Neutrino Conversion Research Articles

Unstable relics as a source of galactic positrons

We calculate the fluxes of 511 keV photons from the galactic bulge caused by positrons produced in the decays of relic particles with masses less than 100 MeV. In particular, we tighten the constraints on sterile neutrinos over a large domain of the mass-mixing angle parameter space, where the resulting photon flux would significantly exceed the experimental data. At the same time, the observed photon fluxes can be easily caused by decaying sterile neutrinos in the mass range 1<msterile≲50 MeV with the cosmological abundance typically within 10−9≲Ωsterile≲10−5, assuming that Ωsterile comes entirely from the conversion of active neutrinos in the early universe. Other candidates for decaying relics such as neutral (pseudo)scalar particles coupled to leptons with the gravitational strength can be compatible with the photon flux, and can constitute the main component of cold dark matter.

Toward precision measurements in solar neutrinos

Solar neutrino physics enters a stage of precision measurements. In this connection we present a precise analytic description of the neutrino conversion in the context of LMA-MSW solution of the solar neutrino problem. Using the adiabatic perturbation theory we derive an analytic formula for the ν e survival probability which takes into account the non-adiabatic corrections and the regeneration effect inside the Earth. The probability is averaged over the neutrino production region. We find that the non-adiabatic corrections are of the order 10 −9–10 −7. Using the formula for the Earth regeneration effect we discuss features of the zenith angle dependence of the ν e flux. In particular, we show that effects of small structures at the surface of the Earth can be important.

Neutrino signatures of supernova forward and reverse shock propagation

A few seconds after bounce in a core-collapse supernova, the shock wave passes the densityregion corresponding to resonant neutrino oscillations with the ‘atmospheric’ neutrino massdifference. The transient violation of the adiabaticity condition manifests itself in anobservable modulation of the neutrino signal from a future galactic supernova. In additionto the shock wave propagation effects that were previously studied, a reverse shock formswhen the supersonically expanding neutrino-driven wind collides with the slower earliersupernova ejecta. This implies that for some period the neutrinos pass two subsequentdensity discontinuities, giving rise to a ‘double-dip’ feature in the average neutrino energyas a function of time. We study this effect both analytically and numerically and findthat it allows one to trace the positions of the forward and reverse shocks. Weshow that the energy dependent neutrino conversion probabilities allow one todetect oscillations even if the energy spectra of different neutrino flavours are thesame as long as the fluxes differ. These features are observable in the signal for an inverted and in theνe signal for a normal neutrino mass hierarchy, provided the 13-mixing angle is ‘large’ ().

Constraining the neutrino magnetic moment with antineutrinos from the sun.

We discuss the impact of different solar neutrino data on the spin-flavor-precession (SFP) mechanism of neutrino conversion. We find that, although detailed solar rates and spectra allow the SFP solution as a subleading effect, the recent KamLAND constraint on the solar antineutrino flux places stronger constraints on this mechanism. Moreover, we show that for the case of random magnetic fields inside the Sun, one obtains a more stringent constraint on the neutrino magnetic moment down to the level of mu(nu)< or = few x 10(-12)mu(B), similar to bounds obtained from star cooling.

Solar neutrinos: the SNO salt phase results and physics of conversion

We have performed analysis of the solar neutrino data including results from the SNO salt phase as well as the combined analysis of the solar and the KamLAND results. The best-fit values of neutrino parameters are Δ m 2=7.1×10 −5 eV 2, tan 2 θ=0.40 with the boron flux f B=1.04. New SNO results strongly disfavor maximal mixing and the h-LMA region (Δ m 2>10 −4 eV 2) which is accepted now at the 3 σ level. We find the 3 σ upper bounds: Δ m 2<1.7×10 −4 eV 2 and tan 2 θ<0.64, and the lower bound Δ m 2>4.8×10 −5 eV 2. Non-zero 13-mixing does not change these results significantly. The present data determine quantitatively the physical picture of the solar neutrino conversion. At high energies relevant for SNO and Super-Kamiokande the deviation of the effective survival probability from the non-oscillatory value is about 10–14%. The oscillation effect contribution to this difference is about 10% and the earth regeneration about 3–4%. At low energies ( E<1 MeV) the matter corrections to vacuum oscillation effect are below 5%. The predictions for the forthcoming measurements are given which include the spectral distortion and CC/NC ratio at SNO, the day–night asymmetry, the KamLAND spectrum and rate.

Collider tests for neutrino mass generation in a supersymmetric world with R-parity violation

We summarize the low energy features of a supersymmetric class of models with bilinear R-parity violation. We analyze two cases where the supersymmetry breaking is mediated either by supergravity or by anomaly induced contributions to the soft parameters and compare both scenarios in the context of recent neutrino conversion data and collider physics. We show that both classes of models have a large potential to discoveries in collider experiments as well as in neutrino experiments.

Gravitational waves from a pulsar kick caused by neutrino conversions

It has been suggested that the observed pulsar velocities are caused by an asymmetric neutrino emission from a hot neutron star during the first seconds after the supernova collapse. We calculate the magnitude of gravitational waves produced by the asymmetries in the emission of neutrinos. The resulting periodic gravitational waves may be detectable by LIGO and LISA in the event of a nearby supernova explosion.

Supernova prompt neutronization neutrinos and neutrino magnetic moments

It is shown that the combined action of spin–flavour conversions of supernova neutrinos due to the interactions of their Majorana-type transition magnetic moments with the supernova magnetic fields and flavour conversions due to the mass mixing can lead to the transformation of νe born in the neutronization process into their antiparticles ν̄e. Such an effect would have a clear experimental signature and its observation would be a `smoking gun' evidence for the neutrino transition magnetic moments. It would also signify a value of the leptonic mixing parameter |Ue3| in excess of 10−2.

Classical mode conversion description of neutrino oscillations in dense magnetized plasmas

Neutrino oscillations in dense magnetized plasmas, similar to those found in supernovas, are described. The adopted model is similar to the classical mode conversion problems examined in fluid dynamics and plasma physics. This approach allows for the derivation of analytical results for the neutrino conversion probability for different combinations of background density profile and magnetic field profile.

Supernova neutrino spectrum with matter and spin flavour precessioneffects

We consider Majorana neutrino conversions inside supernovae by taking intoaccount both flavour mixing and the neutrino magnetic moment. We study theadiabaticity of various possible transitions between the neutrino states forboth normal and inverted hierarchy within the various solar neutrino problemsolutions. From the final mass spectrum within diffrent scenarios, we inferthe consequences of the various conversion effects on the neutronizationpeak, the nature of final spectra, and the possible Earth matter effect onthe final fluxes. This enables us to check the sensitivity of the SNneutrino flux on magnetic moment interaction, and narrow down possiblescenarios which depend on the normal or inverted mass spectrum, thesolution of the solar neutrino problem and the value of μB.

Do many-particle neutrino interactions cause a novel coherent effect?

We investigate whether coherent flavor conversion of neutrinos in a neutrino background is substantially modified by many-body effects, with respect to the conventional one-particle effective description. We study the evolution of a system of interacting neutrino plane waves in a box. Using its equivalence to a system of spins, we determine the character of its behavior completely analytically. We find that, if the neutrinos are initially in flavor eigenstates, no coherent flavor conversion is realized, in agreement with the effective one-particle description. This result does not depend on the size of the neutrino wavepackets and therefore has a general character. The validity of the several important applications of the one-particle formalism is thus confirmed.

Resonant spin-flavor conversion of supernova neutrinos: Dependence on presupernova models and future prospects

We study the resonant spin-flavor (RSF) conversion of supernova neutrinos, which is induced by the interaction between the nonzero neutrino magnetic moment and the supernova magnetic fields, and its dependence on presupernova models. As the presupernova models, we adopt the latest ones by Woosley, Heger, and Weaver, and, further, models with both solar and zero metallicity are investigated. Since the $(1-2Y_e)$ profile of the new presupernova models, which is responsible for the RSF conversion, suddenly drops at the resonance region, the completely adiabatic RSF conversion is not realized, even if $\mu_\nu B_0= (10^{-12}\mu_B)(10^{10} G)$, where $B_0$ is the strength of the magnetic field at the surface of the iron core. In particular for the model with zero metallicity, the conversion is highly nonadiabatic in the high energy region, reflecting the $(1-2Y_e)$ profile of the model. In calculating the flavor conversion, we find that the shock wave propagation, which changes density profiles drastically, is a much more severe problem than it is for the pure Mikheyev-Smirnov-Wolfenstein (MSW) conversion case. This is because the RSF effect occurs at a far deeper region than the MSW effect. To avoid the uncertainty concerning the shock propagation, we restrict our discussion to 0.5 s after the core bounce (and for more conservative discussion, 0.25 s), during which the shock wave is not expected to affect the RSF region. We also evaluate the energy spectrum at the Super-Kamiokande detector for various models using the calculated conversion probabilities, and find that it is very difficult to obtain useful information on the supernova metallicities and magnetic fields or on the neutrino magnetic moment from the supernova neutrino observation. Future prospects are also discussed.

High-energy neutrino conversion into an electron-Wpair in a magnetic field and its contribution to neutrino absorption

We calculate the conversion rate of high-energy neutrinos propagating in a constant magnetic field into an electron-$W$ pair $(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\nu}}W+e)$ from the imaginary part of the neutrino self-energy. Using the exact propagators in a constant magnetic field, the neutrino self-energy has been calculated to all orders in the field within the Weinberg-Salam model. We obtain a compact formula in the limit of $B\ensuremath{\ll}{B}_{\mathrm{cr}}\ensuremath{\equiv}{m}^{2}/e.$ We find that above the process threshold ${E}^{(\mathrm{th})}\ensuremath{\approx}2.2\ifmmode\times\else\texttimes\fi{}{10}^{16}\mathrm{eV}\ifmmode\times\else\texttimes\fi{}{(B}_{\mathrm{cr}}/B)$ this contribution to the absorption of neutrinos yields an asymptotic absorption length $\ensuremath{\approx}1.1\mathrm{m}\mathrm{}\ifmmode\times\else\texttimes\fi{}{(B}_{\mathrm{cr}}{/B)}^{2}\ifmmode\times\else\texttimes\fi{}{(10}^{16}\mathrm{eV}/E).$

Three-generation study of neutrino spin-flavor conversion in supernovae and implication for the neutrino magnetic moment

We investigate resonant spin-flavor (RSF) conversions of supernova neutrinos which are induced by the interaction of neutrino magnetic moment and supernova magnetic fields. From the formulation which includes all three-flavor neutrinos and anti-neutrinos, we give a new crossing diagram that includes not only ordinary MSW resonance but also magnetically-induced RSF effect. With the diagram, it is found that four conversions occur in supernova, two are induced by the RSF effect and two by the pure MSW. We also numerically calculate neutrino conversions in supernova matter, using neutrino mixing parameters inferred from recent experimental results and a realistic supernova progenitor model. The results indicate that until 0.5 seconds after core bounce, the RSF-induced $\bar{\nu}_e \leftrightarrow \nu_\tau$ transition occurs efficiently (adiabatic resonance), when $\mu_\nu \agt 10^{-12} \mu_B (B_0 / 5 \times 10^{9} \mathrm G)^{-1}$, where $B_0$ is the strength of the magnetic field at the surface of iron core. We also evaluate the energy spectrum as a function of $\mu_\nu B_0$ at the SuperKamiokande detector and the Sudbury Neutrino Observatory using the calculated conversion probabilities, and find that the spectral deformation might have possibility to provide useful information on neutrino magnetic moment as well as magnetic field strength in supernovae.

Solar neutrino oscillations and bounds on neutrino magnetic moment and solar magnetic field

If the observed deficit of solar neutrinos is due to neutrino oscillations, neutrino conversions caused by the interaction of their transition magnetic moments with the solar magnetic field (spin-flavour precession) can still be present at a subdominant level. In that case, the combined action of neutrino oscillations and spin-flavour precession can lead to a small but observable flux of electron antineutrinos coming from the sun. Non-observation of these ν̄e's could set limits on neutrino transition moment μ and the strength and coordinate dependence of the solar magnetic field B⊥. The sensitivity of the ν̄e flux to the product μB⊥ is the strongest in the case of the vacuum oscillation (VO) solution of the solar neutrino problem; in the case of the LOW solution, it is weaker, and it is the weakest for the LMA solution. For different solutions, different characteristics of the solar magnetic field B⊥(r) are probed: for the VO solution, the ν̄e flux is determined by the integral of B⊥(r) over the solar convective zone, for LMA it is determined by the magnitude of B⊥ in the neutrino production region, and for LOW it depends on the competition between this magnitude and the derivative of B⊥(r) at the surface of the sun.

Supernova neutrinos: difference of νμ– ντ fluxes and conversion effects

The formalism of flavor conversion of supernova neutrinos is generalized to include possible differences in the fluxes of the muon and tau neutrinos produced in the star. In this case the radiatively induced difference of the ν μ and ν τ potentials in matter becomes important. The ν μ and ν τ flux differences can manifest themselves in the effects of the Earth matter on the observed ν e ( ν ̄ e ) signal if: (i) the neutrino mass hierarchy is normal (inverted); (ii) the solution of the solar neutrino problem is in the LMA region; (iii) the mixing U e3 is relatively large: | U e3 | 2≳10 −3. We find that for differences in the ν μ – ν τ ( ν ̄ μ – ν ̄ τ ) average energies and/or integrated luminosities ≲20%, the relative deviation of the observed ν e ( ν ̄ e ) energy spectrum at E≳50 MeV from that in the case of the equal fluxes can reach ∼20–30% (∼10–15%) for neutrinos crossing the Earth. It could be detected in future if large detectors sensitive to the ν e ( ν ̄ e ) energy spectrum become available. The study of this effect would allow one to test the predictions of the ν μ , ν τ , ν ̄ μ , ν ̄ τ fluxes from supernova models and therefore give an important insight into the properties of matter at extreme conditions. It should be taken into account in the reconstruction of the neutrino mass spectrum and mixing matrix from the supernova neutrino observations. We show that even for unequal ν μ and ν τ fluxes, effects of leptonic CP violation cannot be studied in the supernova neutrino experiments.

Probing non-standard couplings of neutrinos at the Borexino detector

The present experimental status does not exclude weak-strength non-standard interactions of neutrinos with electrons. These interactions can be revealed in solar neutrino experiments. Our discussion covers several aspects related to this issue. First, we perform an analysis of the Super-Kamiokande and SNO data to investigate their sensitivity to such interactions. In particular, we show that the ν e oscillation into sterile neutrinos can be still allowed if ν e has extra interactions of the proper strength. Second, we suggest that the Borexino detector can provide good signatures for these non-standard interactions. Indeed, in Borexino the shape of the recoil electron spectrum from the νe→ νe scattering essentially does not depend on the solar neutrino conversion details, since most of the signal comes from the mono-energetic 7Be neutrinos. Hence, the partial conversion of solar ν e into a nearly equal mixture of ν μ and ν τ , as is indicated by the atmospheric neutrino data, offers the chance to test extra interactions of ν τ , or of ν e itself.

Active–sterile neutrino conversion: consequences for the r-process and supernova neutrino detection

We examine active–sterile neutrino conversion in the late time post-core-bounce supernova environment. By including the effect of feedback on the Mikheyev–Smirnov–Wolfenstein (MSW) conversion potential, we obtain a large range of neutrino mixing parameters which produce a favorable environment for the r-process. We look at the signature of this effect in the current generation of neutrino detectors now coming on line. We also investigate the impact of the neutrino–neutrino forward-scattering-induced potential on the MSW conversion.

Phenomenological analysis of properties of the right-handed Majorana neutrino in the seesaw mechanism

As an extension of our previous work in the seesaw mechanism, we analyze the influence of $U_{e3}$ on the properties (masses and mixing) of the RH Majorana neutrinos in three flavors. The quasidegenerate light neutrinos case is also considered. Assuming the hierarchical Dirac neutrino masses, we find the heavy Majorana neutrino mass spectrum is either hierarchical or partial degenerate if $\theta_{23}^{\nu}$ is large. We show that degenerate RH Majorana masses correspond to maximal RH mixing angle while hierarchical ones correspond to the RH mixing angles which scale linearly with the mass ratios of the Dirac neutrino masses. An interesting analogue with the behavior of the matter-enhanced neutrino conversion is also presented.

Rates of neutrino conversion and decay in hot and dense QED plasma

Using a real-time formalism of equilibrium and nonequilibrium quantum-field theory, we derive the reaction-rate formula for neutrino-conversion ($\nu \to \nu'$) process and $\nu \bar{\nu}'$ annihilation process, which take place in a hot and dense QED plasma with background (anti)neutrinos out of equilibrium. Also derived is the formula for the inverse processes to the above ones. Using the hard-thermal-loop resummation scheme, we include the contribution from the coherent processes. The decay/production of a neutrino causes an evolution of its spatial distribution. A scheme for dealing with this evolution is presented. For the case of isotropic neutrino distribution, numerical computation is carried out for the parameter region of type-II super-nova explosion. Defferential reaction rate exhibits characteristic peak structure, which comes from the coherent processes. The contribution from the above processes to the decay or damping rate of a parent neutrino $\nu$ is also studied.