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Posts: 131433
Date:
 Sterile neutrinos Permalink Narrowing the window on sterile neutrinosA major international collaboration between the MINOS experiment, which involves UCL scientists, and the Daya Bay experiment has today announced results which shed new light on one of the most pressing questions in particle physics - do sterile neutrinos exist? Read more __________________

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Posts: 131433
Date:
 RE: Sterile Neutrino Production Permalink Title: Are Light Sterile Neutrinos Consistent with Supernova Explosions? Authors: Meng-Ru Wu, Tobias Fischer, Gabriel Martínez-Pinedo, Yong-Zhong Qian We point out that for sterile neutrinos of the eV mass scale with mixing parameters suggested by the reactor neutrino anomaly, substantial flavour transformation occurs in both \nu_e-\nu_s and \bar \nu_e-\bar \nu_s channels near a supernova core where the electron-to-baryon ratio is \approx 1/3. We show that the rate of heating by neutrino reactions in the shocked material is significantly reduced for ~ 100 ms after the launch of the shock in spherically symmetric models of 8.8 and 11.2 solar masses supernovae. While the exact consequences must be evaluated by incorporating \nu_e-\nu_s and \bar \nu_e-\bar \nu_s conversion self-consistently in the models, our results suggest that such flavour transformation would have important effects on the supernova explosion mechanisms and possibly also on nucleosynthesis in the neutrino-heated ejecta. We explore the sensitivity of our results to the mixing parameters and urge that self-consistent supernova models be developed to constrain the allowed parameter space. Read more (42kb, PDF) __________________

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Posts: 131433
Date:
 Permalink Title: Electron-positron Annihilation Lines and Decaying Sterile Neutrinos Authors: M. H. Chan, M.-C. Chu If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences. We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way center, and we thus obtain bounds on the sterile neutrino decay rate \Gamma_e \ge 10^{-28} s^{-1} from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of 1.2 x 10^{-4}-9.7 x 10^{-4} ph cm^{-2} s^{-1} from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate the flux of active neutrinos produced by sterile neutrino decays to be 0.02-0.1 cm^{-2} s^{-1} passing through the earth. Read more (37kb, PDF) __________________

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Posts: 131433
Date:
 Permalink Title: Testing for Large Extra Dimensions with Neutrino OscillationsAuthors: P. A. N. Machado, H. Nunokawa, R. Zukanovich FunchalWe consider a model where sterile neutrinos can propagate in a large compactified extra dimension giving rise to Kaluza-Klein (KK) modes and the Standard Model left-handed neutrinos are confined to a 4-dimensional spacetime brane. The KK modes mix with the standard neutrinos modifying their oscillation pattern. We examine current experiments such as KamLAND and MINOS to estimate the impact of the possible presence of such KK modes on the determination of the neutrino oscillation parameters and simultaneously obtain limits on the size of the largest extra dimension. We found that the presence of the KK modes do not essentially improve the quality of the fit compared to the case of the standard oscillation. By combining the results from KamLAND and MINOS, in the limit of a vanishing lightest neutrino mass, we obtain the stronger bound on the size of the extra dimension as ~ 0.9 \mu m at 99% CL. If the lightest neutrino mass turn out to be larger, 0.2 eV, for example, we obtain the bound ~ 0.2 \mu m. We also discuss the expected sensitivities on the size of the extra dimension for future experiments such as Double CHOOZ, T2K and NOvA. Read more (827kb, PDF) __________________

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Posts: 131433
Date:
 Permalink Physics experiment suggests existence of new particleThe results of a high-profile Fermilab physics experiment involving a University of Michigan professor appear to confirm strange 20-year-old findings that poke holes in the standard model, suggesting the existence of a new elementary particle: a fourth flavour of neutrino.The new results go further to describe a violation of a fundamental symmetry of the universe asserting that particles of antimatter behave in the same way as their matter counterparts.Neutrinos are neutral elementary particles born in the radioactive decay of other particles. The known "flavours" of neutrinos are the neutral counterparts of electrons and their heavier cousins, muons and taus. Regardless of a neutrino's original flavour, the particles constantly flip from one type to another in a phenomenon called "neutrino flavour oscillation."Read more __________________

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Posts: 131433
Date:
 Sterile Neutrinos Permalink A ghostly particle given up for dead is showing signs of life.Not only could this "sterile" neutrino be the stuff of dark matter, thought to make up the bulk of our universe, it might also help to explain how an excess of matter over antimatter arose in our universe.Neutrinos are subatomic particles that rarely interact with ordinary matter. They are known to come in three flavours - electron, muon and tau - with each able to spontaneously transform into another.In the 1990s, results from the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos National Laboratory in New Mexico suggested there might be a fourth flavour: a "sterile" neutrino that is even less inclined to interact with ordinary matter than the others.Read more __________________

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Posts: 131433
Date:
 Sterile Neutrino Production Permalink Title: Lepton Number-Driven Sterile Neutrino Production in the Early UniverseAuthors: Chad T. Kishimoto, George M. FullerWe examine medium-enhanced, neutrino scattering-induced decoherent production of dark matter candidate sterile neutrinos in the early universe. In cases with a significant net lepton number we find two resonances, where the effective in-medium mixing angles are large. We calculate the lepton number depletion-driven evolution of these resonances. We describe the dependence of this evolution on lepton numbers, sterile neutrino rest mass, and the active-sterile vacuum mixing angle. We find that this resonance evolution can result in relic sterile neutrino energy spectra with a generic form which is sharply peaked in energy. We compare our complete quantum kinetic equation treatment with the widely-used quantum Zeno ansatz. Read more (89kb, PDF) __________________
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