active neutrino into a sterile one and vice versa. By constrast, if neutrinos are Majorana particles, a spin flip converts them to a neutrino of a different flavor. We examine the behavior of neutrinos in a random magnetic field as it occurs, for instance, in certain astronomical objects, such as an active galactic nucleus. Both Dirac and Majorana neutrinos behave ergodically: independently of their initial density matrix, they tend towards an equipartition of the helicity states. As a result, about half of the Dirac neutrinos produced becomes sterile. For Majorana neutrinos, there will be an approximate equipartition of flavors, independently of the production mechanism.     

Leptonic CP-violation and mirror leptons

We study leptonic CP-violation within a single fermion generation in an extended electro-weak model where new right-handed leptons, so-called mirror leptons, exist and mix with standard left-handed leptons. Essential differences are pointed out between the mixing of a left-handed neutrino with a mirror neutrino in such a model and the ordinary mixing of two left-handed neutrinos in the standard model. E.g. in the mirror case CP-violation may occur even if neutrinos are Dirac particles. The number of physical CP-violation phases is determined for different mixing schemes and parameterizations of the leptonic weak currents in terms of these phases are presented.     

The Solar Neutrino Problem as Evidence of New Interaction

A new concept to solve the solar neutrino problem that is based on the hypothesis about the existence of a new interaction of electron neutrinos with nucleons mediated by massless pseudoscalar bosons is proposed. At each collision of a neutrino with nucleons of the Sun, its helicity changes from left- to right-handed and vice versa, and its energy decreases. The postulated hypothesis, having only one free parameter, provides good agreement between the calculated and experimental characteristics of all five observed processes with solar neutrinos.     

Testing the vacuum oscillation and the MSW solutions of the solar neutrino problem

Solar model independent tests of the vacuum oscillation and MSW solutions of the solar neutrino problem are considered. Detailed predictions for time (seasonal) variations of the signals due to neutrino oscillations in vacuum are given for the future solar neutrino detectors (SNO, Super-Kamiokande, BOREXINO, HELLAZ). Results on the distortions of the spectra of ⁸B neutrinos, and of e⁻ from the reaction ν + e⁻ → ν + e⁻ induced by ⁸B neutrinos, are presented in the cases of vacuum oscillations or MSW transitions for a large number of values of the relevant parameters. The possibilities to distinguish between the vacuum oscillation, the MSW adiabatic, and the MSW nonadiabatic transitions in the future solar neutrino experiments are discussed.