Test of non-standard neutrino properties with the BOREXINO source experiments

We calculate the event rates induced by high-intensity radioactive sources of nu_e (51Cr) and of anti-nu_e (90Sr), to be located near the BOREXINO detector. Calculations are performed both in the standard case and assuming non-standard properties of neutrinos, including flavor oscillations, neutrino electromagnetic interactions, and deviations from the standard vector and axial couplings in the nu_e-e interaction. It is shown that, in some cases, the current limits on non-standard neutrino properties can be significantly improved.Comment: 15 pages (RevTeX) + 4 figures (postscript) included with epsfig.sty. Minor changes and corrections, 3 references added. Final version to be published in Europ. Phys. Jour.

Addendum to: Model-dependent and -independent implications of the first Sudbury Neutrino Observatory results

In the light of recent experimental and theoretical improvements, we review our previous model-independent comparison [hep-ph/0106247] of the Super-Kamiokande (SK) and Sudbury Neutrino Observatory (SNO) solar neutrino event rates, including updated values for the ``equalized'' SK datum and for the reference Standard Solar Model (SSM) B neutrino flux. We find that the joint SK+SNO evidence for active neutrino flavor transitions is confirmed at the level of 3.3 standard deviations, independently of possible transitions to sterile states. Barring sterile neutrinos, we estimate the 3-sigma range for the $^8$B neutrino flux (normalized to SSM) as f_B=0.96 +0.54-0.55. Accordingly, the 3-sigma range for the energy-averaged nu_e survival probability is found to be = 0.31 +0.55-0.16, independently of the functional form of P_ee. An increase of the reference nu_e + d --> p + p + e cross section by ~3%, as suggested by recent theoretical calculations, would slightly shift the central values of f_B and of to ~1.00 and ~0.29, respectively, and would strengthen the model-independent evidence for nu_e transitions into active states at the level of ~3.6 sigma.Comment: 6 pages + 2 figures. Addendum to hep-ph/010624

Probing neutrino magnetic moment and unparticle interactions with Borexino

We discuss the limits on the neutrino magnetic moment and hypothetical interactions with a hidden unparticle sector, coming from the first neutrino data release of the Borexino experiment. The observed spectrum in Borexino depends weakly on the solar model used in the analysis, since most of the signal comes from the mono-energetic 7Be neutrinos. This fact allows us to calibrate the nu-e scattering cross section through the spectral shape. In this way, we have derived a limit on the magnetic moment for the neutrinos coming from the Sun (in which a nu_mu and nu_tau component is present): mu_nu<8.4E-11 mu_B (90%CL) which is comparable with those obtained from low energy reactor experiments. Moreover, we improve the previous upper limit on magnetic moment of the nu_tau by three orders of magnitude and the limit on the coupling constant of the neutrino with a hidden unparticle sector.Comment: 16 pages, 3 figures. Some clarifications and references added. Accepted for publication in Phys. Rev.

Atmospheric, Solar, and CHOOZ neutrinos: a global three generation analysis

We perform a global three generation analysis of the current solar and atmospheric evidence in favor of neutrino oscillations. We also include the negative results coming from CHOOZ to constrain the nu_e mixing. We study the zones of mass-mixing oscillations parameters compatible with all the data. It is shown that almost pure nu_mu nu_tau oscillations are required to explain the atmospheric neutrino anomaly and almost pure nu_1 nu_2 oscillations to account for the solar neutrino deficit.Comment: 4 pages, talk given at 36th Rencontres de Moriond: Electroweak Interactions and Unified Theories, Les Arcs, France, 10-17 Mar 200

Revisiting cosmological bounds on radiative neutrino lifetime

Neutrino oscillation experiments and direct bounds on absolute masses constrain neutrino mass differences to fall into the microwave energy range, for most of the allowed parameter space. As a consequence of these recent phenomenological advances, older constraints on radiative neutrino decays based on diffuse background radiations and assuming strongly hierarchical masses in the eV range are now outdated. We thus derive new bounds on the radiative neutrino lifetime using the high precision cosmic microwave background spectral data collected by the Far Infrared Absolute Spectrophotometer instrument on board of Cosmic Background Explorer. The lower bound on the lifetime is between a few x 10^19 s and 5 x 10^20 s, depending on the neutrino mass ordering and on the absolute mass scale. However, due to phase space limitations, the upper bound in terms of the effective magnetic moment mediating the decay is not better than ~ 10^-8 Bohr magnetons. We also comment about possible improvements of these limits, by means of recent diffuse infrared photon background data. We compare these bounds with pre-existing limits coming from laboratory or astrophysical arguments. We emphasize the complementarity of our results with others available in the literature.Comment: 7 pages, 3 figures. Minor changes in the text, few references added. Matches the published versio

Analysis of energy- and time-dependence of supernova shock effects on neutrino crossing probabilities

It has recently been realized that supernova neutrino signals may be affected by shock propagation over a time interval of a few seconds after bounce. In the standard three-neutrino oscillation scenario, such effects crucially depend on the neutrino level crossing probability P_H in the 1-3 sector. By using a simplified parametrization of the time-dependent supernova radial density profile, we explicitly show that simple analytical expressions for P_H accurately reproduce the phase-averaged results of numerical calculations in the relevant parameter space. Such expressions are then used to study the structure of P_H as a function of energy and time, with particular attention to cases involving multiple crossing along the shock profile. Illustrative applications are given in terms of positron spectra generated by supernova electron antineutrinos through inverse beta decay.Comment: Major changes both in the text and in the figures in order to include the effect of a step-like shock front density profile; final version to appear in Physical Review

Zenith distribution of atmospheric neutrino events and electron neutrino mixing

Assuming atmospheric neutrino oscillations with dominant nu_munu_tau transitions, we discuss how subdominant nu_e mixing (within the Chooz reactor bounds) can alter the zenith distributions of neutrino-induced electrons and muons. We isolate two peculiar distortion effects, one mainly related to nu_e mixing in vacuum and the other to matter oscillations, that may be sufficiently large to be detected by the SuperKamiokande atmospheric nu experiment. These effects (absent for pure two-flavor nu_munu_tau transitions) do not vanish in the limit of energy-averaged oscillations.Comment: 6 pages, RevTeX, no figure

Can unstable relics save pure Cold Dark Matter?

The standard CDM model fails to describe the power spectrum of fluctuations since it gives too much power at small scales. Among other possible improvements, it has been suggested that an agreement with observations can be achieved with the addition of a late decaying particle, through the injection of non-thermal radiation and the consequent increase of the horizon length at the equivalence time. We analyze the possibility of implementing this idea in extensions of the electroweak standard model, with particular attention to supersymmetry with and without R-parity. After considering cosmological and astrophysical bounds, only few candidate models survive as viable solutions

Probing supernova shock waves and neutrino flavor transitions in next-generation water-Cherenkov detectors

Several current projects aim at building a large water-Cherenkov detector, with a fiducial volume about 20 times larger than in the current Super-Kamiokande experiment. These projects include the Underground nucleon decay and Neutrino Observatory (UNO) in the Henderson Mine (Colorado), the Hyper-Kamiokande (HK) detector in the Tochibora Mine (Japan), and the MEgaton class PHYSics (MEMPHYS) detector in the Frejus site (Europe). We study the physics potential of a reference next-generation detector (0.4 Mton of fiducial mass) in providing information on supernova neutrino flavor transitions with unprecedented statistics. After discussing the ingredients of our calculations, we compute neutrino event rates from inverse beta decay ($\bar\nu_e p\to e^+ n$), elastic scattering on electrons, and scattering on oxygen, with emphasis on their time spectra, which may encode combined information on neutrino oscillation parameters and on supernova forward (and possibly reverse) shock waves. In particular, we show that an appropriate ratio of low-to-high energy events can faithfully monitor the time evolution of the neutrino crossing probability along the shock-wave profile. We also discuss some background issues related to the detection of supernova relic neutrinos, with and without the addition of gadolinium.Comment: Revised version (27 pages, 13 eps figures), to appear in JCAP. Includes revised numerical estimates and figures. In particular: calculations of inverse beta decay event rates improved by using the differential cross section by Vissani and Strumia (astro-ph/0302055); supernova relic neutrino flux calculations updated by using recent GALEX Mission data (astro-ph/0411424) on the star formation rate (SFR). References added. Conclusions unchange