Reviews the current state of knowledge of neutrino masses and the related question of neutrino oscillations. After an overview of the theory of neutrino masses and mixings, detailed accounts are given of the laboratory limits on neutrino masses, astrophysical and cosmological constraints on those masses, experimental results on neutrino oscillations, the theoretical interpretation of those results, and theoretical models of neutrino masses and mixings. The book concludes with an examination of the potential of long-baseline experiments. This is an essential reference text for workers in elementary-particle physics, nuclear physics, and astrophysics.

For many years neutrino was considered a massless particle. The theory of a two-componentneutrino,whichplayedacrucialroleinthecreationofthetheoryof theweakinteraction,isbasedontheassumptionthattheneutrinomassisequalto zero. We now know that neutrinos have nonzero, small masses. In numerous exp- iments with solar, atmospheric, reactor and accelerator neutrinos a new p- nomenon, neutrino oscillations, was observed. Neutrino oscillations (periodic transitionsbetweendifferent?avorneutrinos? ,? ,? )arepossibleonlyifneutrino e ? ? mass-squareddifferencesaredifferentfromzeroandsmalland?avorneutrinosare “mixed”. The discovery of neutrino oscillations opened a new era in neutrino physics: an era of investigation of neutrino masses, mixing, magnetic moments and other neutrino properties. After the establishment of the Standard Model of the el- troweak interaction at the end of the seventies, the discovery of neutrino masses was the most important discovery in particle physics. Small neutrino masses cannot be explained by the standard Higgs mechanism of mass generation. For their explanation a new mechanism is needed. Thus, small neutrino masses is the ?rst signature in particle physics of a new beyond the Standard Model physics. It took many years of heroic efforts by many physicists to discover n- trino oscillations. After the ?rst period of investigation of neutrino oscillations, manychallengingproblemsremainedunsolved.Oneofthemostimportantisthe problem of the nature of neutrinos with de?nite masses. Are they Dirac n- trinos possessing a conserved lepton number which distinguish neutrinos and antineutrinos or Majorana neutrinos with identical neutrinos and antineutrinos? Many experiments of the next generation and new neutrino facilities are now under preparation and investigation. There is no doubt that exciting results are ahead.

The neutrino is the most fascinating elementary particle due to its elusive nature and outstanding properties that have attracted the interest of generations of physicists since 1930, when it was first postulated by Wolfgang Pauli as a 'desperate remedy' to explain the apparent energy violation in the beta decay. Many fundamental discoveries in particle physics had the neutrino involved in one way or another. To date, neutrino physics is still one of the hottest topics of modern particle physics. Key experiments and significant theoretical developments have contributed in building up what we can call now the Standard Model of Neutrino Physics.The aim of the book is to provide graduate students and young researchers a comprehensive tutorial in modern neutrino physics, specially tailored with emphasis on the educational aspects. It provides an overview of the basics and of recent achievements in the field, from both experimental and theoretical points of view.

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

Contents: Status and Future Prospects of Reactor Neutrinos, Solar Neutrinos, and Supernova Neutrinos; Status and Future Prospects of Long Baseline Neutrino Experiments, Atmospheric Neutrinos; Dark Matter Searches and Double Beta Decays; Lepton Number Violated Muon Decays; Proton Decay Searches; Neutrino Phenomenology and Model Building.

Our Universe is made of a dozen fundamental building blocks. Among these, neutrinos are the most mysterious - but they are the second most abundant particles in the Universe. This book provides detailed discussions of how to describe neutrinos, their basic properties, and the roles they play in nature.

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.