Probing grand unification with fermion masses, neutrino oscillations and proton decay

Pramana ◽  
2003 ◽  
Vol 60 (2) ◽  
pp. 291-336
Author(s):  
Jogesh C. Pati
Keyword(s):  
Neutrino Oscillations ◽  
Proton Decay ◽  
Grand Unification ◽  
Fermion Masses

scholarly journals Advantages of unity with SU(4)-color: Reflections through neutrino oscillations, baryogenesis and proton decay

2017 ◽  
Vol 32 (09) ◽  
pp. 1741013 ◽  
Author(s):  
Jogesh C. Pati
Keyword(s):  
Particle Physics ◽  
Neutrino Oscillations ◽  
Gauge Coupling ◽  
High Sensitivity ◽  
Proton Decay ◽  
Charge Ratio ◽  
Grand Unification ◽  
Large Set ◽  
Minimal Extension ◽  
Seesaw Mechanism

By way of paying tribute to Abdus Salam, I first recall the ideas of higher unification which the two of us introduced in 1972–73 to remove certain shortcomings in the status of particle physics prevailing then, and then present their current role in theory as well as experiments. These attempts initiated the idea of grand unification and provided the core symmetry-structure [Formula: see text]-color towards such a unification. Embodied with quark-lepton unification and left-right symmetry, the symmetry [Formula: see text] is uniquely chosen as being the minimal one that permits members of a family to belong to a single multiplet. The minimal extension of [Formula: see text] to a simple group is given by the attractive SO(10)-symmetry that was suggested a year later. The new concepts, and the many advantages introduced by this core symmetry (which are, of course, retained by SO(10) as well) are noted. These include explanations of the observed: (i) (rather weird) electroweak and color quantum numbers of the members of a family; (ii) quantization of electric charge; (iii) electron-proton charge-ratio being [Formula: see text]; (iv) the co-existence of quarks and leptons; (v) likewise that of the three basic forces — the weak, electromagnetic and strong; (vi) the non-trivial cancelation of the triangle anomalies within each family; and opening the door for (vii) the appealing concept of parity being an exact symmetry of nature at the fundamental level. In addition, as a distinguishing feature, both because of SU(4)-color and independently because of [Formula: see text] as well, the symmetry [Formula: see text] introduced, to my knowledge, for the first time in the literature: (viii) a new kind of matter — the right-handed (RH) neutrino [Formula: see text] — as a compelling member of each family, and together with it; (ix) (B-L) as a local symmetry. The RH neutrions — contrary to prejudices held in the 1970’s against neutrinos being massive and thereby against the existence of [Formula: see text]’s as well — have in fact turned out to be an asset. They are needed to (a) understand naturally the tiny mass-scales observed in neutrino oscillations by combining the seesaw mechanism together with the unification ideas based on the symmetry SU(4)-color, and also (b) to implement the attractive mechanism of baryogenesis via leptogenesis. The quantitative success of the attempts as regards understanding both (a) and (b) are discussed in Sec. 6. These provide a clear support simultaneously for the following three features: (i) the seesaw mechanism, (ii) the SU(4)-color route to higher unification based on a symmetry like SO(10) or a string-derived [Formula: see text] symmetry in 4D, as opposed to alternative symmetries like SU(5) or even [SU(3)]3, and (iii) the (B-L)-breaking scale being close to the unification scale [Formula: see text] GeV. The observed dramatic meeting of the three gauge couplings in the context of low-energy supersymmetry, at a scale [Formula: see text] GeV, providing strong evidence in favor of the ideas of both grand unification and supersymmetry, is discussed in Sec. 3. The implications of such a meeting in the context of string-unification are briefly mentioned. Weighing the possibility of a stringy origin of gauge coupling unification versus the familiar problem of doublet-triplet splitting in supersymmetric SO(10) (or SU(5)), I discuss the common advantages as well as relative merits and demerits of an effective SO(10) versus a string-derived [Formula: see text] symmetry in 4D. In Sec. 7, I discuss the hallmark prediction of grand unification, viz. proton decay, which is a generic feature of most models of grand unification. I present results of works carried out in collaboration with Babu and Wilczek and most recently with Babu and Tavartkiladze on expectations for decay modes and lifetimes for proton decay, including upper limits for such lifetimes, in the context of a well-motivated class of supersymmetric SO(10)-models. In view of such expectations, I stress the pressing need for having the next-generation large underground detectors — like DUNE and HyperKamiokande — coupled to long-baseline neutrino beams to search simultaneously with high sensitivity for (a) proton decay, (b) neutrino oscillations and (c) supernova neutrinos. It is remarked that the potential for major discoveries through these searches would be high. Some concluding remarks on the invaluable roles of neutrinos and especially of proton decay in probing physics at the highest energy scales are made in the last section. The remarkable success of a class of supersymmetric grand unification models (discussed here) in explaining a large set of distinct phenomena is summarized. Noticing such a success and yet its limitations in addressing some fundamental issues within its premises, such as an understanding of the origin of the three families, and most importantly, the realization of a well-understood unified quantum theory of gravity describing reality, some wishes are expressed on the possible emergence and the desirable role of a string-derived grand-unified bridge between string/M-theory in higher dimensions and the world of phenomena at low energies.

scholarly journals Fermion masses, neutrino oscillations, and proton decay in the light of superKamiokande

2000 ◽  
Vol 566 (1-2) ◽  
pp. 33-91 ◽  
Author(s):  
K.S. Babu ◽  
Jogesh C. Pati ◽  
Frank Wilczek
Keyword(s):  
Neutrino Oscillations ◽  
Proton Decay ◽  
Fermion Masses

scholarly journals THE PROBLEM OF NEUTRINO MASSES IN EXTENSIONS OF THE STANDARD MODEL

2001 ◽  
Vol 16 (32) ◽  
pp. 5101-5199 ◽  
Author(s):  
ISABELLA MASINA
Keyword(s):  
Proton Decay ◽  
Fine Tuning ◽  
Neutrino Masses ◽  
Flavor Symmetry ◽  
Mixing Angle ◽  
Grand Unified Theories ◽  
Triplet Splitting ◽  
Fermion Masses ◽  
The Standard Model ◽  
Neutrino Masses And Mixings

We review the problem of neutrino masses and mixings in the context of grand unified theories. After a brief summary of the present experimental status of neutrino physics, we describe how the see-saw mechanism can automatically account for the large atmospheric mixing angle. We provide two specific examples where this possibility is realized by means of a flavor symmetry. We then review in some detail the various severe problems which plague minimal GUT models (like the doublet–triplet splitting and proton-decay) and which force us to investigate the possibility of constructing more elaborate but realistic models. We then show an example of a quasirealistic SUSY SU(5) model which, by exploiting the crucial presence of an Abelian flavor symmetry, does not require any fine-tuning and predicts a satisfactory phenomenology with respect to coupling unification, fermion masses and mixings and bounds from proton decay.

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