236 research outputs found

    Distortion of the acoustic peaks in the CMBR due to a primordial magnetic field

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    In this paper we study the effect of a magnetic field on the fluctuation spectrum of the cosmic microwave background. We find that upcoming measurements might give interesting bounds on large scale magnetic fields in the early Universe. If the effects are seen, it might be possible to establish the presence of different fields in different patches of the sky. Absence of any effect, will provide by one order of magnitude a better limit for a primordial field, now given by nucleosynthesis.Comment: 10 pages, 2 .ps figures included, extra reference added and typographical errors correcte

    Active-active and active-sterile neutrino oscillation solutions to the atmospheric neutrino anomaly

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    We perform a fit to the full data set corresponding to 33.3 kt-yr of data of the Super-Kamiokande experiment as well as to all other experiments in order to compare the two most likely solutions to the atmospheric neutrino anomaly in terms of oscillations in the ΜΌ→Μτ\nu_\mu \to \nu_\tau and ΜΌ→Μs\nu_\mu \to \nu_s channels. Using state-of-the-art atmospheric neutrino fluxes we have determined the allowed regions of oscillation parameters for both channels. We find that the Δm2\Delta m^2 values for the active-sterile oscillations (both for positive and negative Δm2\Delta m^2) are higher than for the ΜΌ→Μτ\nu_\mu \to \nu_\tau case, and that the increased Super-Kamiokande sample slightly favours ΜΌ→Μτ\nu_\mu \to \nu_\tau oscillations over oscillations into a sterile species Îœs\nu_s, ΜΌ→Μs\nu_\mu \to \nu_s, and disfavours ΜΌ→Μe\nu_\mu \to \nu_e. We also give the zenith angle distributions predicted for the best fit points in each of the possible oscillation channels. Finally we compare our determinations of the atmospheric neutrino oscillation parameters with the expected sensitivities of future long-baseline experiments K2K, MINOS, ICARUS, OPERA and NOE.Comment: Updated to 535 days of Super-Kamiokande and corresponding modifications in the discussion and figures. Some References adde

    Limits on Active-Sterile Neutrino Mixing and the Primordial Deuterium Abundance

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    Studies of limits on active-sterile neutrino mixing derived from big bang nucleosynthesis considerations are extended to consider the dependance of these constraints on the primordial deuterium abundance. This study is motivated by recent measurements of D/H in quasar absorption systems, which at present yield discordant results. Limits on active-sterile mixing are somewhat relaxed for high D/H. For low D/H (≈2×10−5\approx 2 \times 10^{-5}), no active-sterile neutrino mixing is allowed by currently popular upper limits on the primordial 4^4He abundance YY. For such low primordial D/H values, the observational inference of active-sterile neutrino mixing by upcoming solar neutrino experiments would imply that YY has been systematically underestimated, unless there is new physics not included in standard BBN.Comment: 10 pages + 2 figures, uses revtex macros, submitted to Phys. Rev. D. Corrected figure captions and an added referenc

    Neutrino Decay as an Explanation of Atmospheric Neutrino Observations

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    We show that the observed zenith angle dependence of the atmospheric neutrinos can be accounted for by neutrino decay. Furthermore, it is possible to account for all neutrino anomalies with just three flavors.Comment: 4 pages, 1 figur

    Models of Light Singlet Fermion and Neutrino Phenomenology

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    We suggest that a singlet fermion SS exists beyond the standard see-saw structure. It mixes with light neutrinos via interactions with the right-handed neutrino components, so that \n_e \to S conversion solves the solar neutrino problem. Supersymmetry endowed with R-symmetry is shown to give a natural framework for existence, mass scale and mixing (sin⁥22th⁥es∌(0.1−1.5)⋅10−2\sin^22\th_{es} \sim (0.1-1.5)\cdot 10^{-2}) of such a fermion. Models with an approximate horizontal symmetry are constructed, which embed the fermion SS and explain simultaneously solar, atmospheric, hot dark matter problems as well as may predict the oscillation \bar{\n}_\m \to \bar{\n}_e in the region of sensitivity of KARMEN and LSND experiments.Comment: 14 pages, latex, no figure

    Light Gravitinos as Mixed Dark Matter

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    In theories with a gauge-mediated mechanism of supersymmetry breaking the gravitino is likely to be the lightest superparticle and, hence, a candidate for dark matter. We show that the decay of the next-to-lightest superparticle into a gravitino can yield a non-thermal population of gravitinos which behave as a hot dark matter component. Together with the warm component, which is provided by the population of gravitinos of thermal origin, they can give rise to viable schemes of mixed dark matter. This realization has some specific and testable features both in particle physics and astrophysics. We outline under which conditions the mechanism remains viable even when R parity is broken.Comment: 18 pages, LaTeX, no figur
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