Neutrinoless Double Beta Decay and Physics Beyond the Standard Model

The various mechanisms for neutrinoless double beta decay in gauge theories are reviewed and the present experimental data is used to set limits on physics scenarios beyond the standard model. The positive indications for nonzero neutrino masses in various experiments such as those involving solar, atmospheric and accelerator neutrinos are discussed and it is pointed out how some neutrino mass textures consistent with all data can be tested by the ongoing double beta decay experiments. Finally, the outlook for observable neutrinoless double beta decay signal in grand unified theories is discussed.Comment: 21 pages, latex; 10 figures available on request; Invited talk presented at the "International Workshop on Neutrinoless Double Beta Decay and relate topics", Trento, Italy; April, 1995; to appear in the proceedings to be published by World scientifi

Gauged Flavor, Supersymmetry and Grand Unification

I review a recent work on gauged flavor with left-right symmetry, where all masses and all Yukawa couplings owe their origin to spontaneous flavor symmetry breaking. This is suggested as a precursor to a full understanding of flavor of quarks and leptons. An essential ingredient of this approach is the existence of heavy vector-like fermions, which is the home of flavor, which subsequently gets transmitted to the familiar quarks and leptons via the seesaw mechanism. I then discuss implications of extending this idea to include supersymmetry and finally speculate on a possible grand unified model based on the gauge group $SU(5)_L\times SU(5)_R$ which provides a group theoretic origin for the vector-like fermions.Comment: Invited talk at the GUT 2012 workshop held in Kyoto, Japan in March, 201

Physics of Neutrino Mass

Recent discoveries in the field of neutrino oscillations have provided a unique window into physics beyond the standard model. In this lecture, I summarize how well we understand the various observations, what they tell us about the nature of new physics and what we are likely to learn as some of the planned experiments are carried out.Comment: Invited Lecture at the SLAC Summer Institute, August, 2004; 23 pages, 6 figure

Understanding the Standard Model

We explore to what extent the various assumptions behind the standard model as well as the observed quantization of electric charges of quarks and leptons can be understood using the Adler-Bell-Jackiw anomalies. The effect of including a non-zero neutrino mass on these considerations is also discussed.Comment: University of Maryland Report No. UMD-PP-94-116; To be published in the Robert E. Marshak memorial volume, edited by George Sudarshan. ( plain Tex; 17 pages

Sterile Neutrinos: Phenomenology and Theory

A sterile neutrino in addition to the three known neutrinos seems unavoidable if one wants a simultaneous understanding of the results of the LSND experiment indicating $\nu_{\mu}-\nu_e$ oscillation together with other evidences for neutrino oscillations such as those from solar and atmospheric neutrino deficits. A major theoretical challenge then is to understand why the sterile neutrino is so light. A simple solution appears to be to assume that it is the lightest neutrino of a mirror sector of the universe which has identical matter and gauge content as the standard model. After a brief review of the phenomenology, a recently constructed realistic grand unified model based on the gauge group $SO(10)\times SO(10)^\prime$ that embeds the mirror universe idea is presented. Detailed predictions for known and the sterile neutrino sector are given and their consequences for cosmology are mentioned.Comment: Invited talk presented at the workshop on "New trends in neutrino physics" held at the Ringberg Castle, Germany, May 24-28, 1998; 10 page