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[en] Considering four-neutrino schemes of type 3+1, we identify four small regions of the neutrino mixing parameter space compatible with all data. Assuming a small mixing between the sterile neutrino and the isolated mass eigenstate we show that large νμ→ντ and νe→ντ transitions are predicted in short-baseline experiments and could be observed in the near future in dedicated experiments. We discuss also implications for solar, atmospheric and long-baseline neutrino experiments and we present a formalism that allows to describe in 3+1 schemes atmospheric neutrino oscillations, long-baseline νμ disappearance and νμ→ντ transitions in matter. (author)
[en] The NOMAD experiment has been designed to search for ντ appearance in the CERN wide-band neutrino beam. The detector is now completed and has been further improved. All subdetectors are working well. The experiment, where the search for oscillation is based on kinematical criteria, will reach the sensitivity Δm2> 0.7 eV2 for maximal mixing and Δm2> 50 eV2 for mixing angles sin2 2θ> 3.8.10-4 after 2 years of running, making possible to explore a region of cosmological interest. Preliminary measurements are presented from the 1994 and 1995 data samples. (orig.)
[en] The sensitivity of high-energy neutrino telescope in detecting μ's produced in the interactions in the earth of νμ, νμ of astrophysical origin, was calculated, via a Monte Carlo program, where the most recent parametrization of the nucleon parton distribution functions have been taken into account in the simulation of the νμ CC, νμ CC events. The dependence of the sensitivity on the parameters of the detector (energy threshold Eth and angular resolution σR) as well as on the source spectral index γ was determined. It was shown that, for energy threshold in the range 6 GeV ≤ Eth ≤ 100 GeV and angular resolution σR = 0.5-1.0·, the sensitivity does not critically depend on the spectral index γ. The hope is to use the results in designing new installation
[en] The problem of understanding why neutrino mixing is different from quark mixing is of fundamental importance today. The Majorana nature of neutrinos, totally different from the Dirac nature of quarks, could easily be the source of such a difference. In the most general case of a Dirac-Majorana mass term, the Majorana nature of neutrinos implies a mixing between active and sterile states, if they exist. Here we concentrate on electron neutrinos and assume that electron neutrinos can oscillate both into active states and into sterile states, with mixing angle similar to the Cabibbo angle. This assumption, together with a squared-mass difference at the eV2 scale, in order to account for the LSND anomaly, predicts a disappearance signal that is compatible with SNO-NC measurements in solar neutrinos and with Gallium calibration source recent results. Active-sterile oscillations of this kind could also affect electron neutrinos in MiniBoone. Comparison of this hypothesis with reactor limits suggests new measurements with future beta beams
[en] From the controversial data release of the OPERA-CNGS experiment (The OPERA collaboration 2011 arXiv:1109.4897), publicly announced on 23 September 2011 where muonic neutrinos seem to propagate at a speed faster than light, we cast a phenomenological model describing the behaviour of such a tachyonic neutrino, carrying an imaginary mass based on the Majorana tower of particles described in 1932. If the interpretation of OPERA data is correct and considering the strong constraints from the observations of the supernova SN1987a, we show that the tachyonic behaviour of the neutrino can occur only when it is propagating inside matter. Following this idea, within the experimental errors, we fit the data released by OPERA with those of MINOS and by assuming a superluminal propagation inside the matter of SN1987a, confirm our ansatz with stellar structure models of the supernova precursor. Monte Carlo simulations based on this fit agree well with the new OPERA data. Possible violations of Lorentz invariance due to quantum gravity effects have been considered. (paper)
[en] Recently, Warm (keV scale) Dark Matter emerged impressively over CDM (Cold Dark Matter) as the leading Dark Matter candidate. In the context of this new Dark Matter situation, which implies novelties in the astrophysical, cosmological and keV particle physics context, this 16. Paris Colloquium 2012 is devoted to the LambdaWDM Standard Model of the Universe. The topics of the colloquium are as follows: -) observational and theoretical progress on the nature of dark matter: keV scale warm dark matter, -) large and small scale structure formation in agreement with observations at large scales and small galactic scales, and -) neutrinos in astrophysics and cosmology. This document gathers the slides of the presentations.
[en] We perform a cosmological analysis in which we allow the primordial power spectrum of scalar perturbations to assume a shape that is different from the usual power-law predicted by the simplest models of cosmological inflation. We parameterize the free primordial power spectrum with a ''piecewise cubic Hermite interpolating polynomial'' (PCHIP). We consider a 3+1 neutrino mixing model with a sterile neutrino having a mass at the eV scale, which can explain the anomalies observed in short-baseline neutrino oscillation experiments. We find that the freedom of the primordial power spectrum allows to reconcile the cosmological data with a fully thermalized sterile neutrino in the early Universe. Moreover, the cosmological analysis gives us some information on the shape of the primordial power spectrum, which presents a feature around the wavenumber k=0.002 Mpc"−"1
[en] The search for neutron-antineutron (nanti n) oscillations conducted by a Heidelberg-ILL-Padova-Pavia collaboration at the European slow neutron facility at Grenoble requires a very strong cold neutron beam, but an extremely low neutron-induced radiation background. This article describes the analysis and suppression of neutron-beam-related background in the nanti n experiment. In particular, the fabrication of a 20 m2 shield of isotopically pure sintered 6LiF ceramics which protects the annihilation detector from the inside against neutrons scattered from the annihilation target is described. (orig.)
[en] The observed deficit in the Gallium radioactive source experiments may be interpreted as a possible indication of active-sterile νe mixing. In the effective framework of two-neutrino mixing we obtain sin22θ≥0.03 and Δm2≥0.1 eV2. The compatibility of this result with the data of the Bugey reactor ν-bare disappearance experiments is studied. It is found that the Bugey data present a hint of neutrino oscillations with 0.02≤sin22θ≤0.08 and Δm2∼1.8 eV2, which is compatible with the Gallium allowed region of the mixing parameters. This hint persists in the combined analysis of Gallium, Bugey, and Chooz data.
[en] The theory and phenomenology of light sterile neutrinos at the eV mass scale is reviewed. The reactor, gallium and Liquid Scintillator Neutrino Detector anomalies are briefly described and interpreted as indications of the existence of short-baseline oscillations which require the existence of light sterile neutrinos. The global fits of short-baseline oscillation data in 3 + 1 and 3 + 2 schemes are discussed, together with the implications for β-decay and neutrinoless double-β decay. The cosmological effects of light sterile neutrinos are briefly reviewed and the implications of existing cosmological data are discussed. The review concludes with a summary of future perspectives. (topical review)