PrefaceNeutrinos have played a key role in the evolution of our understanding of particles, forces and the universe and most likely the next step in this process of exploration of physics beyond the standard model will come from new properties of the neutrino revealed in many on going experiments such as the solar neutrino experiments, neutrino mass mea surements, double beta decay searches etc. In the absence of any solid experimental clues regarding this new direction, many interesting the oretical speculations have been advanced with implications for collider as well as non-collider experiments. The central theme of most of these speculations in the possibility of a massive neutrino which in turn im pacts on our thinking about the universe past and present. Most of these ideas will be put to test by the same kind of experiments discussed.We therefore felt that it may be an appropriate time to summarize the theoretical, phenomenological and astrophysical implications of the massive neutrino so that first, a person starting out in the field will have a ready reference to the major existing ideas and, secondly, an expert in the field may be spared frequent trips to the library to clarify simple points in bis or her thinking. In this spirit, we have not attempted a complete, exhaustive survey of all the details in various areas of neu trino physics but rather an introduction to the important major ideas in the field. We have tried to restrain our personal prejudices in the pre sentation to the extent humanly possible. We have most certainly left out some ideas as we must have missed citing some important works. While some of it is perhaps unavoidable because of the size of the book, mostly it is inadvertant and will be included in subsequent editions if brought to our attention with sufficient conviction. We have, however, given references to review articles where additional references can be vii A suggestion for new comers to the area trying to read this book : a necessary pre-requisite is a course on field theory, group theory and basic concepts in particle physics, and a right attitude. We have added some exercises at the end of the book to help the new comers. Our notations regarding the metric and gamma matrices etc are the same as the stan dard text books on Quantum Field theory such as the book by Bjorken and Drell or by Itzykson and Zuber, with the following comments or exceptions:• Our normalization of spinor solutions to Dirac equation is different.It has been described in §4.3 and has the advantage that it applies equally well to massive as well as massless fields.• To denote antiparticles, we do not use the customary bar since it is easy to confuse it with the operation of hermitian conjugation followed by multiplication of the Dirac matrix 7 0 . Neither do we use the notation, which is used in some modern literature, of attaching a superscript c to the particle since it might lead to the misconception that the antiparticle is the C conjugate of the particle. For particles like the neutrinos whose int...

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We consider the breaking of the grand unification group SO(10) to the standard model gauge group through several chains containing one intermediate breaking scale. Using the values of the gauge coupling constants at the scale M z derived from recent data from the CERN ef e-collider LEP, we determine the intermediate and the unification scales using two-loop renormalization group equations with appropriate matching conditions. Some chains are ruled out from experimental constraints. For the allowed ones, the intermediate scale is high, in the range of 1 0~-1 0~~ GeV. PACS number(s): 12.10.Dm, 12.15.C~ Recently it has been emphasized [I, 21 that the precision of data from the CERN e+e-collider LEP allows the extraction of the three coupling constants of the standard model very accurately, and this enables an extrapolation to high energies with very small errors. In these papers it was shown that if one extrapolates the couplings without change of particle content (i.e., with three families of fermions and one doublet of Higgs boson) or the group structure in the intervening energy scale, these couplings do not come together at a single point. Although this result is not unexpected, the statistical significance has been greatly improved. For example, LEP data imply [3] where cui = g:/4~, and gl, gz, 93 denote the normalized gauge coupling constants for the U(l)y, S U (~) L , and SU(3), factors, respectively. Now, if we take the central values for crl and a 2 , we need cr,(Mz) cz 0.07 in order to achieve unification. This is more than seven standard deviations removed from the mean value.In Refs.[I] and [2] it was further pointed out that the minimal supersymmetric model, with the supersymmetry-breaking scale MsusY N

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