Neutrino Transition Research Articles

Transition magnetic moments and collective neutrino oscillations: three-flavor effects and detectability

We demonstrate the non-negligible effect of transition magnetic moments on three-flavor collective oscillations of Majorana neutrinos in the core of type-II supernovae, within the single-angle approximation. We argue that data from a galactic supernova in conjunction with terrestrial experiments can potentially give us clues about the non-zero nature of neutrino transition magnetic moments if these are Majorana fermions, even if their values are as small as those predicted by the Standard Model augmented by nonzero neutrino Majorana masses.

Muon neutrino to electron neutrino oscillations in the MINOS experiment

MINOS is a long-baseline neutrino oscillation experiment situated along Fermilabʼs high-intensity NuMI neutrino beam. MINOS has completed an updated search for muon neutrino to electron neutrino transitions, observation of which would indicate a non-zero value for the neutrino mixing angle θ13. The present 7×1020 protons-on-target data set represents more than double the exposure used in the previous analysis. The new results are presented.

Ga source experiment for detection of short baseline neutrino oscillations

The status of the feasibility studies for a proposed Ga source experiment to search for possible electron neutrino transitions into sterile states is presented. The advantages of the proposed technique are considered. The experiment has the potential to detect neutrino oscillation transitions with mass-squared difference Δm2 > 0.5 eV2 with a sensitivity to disappearance of electron neutrinos of a few percent

Constraining anR-parity violating supergravity model with the Higgs-induced Majorana neutrino magnetic moments

It is well known that $R$-parity violating supersymmetric models predict a nonzero magnetic moment for neutrinos. In this work we study the Majorana neutrino transition magnetic moments within an RpV modified minimal supergravity model. Specifically, we discuss the contributions coming from the charged Higgs bosons, Higgsinos, leptons, sleptons, charged gauge bosons, and charginos. We use the experimental results from the MUNU Collaboration to restrict the model's parameter space. A comparison with two other types of contributions (only trilinear RpV couplings and trilinear plus neutrino-neutralino mixing) is also presented. We have found that the presently discussed processes dominate significantly, exceeding in some cases even the experimental limits.

Investigation of neutrino oscillations in the T2k long-baseline accelerator experiment

High-sensitivity searches for transitions of muon neutrinos to electron neutrinos are the main task of the T2K (Tokai-to-Kamioka) second-generation long-baseline accelerator neutrino experiment. The present article is devoted to describing basic principles of T2K, surveying experimental apparatuses that it includes, and considering in detail the muon-range detector (SMRD) designed and manufactured by a group of physicists from the Institute of Nuclear Research (Russian Academy of Sciences, Moscow). The results of the first measurements with a neutrino beam are presented, and plans for the near future are discussed.

Expressions for Neutrino Wave Functions and Transition Probabilities at Three Neutrino Oscillations in Vacuum and Some of Their Applications

We have considered three neutrino transitions and oscillations in the general case and obtained expressions for neutrino wave functions in three cases: with CP violation, without CP violations and the case when $\nu_e \leftrightarrow \nu_\tau$ transitions are absent (some works indicate on this possibility). Then using the existing experimental data some analysis has been fulfilled. This analysis definitely has shown that transitions $\nu_e \leftrightarrow \nu_\tau$ cannot be closed for the Solar neutrinos. However, this possibility may be realized by using the mechanism of resonance enhancement neutrino oscillations in matter (the Sun). But this possibility is not confirmed by the Solar neutrinos spectrum (the Solar neutrinos spectrum is not distorted) and the Day-Night effect (this effect is not observed). It was found out that the probability of $\nu_e \leftrightarrow \nu_e$ neutrino transitions is positive defined value only if the angle of $\nu_e, \nu_\tau$ mixing $\beta \le 15^o \div 17^o$.

MSW Oscillations – LMA and Subdominant Effects

These notes, based on a talk given at the Neutrino 2006 conference [Neutrino 2006, Santa Fe, New Mexico, USA, http://neutrinosantafe06.com/ ], review the sensitivity of solar neutrinos to certain types of new physics, namely modifications of neutrino-matter interactions by the exchange of a new heavy particle and a large neutrino transition moment. Both were first proposed in the 1970ʼs as possible explanations for the solar neutrino “problem” and were actively investigated for many years. While since ruled out as the dominant mechanisms of the solar neutrino flavor conversion, they remain of great interest as subdominant effects, which, if observed, would open a window to new physics. We outline the sensitivity of the current experiments and describe progress that may be expected in the near future.

Neutrino oscillations and uncertainty relations

We show that coherent flavor neutrino states are produced (and detected) due to the momentum-coordinate Heisenberg uncertainty relation. The Mandelstam–Tamm time–energy uncertainty relation requires non-stationary neutrino states for oscillations to happen and determines the time interval (propagation length) which is necessary for that. We compare different approaches to neutrino oscillations which are based on different physical assumptions but lead to the same expression for the neutrino transition probability in standard neutrino oscillation experiments. We show that a Mössbauer neutrino experiment could allow us to distinguish different approaches and we present arguments in favor of the 163Ho–163Dy system for such an experiment.

Rephasing invariance and the neutrinoμ−τsymmetry

The vacuum neutrino mixing is known to exhibit an approximate $\mu-\tau$ symmetry, which was shown to be preserved for neutrino propagating in matter. This symmetry reduces the neutrino transition probabilities to very simple forms when expressed in a rephasing invariant parametrization introduced earlier. Applications to long baseline experiments are discussed.

Turbulence effects on supernova neutrinos

Multidimensional core-collapse supernova simulations exhibit turbulence of large amplitude and over large scales. As neutrinos pass through the supernova mantle the turbulence is expected to modify their evolution compared to the case where the explosion is free of turbulence. In this paper we study this turbulence effect upon the neutrinos modeling the turbulence expected from multidimensional simulations by adding matter density fluctuations to density profiles taken from one-dimensional hydrodynamical simulations. We investigate the impact upon the supernova neutrino transition probabilities as a function of the neutrino mixing angle ${\ensuremath{\theta}}_{13}$ and turbulence amplitude. In the high resonant channel and with large ${\ensuremath{\theta}}_{13}$ values we find that turbulence is effectively two flavor for fluctuation amplitudes $\ensuremath{\lesssim}1%$ and have identified a new effect due to the combination of turbulence and multiple high resonances that leads to a sensitivity to fluctuations amplitudes as small as $\ensuremath{\sim}0.001%$. At small values of ${\ensuremath{\theta}}_{13}$, beyond the range achievable in Earth based experiments, we find that turbulence leads to new flavor transient effects in the channel where the Mikheev-Smirnov-Wolfenstein high resonance occurs. Finally, we investigate large amplitude fluctuations which lead to three-flavor effects due to broken high-low factorization and significant nonresonant transitions and identify two nonresonant turbulence effects, one depending on the ${\ensuremath{\theta}}_{13}$, and the other independent of this angle and due to the low Mikheev-Smirnov-Wolfenstein resonance.

0ν2β NUCLEAR MATRIX ELEMENTS AND NEUTRINO MAGNETIC MOMENTS

We compare different methods of obtaining the neutrinoless double beta decay nuclear matrix elements (NME). On the example of 76 Ge we use the NME to calculate the Majorana neutrino transition magnetic moments, generated through particle–sparticle R-parity violating loop diagrams whithin the minimal supersymmetric standard model.

Neutrino self-energy in an external magnetic field

Using the exact propagators in a constant magnetic field, the neutrino self-energy has been calculated to all orders in the field strength B within the minimal extension of the Weinberg-Salam model with massive Dirac neutrinos. A simple and very accurate formula for the self-energy is obtained, that is valid for 0{<=}B<<m{sub W}{sup 2}/e and for neutrino transverse momentum to the magnetic field p{sub perpendicular}<<m{sub W}. I discuss the implications of this finding to the dispersion of massless neutrinos in vacuum and in a charge-symmetric medium, and to the magnetic field induced resonance transitions of massive neutrinos inside supernovae and magnetars, and calculate the neutrino magnetic moment.

Interaction of Dirac and Majorana neutrinos with weak gravitational fields

In this paper the interaction of high energy neutrinos with weak gravitational fields is briefly explored. The form of the graviton-neutrino vertex is motivated from Lorentz and gauge invariance and the nonrelativistic interpretations of the neutrino-gravitational form factors are obtained. We comment on the renormalization conditions, the preservation of the weak equivalence principle and the definition of the neutrino mass radius. We associate the neutrino-gravitational form factors with specific angular momentum states. Based on Feynman diagrams, spin-statistics, $CP$ invariance and symmetries of the angular momentum states in the graviton-neutrino vertex, we deduce differences between the Majorana and Dirac cases. It is then proved that in spite of the theoretical differences between the two cases, as far as experiments are considered, they would be virtually indistinguishable for any space-time geometry satisfying the weak-field condition. We then calculate the transition gravitational form factors for the neutrino by evaluating the relevant Feynman diagrams at 1-loop and estimate a neutrino transition mass radius. The form factor is seen to depend on the momentum transfer very weakly. It is also seen that the neutrino transition mass radius is smaller than the typical neutrino charge radius by a couple of orders of magnitude.

Solar Neutrino Variability and Its Implications for Solar Physics and Neutrino Physics

Recent coordinated power-spectrum analyses of radiochemical solar neutrino data and the solar irradiance have revealed a highly significant, high-Q common modulation at 11.85 yr−1. Since the stability of this frequency points to an explanation in terms of rotation, this result may be attributable to non-spherically-symmetric nuclear burning in a solar core with sidereal rotation frequency 12.85 yr−1. The variability of the amplitude (on a timescale of years) suggests that the relevant nuclear burning is variable as well as asymmetric. Recent analysis of Super-Kamiokande solar neutrino data has revealed r-mode-type modulations with frequencies corresponding to a region with sidereal rotation frequency 13.97 yr−1. If this modulation is attributed to the RSFP (resonant spin flavor precession) process, it provides a measurement of the rotation rate deep in the radiative zone. These two results suggest that the core rotates significantly more slowly than the radiative zone. If one accepts an upper limit of 7 MG for the Sun's internal magnetic field, an RSFP interpretation of the Super-Kamiokande results leads to a lower limit of 10−12 Bohr magnetons for the neutrino transition magnetic moment.

Constraining bilinearR-parity violation from neutrino masses

We confront the R-parity violating MSSM model with the neutrino oscillation data. Investigating the 1-loop particle-sparticle diagrams with additional bilinear insertions on the external neutrino lines we construct the relevant contributions to the neutrino mass matrix. A comparison of the so-obtained matrices with the experimental ones assuming normal or inverted hierarchy and taking into account possible CP violating phases, allows to set constraints on the values of the bilinear coupling constants. A similar calculation is presented with the input from the Heidelberg-Moscow neutrinoless double beta decay experiment. We base our analysis on the renormalization group evolution of the MSSM parameters which are unified at the GUT scale. Using the obtained bounds we calculate the contributions to the Majorana neutrino transition magnetic moments.

Self-induced neutrino transitions in supernovae

We studied supernova neutrino oscillations in the presence of self-interactions that induce collective flavor transitions. For the chosen matter profile, collective transitions are decoupled from matter oscillations, allowing for the analytical interpretation of the numerical simulations. Of particular interest is the case of inverted neutrino hierarchy, where neutrino propagation can be divided in three regimes, of synchronized and bipolar oscillations, and then of spectral split. Our simulation shows that averaging over neutrino trajectories does not alter the nature of these three regimes, apart from the smearing of fine structure details.

Remarks to the standard scheme (theory) of neutrino oscillations. Corrected scheme of neutrino oscillations

In the standard theory of neutrino oscillations, it is supposed that physically observed neutrino states ν e , νμ, ντ, have no definite masses, that they are initially produced as a mixture of the ν1, ν2, ν3 neutrino states (i.e., they are produced as a wave packet), and that neutrino oscillations are the real ones. Then, this wave packet must decompose at a definite distance into constituent parts and neutrino oscillations must disappear. It was shown that these suppositions lead to violation of the law of energy and momentum conservation. An alternative scheme of neutrino oscillations obtained within the framework of particle physics has been considered, where the above mentioned shortcomings are absent, the oscillations of neutrinos with equal masses are the real ones, and the oscillations of neutrinos with different masses are the virtual ones. Expressions for probabilities of neutrino transitions (oscillations) in the alternative (corrected) scheme are given.

Spin-flavor oscillations of neutrinos in rapidly varying external fields

Spin-flavor oscillations of neutrinos in rapidly varying external fields are studied. A method for describing neutrino oscillations in arbitrary rapidly varying external fields is developed. An effective Hamiltonian that describes the evolution of the averaged neutrino wave function is obtained. Neutrino oscillations in rapidly varying magnetic fields are considered on the basis of the general formalism developed in this study. Neutrino transitions in a superposition of a constant and a rotating (in space) magnetic field that are transverse with respect to the neutrino velocity are studied. The probabilities of transitions in spin-flavor oscillations of neutrinos in the magnetic fields of the Sun are estimated. Numerical solutions to the Schrodinger equation for the Hamiltonian that describes neutrino interaction with a constant and a rotating (in space) magnetic field are given. It is shown that the approximate analytic formula obtained in the present study for the probability of neutrino transitions is consistent with the respective numerical solution to the evolution equation at high frequencies of the rotating magnetic fields.

Lightest sterile neutrino abundance within theνMSM

We determine the abundance of the lightest (dark matter) sterile neutrinos created in the Early Universe due to active-sterile neutrino transitions from the thermal plasma. Our starting point is the field-theoretic formula for the sterile neutrino production rate, derived in our previous work [JHEP 06(2006)053], which allows to systematically incorporate all relevant effects, and also to analyse various hadronic uncertainties. Our numerical results differ moderately from previous computations in the literature, and lead to an absolute upper bound on the mixing angles of the dark matter sterile neutrino. Comparing this bound with existing astrophysical X-ray constraints, we find that the Dodelson-Widrow scenario, which proposes sterile neutrinos generated by active-sterile neutrino transitions to be the sole source of dark matter, is only possible for sterile neutrino masses lighter than 3.5 keV (6 keV if all hadronic uncertainties are pushed in one direction and the most stringent X-ray bounds are relaxed by a factor of two). This upper bound may conflict with a lower bound from structure formation, but a definitive conclusion necessitates numerical simulations with the non-equilibrium momentum distribution function that we derive. If other production mechanisms are also operative, no upper bound on the sterile neutrino mass can be established.

NEUTRINO SPIN OSCILLATIONS IN GRAVITATIONAL FIELDS

We study neutrino spin oscillations in gravitational fields. The quasi-classical approach is used to describe the neutrino spin evolution. First we examine the case of a weak gravitational field. We obtain the effective Hamiltonian for the description of neutrino spin oscillations. We also receive the neutrino transition probability when a particle propagates in the gravitational field of a rotating massive object. Then we apply the general technique to the description of neutrino spin oscillations in the Schwarzschild metric. The neutrino spin evolution equation for the case of the neutrino motion in the vicinity of a black hole is obtained. The effective Hamiltonian and the transition probability are also derived. We examine the neutrino oscillations process on different circular orbits and analyze the frequencies of spin transitions. The validity of the quasi-classical approach is also considered.