C. W. Kim

Treatment of neutrino oscillations without resort to weak eigenstates

We discuss neutrino oscillations in the framework of the quantum field theory without introducing the concept of neutrino weak eigenstates. The external particles are described by wave packets and the different mass eigenstate neutrinos propagate between the production and detection interactions, which are macroscopically localized in space-time. The time-averaged cross section, which is the measurable quantity in the usual experimental setting, is calculated. It is shown that only in the extremely relativistic limit can the usual quantum mechanical oscillation probability be factored out of the cross section.

Supersymmetric neutrino masses and mixing with R-parity violation

In the context of the minimal supersymmetric standard model, non-zero neutrino masses and mixing can be generated through renormalizable lepton number (and thus R-parity) violating operators. It is examined whether neutrino mass matrices from tree and one-loop contributions can account for two mass-squared differences and mixing angles that explain current experimental data. By accommodating, in particular, the solar and atmospheric neutrino data, we find interesting restrictions not only on the free parameters of the theory, such as lepton number violating couplings and soft parameters, but also on the oscillation parameters of atmospheric neutrinos.

Coherence of neutrino oscillations in the wave packet approach

The temporal and spatial coherence widths of the microscopic process by which a neutrino is detected are incorporated in the quantum mechanical wave packet treatment of neutrino oscillations, confirming the observation of Kiers, Nussinov and Weiss that an accurate measurement of the energies of the particles participating in the detection process can increase the coherence length. However, the wave packet treatment presented here shows that the coherence length has an upper bound, determined by the neutrino energy and the mass-squared difference, beyond which the coherence of the oscillation process is lost.

Short-baseline neutrino oscillations and ( beta beta )0 nu decay in schemes with an inverted mass spectrum.

We have considered short-baseline neutrino oscillations, tritium beta-decay and neutrinoless double-beta decay in two schemes with an inverted mass spectrum and mixing of three and four massive neutrino fields. We have analyzed the results of the latest experiments on the search for oscillations of terrestrial neutrinos and we have discussed the compatibility of the LSND indication in favor of neutrino oscillations with the results of the other experiments. In the framework of the models under consideration, it is shown that the observation of neutrinoless double-beta decay could allow to obtain information about the CP violation in the lepton sector.

Gravitational effects on the neutrino oscillation

The propagation of neutrinos in a gravitational field is studied. A method of calculating a covariant quantum-mechanical phase in a curved space-time is presented. The result is used to calculate gravitational effects on the neutrino oscillation in the presence of a gravitational field. We restrict our discussion to the case of the Schwarzschild metric. Specifically, the cases of the radial propagation and the nonradial propagation are considered. A possible application to gravitational lensing of neutrinos is also suggested. {copyright} {ital 1997} {ital The American Physical Society}

Quantum Mechanics of Neutrino Oscillations

We present a simple but general treatment of neutrino oscillations in the framework of quantum mechanics, using plane waves and intuitive wave packet principles when necessary. We attempt to clarify some confusing statements that have recently appeared in the literature.

Matter effects in four-neutrino mixing

The evidence in favor of neutrino oscillations implies the existence of at least three independent neutrino mass-squared differences. If the Liquid Scintillation Neutrino Detector (LSND) results are confirmed, transitions into active and sterile neutrinos can take place simultaneously for both solar and atmospheric neutrinos. In this paper we present a formalism for the calculation of the transition probabilities into active and sterile neutrinos for solar {nu}{sub e}s and atmospheric {nu}{sub {mu}}s, taking into account the matter effects in the Sun and in the Earth. We find that the solar neutrino transition probabilities depend on just one single additional parameter compared to that of the standard two-generation analysis, while for atmospheric neutrinos two additional mixing angles are necessary to analyze the data in addition to those of the usual two-generation analysis. (c) 2000 The American Physical Society.

When do neutrinos cease to oscillate

Abstract In order to investigate when neutrinos cease to oscillate in the framework of quantum field theory, we have reexamined the wave packet treatment of neutrino oscillations by taking different sizes of the wave packets of the particles involved in the production and detection processes. The treatment is shown to be considerably simplified by using the Grimus–Stockinger theorem which enables us to carry out the integration over the momentum of the propagating neutrino. Our new results confirm the recent observation by Kiers, Nussinov and Weiss that a precise measurement of the energies of the particles involved in the detection process would increase the coherence length. We also present a precise definition of the coherence length beyond which neutrinos cease to oscillate.

Neutrino self-energy and dispersion in a medium with a magnetic field

We calculate the one-loop thermal self-energy of a neutrino in a constant and homogeneous magnetic field to all orders in the magnetic field strength using Schwingers proper time method. We obtain the dispersion relation under various conditions.

Coherence of neutrino oscillations in vacuum and matter in the wave packet treatment

We present a geometrical representation of neutrino oscillations in vacuum and matter in which a propagating neutrino is described by a superposition of mass-eigenstate wave packets (energy-eigenstate wave packets in matter). The effect of the coherence length (that is the distance beyond which the wave packets separate) in the MSW effect is illustrated by using the solar neutrinos as an example. It is shown that, if the coherence length is shorter than the size of the resonance region, non-adiabatic MSW transitions become increasingly adiabatic as the coherence length is decreased.