289 research outputs found

    LSND versus MiniBooNE: Sterile neutrinos with energy dependent masses and mixing?

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    Standard active--sterile neutrino oscillations do not provide a satisfactory description of the LSND evidence for neutrino oscillations together with the constraints from MiniBooNE and other null-result short-baseline oscillation experiments. However, if the mass or the mixing of the sterile neutrino depends in an exotic way on its energy all data become consistent. I explore the phenomenological consequences of the assumption that either the mass or the mixing scales with the neutrino energy as 1/Eνr(r>0)1/E_\nu^r (r > 0). Since the neutrino energy in LSND is about 40 MeV, whereas MiniBooNE operates at around 1 GeV, oscillations get suppressed in MiniBooNE and the two results become fully compatible for r0.2r\gtrsim 0.2. Furthermore, also the global fit of all relevant data improves significantly by exploring the different energy regimes of the various experiments. The best fit χ2\chi^2 decreases by 12.7 (14.1) units with respect to standard sterile neutrino oscillations if the mass (mixing) scales with energy.Comment: 18 pages, 3 figures, discussion extended, version to appear in JHE

    Is the effect of the Sun's gravitational potential on dark matter particles observable?

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    We consider the effect of the Sun's gravitational potential on the local phase space distribution of dark matter particles, focusing on its implication for the annual modulation signal in direct detection experiments. We perform a fit to the modulation signal observed in DAMA/LIBRA and show that the allowed region shrinks if Solar gravitational focusing (GF) is included compared to the one without GF. Furthermore, we consider a possible signal in a generic future direct detection experiment, irrespective of the DAMA/LIBRA signal. Even for scattering cross sections close to the current bound and a large exposure of a xenon target with 270 ton yr it will be hard to establish the presence of GF from data. In the region of dark matter masses below 40 GeV an annual modulation signal can be established for our assumed experimental setup, however GF is negligible for low masses. In the high mass region, where GF is more important, the significance of annual modulation itself is very low. We obtain similar results for lighter targets such as Ge and Ar. We comment also on inelastic scattering, noting that GF becomes somewhat more important for exothermic scattering compared to the elastic case.Comment: 19 pages, 20 figures, 1 table, v2: added Fig. 3 for DAMA, and comments on light target

    Sterile neutrino oscillations after first MiniBooNE results

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    In view of the recent results from the MiniBooNE experiment we revisit the global neutrino oscillation fit to short-baseline neutrino data by adding one or two sterile neutrinos with eV-scale masses to the three Standard Model neutrinos, and for the first time we consider also the global fit with three sterile neutrinos. Four-neutrino oscillations of the (3+1) type have been only marginally allowed before the recent MiniBooNE results, and become even more disfavored with the new data (at the level of 4σ4\sigma). In the framework of so-called (3+2) five-neutrino mass schemes we find severe tension between appearance and disappearance experiments at the level of more than 3σ3\sigma, and hence no satistfactory fit to the global data is possible in (3+2) schemes. This tension remains also when a third sterile neutrino is added, and the quality of the global fit does not improve significantly in a (3+3) scheme. It should be noted, however, that in models with more than one sterile neutrino the MiniBooNE results are in perfect agreement with the LSND appearance evidence, thanks to the possibility of CP violation available in such oscillation schemes. Furthermore, if disappearance data are not taken into account (3+2) oscillations provide an excellent fit to the full MiniBooNE spectrum including the event excess at low energies.Comment: 30 pages, 12 figures, minor improvements of text and abstract, summary table added, matches version to be published in Phys. Rev.

    On the determination of the leptonic CP phase

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    The combination of data from long-baseline and reactor oscillation experiments leads to a preference of the leptonic CP phase δCP\delta_{\rm CP} in the range between π\pi and 2π2\pi. We study the statistical significance of this hint by performing a Monte Carlo simulation of the relevant data. We find that the distribution of the standard test statistic used to derive confidence intervals for δCP\delta_{\rm CP} is highly non-Gaussian and depends on the unknown true values of θ23\theta_{23} and the neutrino mass ordering. Values of δCP\delta_{\rm CP} around π/2\pi/2 are disfavored at between 2σ2\sigma and 3σ3\sigma, depending on the unknown true values of θ23\theta_{23} and the mass ordering. Typically the standard χ2\chi^2 approximation leads to over-coverage of the confidence intervals for δCP\delta_{\rm CP}. For the 2-dimensional confidence region in the (δCP,θ23\delta_{\rm CP},\theta_{23}) plane the usual χ2\chi^2 approximation is better justified. The 2-dimensional region does not include the value δCP=π/2\delta_{\rm CP} = \pi/2 up to the 86.3\% (89.2\%)~CL assuming a true normal (inverted) mass ordering. Furthermore, we study the sensitivity to δCP\delta_{\rm CP} and θ23\theta_{23} of an increased exposure of the T2K experiment, roughly a factor 12 larger than the current exposure and including also anti-neutrino data. Also in this case deviations from Gaussianity may be significant, especially if the mass ordering is unknown.Comment: 25 pages, 12 figures. Matches version which is to appear in JHEP. New appendix with the first anti-neutrino results from T2K is adde

    Determination of the neutrino mass ordering by combining PINGU and Daya Bay II

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    The relatively large measured value of theta_13 has opened various possiblities to determine the neutrino mass ordering, among them using PINGU, the low-energy extention of the IceCube neutrino telescope, to observe matter effects in atmospheric neutrinos, or a high statistics measurment of the neutrino energy spectrum at a reactor neutrino experiment with a baseline of around 60 km, such as the Daya Bay II project. In this work we point out a synergy between these two approaches based on the fact that when data are analysed with the wrong neutrino mass ordering the best fit occurs at different values of |Delta m^2_31| for PINGU and Daya Bay II. Hence, the wrong mass ordering can be excluded by a mismatch of the values inferred for |Delta m^2_31|, thanks to the excellent accuracy for Delta m^2_31 of both experiments. We perform numerical studies of PINGU and Daya Bay II sensitivities and show that the synergy effect may lead to a high significance determination of the mass ordering even in situations where the individual experiments obtain only poor sensitivity.Comment: 23 pages, 7 figures (15 eps files), typos and minor mistakes corrected, final version to appear in JHE

    The LSND puzzle in the light of MiniBooNE results

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    I give a brief overview over various attempts to reconcile the LSND evidence for oscillations with all other global neutrino data, including the results from MiniBooNE. I discuss the status of oscillation schemes with one or more sterile neutrinos and comment on various exotic proposals