Flavor-changing Neutrino Research Articles

Astrophysical neutrino telescopes

This review describes telescopes designed to study neutrinos from astrophysical sources. These sources include the sun and supernovae emitting neutrino energies up to tens of MeV, atmospheric neutrino sources caused by cosmic ray interactions, and other sources generating neutrino energies ranging up to 1×1020 eV. Measurements with these telescopes also provide information on neutrino properties, including clear evidence for neutrino flavor change. Telescopes in operation in the past and present are described, along with plans for future instruments to expand this rapidly growing field of particle astrophysics.

Flavor Changing Neutrino Interactions and CP Violation in Neutrino Oscillations

We investigate the interference effects of non-standard neutrino-matter interactions (NSNI) with the mass-induced neutrino oscillations. The NSNI is composed of flavor-changing neutrino interactions (FCNI) and flavor-diagonal neutrino interactions (FDNI). Both of the interactions are introduced in the \nu_\mu -\nu_\tau sector and the \nu_e -\nu_\mu sector in order to study their effects in \nu_\mu\to\nu_\tau and \nu_\mu\to\nu_e oscillations, respectively. The FCNI effect proves to possibly dominate the CP violating effect and significantly survive as a fake CP violating effct in the neutrino energy region where the pure CP violating effect, ordinary matter effect and FDNI effect fall, for example, above 4 GeV at the baseline of L=730 km in the \nu_\mu\to\nu_\tau oscillation for the maximum parameter values of FCNI and FDNI allowed by the atmospheric neutrino oscillation data. The FCNI and FDNI effects on CP violation in the $\nu_\mu\to\nu_e$ oscillation are negligibly small due to the stringent constraints on FCNI from the bounds on lepton flavor violating processes and on FDNI from the limits on lepton universality violation.

Solar Neutrino measurements

This paper discusses present results and future measurements of solar neutrinos by experiments presently in operation, including Homestake, Sage, Gallex, Kamiokande, Superkamiokande and SNO. The results to date, including both solar model dependent and independent measurements indicate that solar electron neutrinos are changing to other active types and that transitions solely to sterile neutrinos are disfavored. The initial flux of 8 B solar neutrinos is found to be in very good agreement with solar model calculations. Future measurements will focus on greater accuracy for experiments sensitive to low neutrino energies as well as charged current and neutral current sensitive reactions to provide more accurate measurements of neutrino flavour change and further studies of day-night flux differences and spectral shape. These future results are expected to define the parameters for solar neutrino flavor change and initial solar fluxes with much better accuracy.

Future tests of non-standard neutrino interactions

We explore non-standard neutrino matter interactions, working as sub-leading effects in the standard mass oscillation framework. Both mechanisms working together, induce a magnifying fake CP violating effect in the presence of matter, which can be studied in a neutrino factory which is based on a muon storage ring. Considering the three neutrino scheme, assuming a 10 kt detector with 5 years of operation, a stored muon energy Eμ ≥ 20 GeV, 2 × 10 20 muon decays per year, and a baseline L ∼ 732 km, we show that it is possible to test non-standard flavor changing neutrino interactions down to the level of (10 −3−10 −2) G F , in both ν μ å ν τ/ ν τ → ν τ and ν e → ν τ/ ν e modes.

Updated solution to the solar neutrino problem based on non-standard neutrino interactions

We present an updated version of the solution to the solar neutrino problem based on non-standard flavor changing neutrino interactions (FCNI) and non-universal flavor diagonal neutrino interactions (FDNI). We find a good fit not only to the total rates measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration.

Status of the solution to the solar neutrino problem based on non-standard neutrino interactions

We analyze the current status of the solution to the solar neutrino problem based both on: a) non-standard flavor changing neutrino interactions (FCNI) and b) non-universal flavor diagonal neutrino interactions (FDNI). We find that FCNI and FDNI with matter in the sun as well as in the earth provide a good fit not only to the total rate measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration. This solution does not require massive neutrinos and neutrino mixing in vacuum. Stringent experimental constraints on FCNI from bounds on lepton flavor violating decays and on FDNI from limits on lepton universality violation rule out ν e → ν μ transitions induced by New Physics as a solution to the solar neutrino problem. However, a solution involving ν e → ν τ transitions is viable and could be tested independently by the upcoming B-factories if flavor violating tau decays would be observed at a rate close to the present upper bounds.

Status of the solution to the solar neutrino problem based on nonstandard neutrino interactions

We analyze the current status of the solution to the solar neutrino problem based both on: a) non-standard flavor changing neutrino interactions (FCNI) and b) non-universal flavor diagonal neutrino interactions (FDNI). We find that FCNI and FDNI with matter in the sun as well as in the earth provide a good fit not only to the total rate measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration. This solution does not require massive neutrinos and neutrino mixing in vacuum. Stringent experimental constraints on FCNI from bounds on lepton flavor violating decays and on FDNI from limits on lepton universality violation rule out $\nu_e \to \nu_\mu$ transitions induced by New Physics as a solution to the solar neutrino problem. However, a solution involving $\nu_e \to \nu_\tau$ transitions is viable and could be tested independently by the upcoming $B$-factories if flavor violating tau decays would be observed at a rate close to the present upper bounds.

Can lepton flavor violating interactions explain the atmospheric neutrino problem?

We investigate whether flavor changing neutrino interactions (FCNIs) can be sufficiently large to provide a viable solution to the atmospheric neutrino problem. Effective operators induced by heavy boson exchange that allow for flavor changing neutrino scattering off quarks or electrons are related by an $SU(2)_L$ rotation to operators that induce anomalous tau decays. Since $SU(2)_L$ violation is small for New Physics at or above the weak scale, one can use the upper bounds on lepton flavor violating tau decays or on lepton universality violation to put severe, model-independent bounds on the relevant non-standard neutrino interactions. Also $Z$-induced flavor changing neutral currents, due to heavy singlet neutrinos, are too small to be relevant for the atmospheric neutrino anomaly. We conclude that the FCNI solution to the atmospheric neutrino problem is ruled out.

Solutions to the atmospheric neutrino problem

In this talk I review the present status of the atmospheric neutrino anomaly and discuss some solutions that have been presented in the literature to solve this problem. In particular I will review the “standard” solution in terms of neutrino oscillations as well as alternative scenarios such as the possibility of flavour changing neutrino interactions with the Earth and neutrino decay.

The sudbury neutrino observatory project

The construction of the Sudbury Neutrino Observatory (SNO) project was completed in April, 1998 and the detector is presently in operation as it is being filled with light and heavy water. The SNO detector is a 1,000 tonne heavy water Cerenkov detector situated 2,000 meters underground in INCO's Creighton Mine near Sudbury, Ontario, Canada. [1] The project is a Canadian, US and UK collaboration. Through the use of heavy water SNO will be able to detect a number of neutrino reactions, including one sensitive specifically to electron neutrinos and another one which is sensitive to all neutrino types. With these two reactions the detector will be used to search for solar neutrino flavour change without the requirement of electron neutrino flux normalization by solar model calculations. It will also provide unusual sensitivity for other measurements of solar neutrino properties, atmospheric neutrinos and supernova neutrinos.

Atmospheric Neutrino Observations and Flavor Changing Interactions

Flavor changing (FC) neutrino-matter interactions can account for the zenith-angle-dependent deficit of atmospheric neutrinos observed in the SuperKamiokande experiment, without directly invoking either neutrino mass or mixing. We find that FC ${\ensuremath{\nu}}_{\ensuremath{\mu}}$-matter interactions provide a good fit to the observed zenith angle distributions, comparable in quality to the neutrino oscillation hypothesis. The required FC interactions arise naturally in many attractive extensions of the standard model.

The solar neutrino problem in the presence of flavor-changing neutrino interactions

We study the effects of flavor-changing neutrino interactions on the resonant conversion of solar neutrinos. In particular, we describe how the regions in the Δm2−sin22δ plane that are consistent with the four solar neutrino experiments are modified for different strengths of New Physics neutrino interactions.

Resonant enhancement of flavor-changing neutrino interactions

The resonant amplification of neutrino oscillations in the presence of flavor-changing neutrino interactions with matter is analyzed. It is shown that a significant {mu}-flavor conversion can take place even in the absence of neutrino mixing in vacuum. To account for the solar neutrino deficit, the strength of the new interactions should be {approximately} 10{sup {minus}2}G{sub F} and the resulting neutrino suppression and spectrum is similar to that in the ordinary MSW effect. I discuss some extensions of the standard model where these interactions can be present, taking into account the experimental constraints that arise mainly from the induced leptonic rare decays.

Mikheyev-Smirnov-Wolfenstein effect with flavor-changing neutrino interactions.

We consider the effect that flavor-nondiagonal neutrino interactions with matter have on the resonant {nu} oscillations. It is shown that, even in the absence of {nu} mixing in a vacuum, an efficient conversion of the electron neutrinos from the Sun to another {nu} flavor can result if the strength of this interaction is {similar to}10{sup {minus}2}{ital G}{sub {ital F}}. We show how this can be implemented in the minimal supersymmetric standard model with {ital R}-parity breaking. Here, the {ital L}-violating couplings induce neutrino masses, mixings, and the flavor-nondiagonal neutrino interactions that can provide a Mikheyev-Smirnov-Wolfenstein-like solution to the solar-neutrino problem even for negligible vacuum mixings.

Massive neutrinos and the weak scale singlet majoron

We consider the phenomenology of the singlet majoron model of Chikashige, Mohapatra and Peccei in the case where lepton number is broken at the weak scale. This scenario naturally leads to a see-saw mechanism for the neutrino masses in which the light neutrinos are close to their experimental limits. A fourth generation can also be incorporated in a natural way. We argue that this model is compatible with all experimental, astrophysical, and cosmological constraints at present, but can be stringently tested by experiments in the near future. First, we show that the rates for flavor-changing neutrino decays into majorons in this model can evade cosmological limits. Second, we consider the “triviality” bounds for the case in which the symmetry is broken by light scalars, and show that these are much more stringent for this model than for the standard model. Third, we consider majoron production through couplings to the electroweak symmetry breaking sector, both for the case in which the symmetries are broken by light scalars and for a non-linear realization of the broken symmetry. For the scalar case, we find that much of the parameter space of the model can be probed by collider and rare decay experiments in the near future. For the non-linear case, we find that the cross section for majoron production is probably too small to be observed at the SSC, even under rather optimistic theoretical assumptions. However, in this case, we argue that the scale of new physics is well below SSC energies, so that there would be a good chance of seeing new physics at the SSC.

Resonant amplification of neutrino spin rotation in matter and the solar-neutrino problem

It is shown that in the presence of matter there can occur resonant amplification of the flavor-changing neutrino spin rotation in transverse magnetic fields, which is roughly analogous to the Mikheyev-Smirnov-Wolfenstein effect in neutrino oscillations. Possible consequences for solar neutrinos are briefly discussed.

Constraints on the mass of muon neutrinos and their possible role in the galaxy formation

A lower bound is derived on the mass of muon neutrinos [ m ν μ ⪆0(1 keV ) ] by a combined use of a variety of neutrino mass experiments. Consistency with the cosmological mass density implies the presence of a flavour changing neutrino current with a symmetry breaking parameter (ν) smaller than 10 11 GeV. Further consistency with the galaxy formation sets the parameters to be in a very narrow range near m ν μ ∼ O (1keV) and ν ∼ O (10 10 GeV), for which the visible mass of galaxies that can be reached is of order M vis ∼ 10 9 - 10 11 M .