14369819
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.
15943616
High-energy neutrino conversion and the lepton asymmetry in the universe
We study the matter effects on oscillations of high-energy neutrinos in the Universe. A substantial effect can be produced by scattering of the neutrinos from cosmological sources $(z\ensuremath{\gtrsim}1)$ on the relic neutrino background, provided that the latter has large $\mathrm{CP}$ asymmetry: $\ensuremath{\eta}\ensuremath{\equiv}{(n}_{\ensuremath{\nu}}\ensuremath{-}{n}_{\overline{\ensuremath{\nu}}}{)/n}_{\ensuremath{\gamma}}\ensuremath{\gtrsim}1,$ where ${n}_{\ensuremath{\nu}},$ ${n}_{\overline{\ensuremath{\nu}}}$ and ${n}_{\ensuremath{\gamma}}$ are the concentrations of neutrinos, antineutrinos, and photons. We consider in detail the dynamics of conversion in the expanding neutrino background. Applications are given to the diffuse fluxes of neutrinos from gamma ray bursters, active galactic nuclei, and the decay of superheavy relics. We find that the vacuum oscillation probability can be modified by $\ensuremath{\sim}10\ensuremath{-}20%,$ and in extreme cases allowed by present bounds on $\ensuremath{\eta}$ the effect can reach $\ensuremath{\sim}100%.$ The signatures of matter effects would consist (i) for both active-active and active-sterile conversion, in a deviation of the numbers of events produced in a detector by neutrinos of different flavors, ${N}_{\ensuremath{\alpha}}$ $(\ensuremath{\alpha}=e,\ensuremath{\mu},\ensuremath{\tau}),$ and of their ratios from the values given by vacuum oscillations; such deviations can reach $\ensuremath{\sim}5\ensuremath{-}15%,$ and (ii) for active-sterile conversion, in a characteristic energy dependence of the ratios ${N}_{e}{/N}_{\ensuremath{\mu}}{,N}_{e}{/N}_{\ensuremath{\tau}}{,N}_{\ensuremath{\mu}}{/N}_{\ensuremath{\tau}}.$ Searches for these matter effects will probe large $\mathrm{CP}$ and lepton asymmetries in the Universe.
126012910
Physics of Supernova Neutrinos
89609700
Cosmic strings as emitters of extremely high energy neutrinos
We study massive particle radiation from cosmic string kinks, and its observability in extremely high energy neutrinos. In particular, we consider the emission of moduli --- weakly coupled scalar particles predicted in supersymmetric theories --- from the kinks of cosmic string loops. Since kinks move at the speed of light on strings, moduli are emitted with large Lorentz factors, and eventually decay into many pions and neutrinos via hadronic cascades. The produced neutrino flux has energy $E \gtrsim 10^{11} \rm{GeV}$, and is affected by oscillations and absorption (resonant and non-resonant). It is observable at upcoming neutrino telescopes such as JEM-EUSO, and the radio telescopes LOFAR and SKA, for a range of values of the string tension, and of the mass and coupling constant of the moduli.
19626167
Diffuse neutrino flux from failed supernovae.
I study the diffuse flux of electron antineutrinos from stellar collapses with direct black hole formation (failed supernovae). This flux is more energetic than that from successful supernovae, and therefore it might contribute substantially to the total diffuse flux above realistic detection thresholds. The total flux might be considerably higher than previously thought, and approach the sensitivity of Super-Kamiokande. For more conservative values of the parameters, the flux from failed supernovae dominates for antineutrino energies above 30-45 MeV, with potential to give an observable spectral distortion at megaton detectors.
118966003
Supernova neutrinos: Earth matter effects and neutrino mass spectrum
We perform a detailed study of the Earth matter effects on supernova neutrinos. The dependences of these effects on the properties of the original neutrino fluxes, on the trajectory of the neutrinos inside the Earth and on the oscillation parameters are described. We show that, for a large fraction (60 %) of the possible arrival times of the signal, the neutrino flux crosses a substantial amount of the matter of the Earth at least for one of the existing detectors. For oscillation parameters from the LMA solution of the solar neutrino problem the Earth matter effect consists in an oscillatory modulation of the $\barnue$ and/or $\nu_e$ energy spectra. The relative deviation with respect to the undistorted spectra can be as large as 20-30 % for E>20 MeV and 70-100 % for E>40 MeV. For parameters from the SMA and LOW solutions the effect is localized at low energies (E<10 MeV) and is not larger than 10 %. The Earth matter effects can be revealed (i) by the observation of oscillatory distortions of the energy spectra in a single experiment and (ii) by the comparison between the spectra at different detectors. For a supernova at distance D=10 Kpc, comparing the results of SuperKamiokande (SK), SNO and LVD experiments one can establish the effect at (2-3) \sigma level, whereas larger statistical significance ((4-5) \sigma) is obtained if two experiments of SK-size or larger are available. Studies of the Earth matter effect will select or confirm the solution of the solar neutrino problem, probe the mixing U_{e 3} and identify the hierarchy of the neutrino mass spectrum.
14369819
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.