Short-Baseline Electron Neutrino Disappearance, Tritium Beta Decay and Neutrinoless Double-Beta Decay

We consider the interpretation of the MiniBooNE low-energy anomaly and the Gallium radioactive source experiments anomaly in terms of short-baseline electron neutrino disappearance in the framework of 3+1 four-neutrino mixing schemes. The separate fits of MiniBooNE and Gallium data are highly compatible, with close best-fit values of the effective oscillation parameters Delta m^2 and sin^2 2 theta. The combined fit gives Delta m^2 >~ 0.1 eV^2 and 0.11 < sin^2 2 theta < 0.48 at 2 sigma. We consider also the data of the Bugey and Chooz reactor antineutrino oscillation experiments and the limits on the effective electron antineutrino mass in beta-decay obtained in the Mainz and Troitsk Tritium experiments. The fit of the data of these experiments limits the value of sin^2 2 theta below 0.10 at 2 sigma. Considering the tension between the neutrino MiniBooNE and Gallium data and the antineutrino reactor and Tritium data as a statistical fluctuation, we perform a combined fit which gives Delta m^2 \simeq 2 eV and 0.01 < sin^2 2 theta < 0.13 at 2 sigma. Assuming a hierarchy of masses m_1, m_2, m_3 << m_4, the predicted contributions of m_4 to the effective neutrino masses in beta-decay and neutrinoless double-beta-decay are, respectively, between about 0.06 and 0.49 and between about 0.003 and 0.07 eV at 2 sigma. We also consider the possibility of reconciling the tension between the neutrino MiniBooNE and Gallium data and the antineutrino reactor and Tritium data with different mixings in the neutrino and antineutrino sectors. We find a 2.6 sigma indication of a mixing angle asymmetry.Comment: 14 pages; final version published in Phys.Rev.D82:053005,201

Short-Baseline Active-Sterile Neutrino Oscillations?

We suggest the possibility that the anomalies observed in the LSND experiment and the Gallium radioactive source experiments may be due to neutrino oscillations generated by a large squared-mass difference of about 20 - 30 eV^2. We consider the simplest 3+1 four-neutrino scheme that can accommodate also the observed solar and atmospheric neutrino oscillations. We show that, in this framework, the disappearance of nu_e and nu_mu in short-baseline neutrino oscillation experiments is mainly due to active-sterile transitions. The implications of the first MiniBooNE results, appeared after the completion of this paper, are discussed in an addendum.Comment: 12 pages. The implications of the first MiniBooNE results are discussed in an addendu

nu_e Disappearance in MiniBooNE

The anomalous excess of low-energy nu_e events measured in the MiniBooNE experiment is explained through a renormalization of the absolute neutrino flux and a simultaneous disappearance of the nu_e's in the beam, which is compatible with that indicated by the results of Gallium radioactive source experiments. We present the results of the fit of MiniBooNE data (P(nu_e->nu_e) = 0.64 +0.08 -0.07) and the combined fit of MiniBooNE data and the nu_e disappearance measured in the Gallium radioactive source experiments, which gives P(nu_e->nu_e) = 0.82 +- 0.04. We show that our interpretation of the data is also compatible with an old indication in favor of nu_e disappearance found from the analysis of the results of beam-dump experiments, leading to P(nu_e->nu_e) = 0.80 +0.03 -0.04.Comment: 17 pages. Final version published in Phys. Rev. D 77, 093002 (2008

On neutrino-atom scattering in searches for neutrino magnetic moments

In the experimental searches for neutrino magnetic moments using germanium detectors one studies the ionization channel in the neutrino-atom scattering. We find that the so-called stepping approximation to the neutrino-impact ionization is exact in the semiclassical limit, and that the deviations from this approximation are very small.Comment: 1 page, to appear in Nuclear Physics B Proceedings Supplement 2011 (Proceedings of the XXIV International Conference on Neutrino Physics and Astrophysics, Athens, June 14-19, 2010

Electromagnetic properties of neutrinos

A short review on electromagnetic properties of neutrinos is presented. In spite of many efforts in the theoretical and experimental studies of neutrino electromagnetic properties, they still remain one of the main puzzles related to neutrinos.Comment: The talk presented by A.Studenikin at the International Conference on Topics in Astroparticle and Underground Physics, Rome (Italy), July 1-5, 200

Paradoxes of neutrino oscillations

Despite the theory of neutrino oscillations being rather old, some of its basic issues are still being debated in the literature. We discuss, in the framework of the wave packet approach, a number of such issues, including the relevance of the "same energy" and "same momentum" assumptions, the role of quantum-mechanical uncertainty relations in neutrino oscillations, the dependence of the production/detection and propagation coherence conditions that ensure the observability of neutrino oscillations on neutrino energy and momentum uncertainties, the question of (in)dependence of the oscillation probabilities on the neutrino production and detection processes, the applicability limits of the stationary source approximation, and Lorentz invariance of the oscillation probability. We also develop a novel approach to calculation of the oscillation probability in the wave packet picture, based on the summation/integration conventions different from the standard one, which gives a new insight into the oscillation phenomenology. We discuss a number of apparently paradoxical features of the theory of neutrino oscillations.Comment: LaTeX, 45 pages, no figures. v2: references adde

Electromagnetic neutrino-atom collisions: The role of electron binding

We present a new theoretical approach to neutrino-impact atomic excitation and/or ionization due to neutrino magnetic moments. The differential cross section of the process is given by a sum of the longitudinal and transverse terms, which are induced by the corresponding components of the force that the neutrino magnetic moment imposes on electrons with respect to momentum transfer. In this context, the recent theoretical studies devoted to the magnetic neutrino scattering on atoms are critically examined.Comment: 4 pages, published in proceedings of NOW201