Neutrinos are fundamental particles which only interact via gravity and the weak force, which makes them uniquely hard to observe and study experimentally. There are three flavors in the Standard Model (SM) of particle physics, however there has been experimental results that suggest the existence of a theoretical fourth neutrino flavor, called the sterile neutrino, with the three flavors in the SM being active neutrinos. Sterile neutrinos would interact only via the gravity, which means we would only be able to detect them through neutrino oscillations. A potential environment in which active to sterile oscillations could be highly probable to occur is supernovae, due to a large amount of neutrinos being created through nuclear fusion as well as high and varying densities of matter through which the neutrinos propagate. To investigate the evolution of neutrinos in supernova environments and the possibility of stimulated sterile neutrino oscillations, we create a code to simulate the evolution of neutrinos through a supernova density profile.

We apply the model of stimulated neutrino transitions to neutrinos travelling through turbulence on a non constant density profile. We describe a method to predict the location of large amplitude transitions and demonstrate the effectiveness of this method by comparing to numerical calculations using a model supernova (SN) profile. The important wavelength scales of turbulence, both those that stimulate neutrino transformations and those that suppress them, are presented and discussed. We then examine the effects of changing the parameters of the turbulent spectrum, specifically the root-mean-square amplitude and cutoff wavelength, and show how the stimulated transitions model offers an explanation for the increase in both the amplitude and number of transitions with large amplitude turbulence, as well as a suppression or absence of transitions for long cutoff wavelengths. The method can also be used to predict the location of transitions between anti-neutrino states which, in the normal hierarchy we are using, will not undergo Mikheev-Smirnov-Wolfenstein transitions. Lastly, the stimulated neutrino transitions method is applied to a turbulent 2D supernova simulation and explains the minimal observed effect on neutrino oscillations in the simulation as being due to excessive long wavelength modes suppressing transitions and the absence of modes that fulfill the parametric resonance condition.

Contents:Solar Neutrinos:The Latest Solar Neutrino Results in Super-Kamiokande (Y Koshio)Weak Current in Deuterium (T Sato)Solar Neutrino Phenomenology and Future:Solar Neutrino Oscillations (M C Gonzalez-Garcia)The Status of Resonant Spin Flavor Precession (C S Lim)Atmospheric Neutrinos:Status of the Atmospheric Neutrino Studies (M D Messier)Cosmic Ray Measurements for Atmospheric Neutrino with BESS-TeV (K Abe)Oscillation Phenomenology I:Calculations of the Atmospheric ν Fluxes (P Lipari)Three-Flavor Analysis of Atmospheric and Solar Neutrinos (A Marrone)Absolute Neutrino Mass:Neutrinoless Double Beta Decay and Neutrino Oscillations (H V Klapdor-Kleingrothaus)Accelerator Neutrinos, CPV:The MINOS Experiment (M D Messier)The JHF-Kamioka Neutrino Project (T Kajita)Models and GUTs:Proton Decay in the Semi-Simple Unification Model (T Watari)Leptogenesis via LHu Flat Direction (M Fujii)Lepton Flavor Violation:Probing Physics Beyond the Standard Model from Lepton Sector (J Hisano)Oscillation Phenomenology II:Four Puzzles of Neutrino Mixing (S M Barr)Supernova Neutrinos:Supernova Neutrinos (J F Beacom)and other papers Readership: Researchers in high energy physics. Keywords:Solar Neutrinos;Atmospheric Neutrinos;Oscillation Phenomenology;Neutrino Mass;Accelerator Neutrinos;CP Violation;GUTs;Lepton Flavor Violation;Supernova Neutrinos

The discovery of neutrino oscillations in 1998 initiated efforts to form a group to work on the detailed study of the phenomenon; this study is now supported by a grant-in-aid in the specific field of neutrinos from the Japanese Ministry of Education, Culture and Sports. The aim of this working group is to put together the efforts from various fields necessary for understanding neutrino oscillations in detail from both the experimental and the theoretical point of view. The 4th International Workshop on Neutrino Oscillations and Their Origin was held to discuss recent progress in both experimental and theoretical study.

This volume brings together international experts in diverse areas of physics to discuss recent progress in the experimental and theoretical study of neutrino oscillations.Readers are brought up to date with the latest developments in important neutrino experiments, and the associated progress in theory is summarized. The principal projects worldwide, such as Super-Kamiokande, SNO, KamLAND, are considered, and contributions also report on future experiments, including JPARC, OPERA, and MINOS.Several other related topics, such as dark matter, double beta decay, lepton flavor violation, and cosmology, are discussed, reflecting the wide-ranging specializations of many contributors outside of pure neutrino physics.