Status of 3-neutrino and 4-neutrino scenarios

Some aspects of the current neutrino oscillation phenomenology are briefly discussed, with emphasis on the status of mass-mixing parameters relevant for scenarios with three active neutrinos, and with an additional fourth sterile neutrino.Comment: 3 pages (including 1 figure). Talk presented at NOW 2000, 2nd International Europhysics Neutrino Oscillation Workshop (Conca Specchiulla, Otranto, Italy), September 9-16, 2000, to be published in Nucl. Phys. B (Proc. Suppl.

Probing the neutrino mass ordering with KM3NeT-ORCA: Analysis and perspectives

The discrimination of the two possible options for the neutrino mass ordering (normal or inverted) is a major goal for current and future neutrino oscillation experiments. Such goal might be reached by observing high-statistics energy-angle spectra of events induced by atmospheric neutrinos and antineutrinos propagating in the Earth matter. Large volume water-Cherenkov detectors envisaged to this purpose include the so-called KM3NeT-ORCA project (in seawater) and the IceCube-PINGU project (in ice). Building upon a previous work focused on PINGU, we study in detail the effects of various systematic uncertainties on the ORCA sensitivity to the mass ordering, for the reference configuration with 9 m vertical spacing. We point out the need to control spectral shape uncertainties at the percent level, the effects of better priors on the theta-23 mixing parameter, and the benefits of an improved flavor identification in reconstructed ORCA events.Comment: 15 pages, including 7 figures. A few paragraphs and references added. Invited contribution to appear in the JPG Focus Issue on "Neutrino Mass and Mass Ordering

Majorana neutrino mass constraints in the landscape of nuclear matrix elements

We discuss up-to-date constraints on the Majorana neutrino mass $m_{\beta\beta}$ from neutrinoless double beta decay ($0\nu\beta\beta$) searches in experiments using different isotopes: KamLAND-Zen and EXO ($^{136}$Xe), GERDA and MAJORANA ($^{76}$Ge) and CUORE ($^{130}$Te). Best fits and upper bounds on $m_{\beta\beta}$ are explored in the general landscape of nuclear matrix elements (NME), as well as for specific NME values obtained in representative nuclear models. By approximating the likelihood of $0\nu\beta\beta$ signals through quadratic forms, the analysis of separate and combined isotope data becomes exceedingly simple, and allows to clarify various aspects of multi-isotope data combinations. In particular, we analyze the relative impact of different data in setting upper bounds on $m_{\beta\beta}$, as well as the conditions leading to nonzero $m_{\beta\beta}$ at best fit, for variable values of the NMEs. Detailed results on $m_{\beta\beta}$ from various combinations of data are reported in graphical and numerical form. Implications for future $0\nu\beta\beta$ data analyses and NME calculations are briefly discussed.Comment: 13 pages, including 6 tables and 7 figure

Neutrinos self interactions in Supernovae

Oscillations of neutrino emerging from a supernova core are studied. In this extremely high density region neutrino self interactions induce collective flavor transitions. When collective transitions are decoupled from matter oscillations, as for our chosen matter profile, an analytical interpretation of the collective effects is possible, by means of a mechanical analogy with a spherical pendulum. For inverted neutrino hierarchy the neutrino propagation can be divided in three regimes: synchronization, bipolar oscillations, and spectral split. Our simulation shows that averaging over neutrino trajectories does not alter the nature of these three regimes.Comment: 6 pages, 7 figures, to appear in the Proceedings of the 43rd Rencontres de Moriond EW session, La Thuile, Italy, 1-8 March 200

Quo vadis neutrino?

Proverò a identificare alcune possibili traiettorie della futura fisica dei neutrini, con un occhio attento soprattutto al lettore non esperto in fisica, ma semplicemente incuriosito da questo campo di ricerca. Per semplicità farò riferimento, oltre ai precedenti articoli di Ithaca sull'argomento, ad alcune voci di Wikipedia (con i loro pregi e difetti)

Quo vadis neutrino?

Proverò a identificare alcune possibili traiettorie della futura fisica dei neutrini, con un occhio attento soprattutto al lettore non esperto in fisica, ma semplicemente incuriosito da questo campo di ricerca. Per semplicità farò riferimento, oltre ai precedenti articoli di Ithaca sull'argomento, ad alcune voci di Wikipedia (con i loro pregi e difetti)

Fast flavor conversions of supernova neutrinos: Classifying instabilities via dispersion relations

Supernova neutrinos can exhibit a rich variety of flavor conversion mechanisms. In particular, they can experience "fast" self-induced flavor conversions almost immediately above the core. Very recently, a novel method has been proposed to investigate these phenomena, in terms of the dispersion relation for the complex frequency and wave number ($\omega$,$k$) of disturbances in the mean field of the $\nu_e\nu_x$ flavor coherence. We discuss a systematic approach to such instabilities, originally developed in the context of plasma physics, and based of the time-asymptotic behavior of the Green's function of the system. Instabilities are typically seen to emerge for complex $\omega$, and can be further characterized as convective (moving away faster than they spread) and absolute (growing locally), depending on $k$-dependent features. Stable cases emerge when $k$ (but not $\omega$) is complex, leading to disturbances damped in space, or when both $\omega$ and $k$ are real, corresponding to complete stability. The analytical classification of both unstable and stable modes leads not only to qualitative insights about their features but also to quantitative predictions about the growth rates of instabilities. Representative numerical solutions are discussed in a simple two-beam model of interacting neutrinos. As an application, we argue that supernova and binary neutron star mergers exhibiting a "crossing" in the electron lepton number would lead to an absolute instability in the flavor content of the neutrino gas.Comment: (v2, revised version: 25 pages, 15 pdf figures. Minor changes. Figures improved. Matches the version published on PRD

Turbulence patterns and neutrino flavor transitions in high-resolution supernova models

During the shock-wave propagation in a core-collapse supernova (SN), matter turbulence may affect neutrino flavor conversion probabilities. Such effects have been usually studied by adding parametrized small-scale random fluctuations (with arbitrary amplitude) on top of coarse, spherically symmetric matter density profiles. Recently, however, two-dimensional (2D) SN models have reached a space resolution high enough to directly trace anisotropic density profiles, down to scales smaller than the typical neutrino oscillation length. In this context, we analyze the statistical properties of a large set of SN matter density profiles obtained in a high-resolution 2D simulation, focusing on a post-bounce time (2 s) suited to study shock-wave effects on neutrino propagation on scales as small as O(100) km and possibly below. We clearly find the imprint of a broken (Kolmogorov-Kraichnan) power-law structure, as generically expected in 2D turbulence spectra. We then compute the flavor evolution of SN neutrinos along representative realizations of the turbulent matter density profiles, and observe no or modest damping of the neutrino crossing probabilities on their way through the shock wave. In order to check the effect of possibly unresolved fluctuations at scales below O(100) km, we also apply a randomization procedure anchored to the power spectrum calculated from the simulation, and find consistent results within \pm 1 sigma fluctuations. These results show the importance of anchoring turbulence effects on SN neutrinos to realistic, fine-grained SN models.Comment: 19 pages, 8 figures (Major changes in the text, references added, analysis and figures improved, main results unchanged. To appear in JCAP.