78 research outputs found
The Essential Role of String-Derived Symmetries in Ensuring Proton-Stability and Light Neutrino Masses
The paper addresses the problem of suppressing naturally the unsafe d=4 as
well as the color-triplet mediated and/or gravity-linked d=5 proton-decay
operators, which generically arise in SUSY-unification. It also attempts to
give light masses to the neutrinos, of the type suggested by current
experiments. It is noted that neither the symmetries in , nor those in
, suffice for the purpose -- especially in the matter of suppressing
naturally the d=5 proton-decay operators. By contrast, it is shown that a
certain {\it string-derived symmetry}, which cannot arise within conventional
grand unification, but which does arise within a class of three-generation
string-solutions, suffices, in conjuction with , to safeguard
proton-stability from all potential dangers, including those which may arise
through higher dimensional operators and the color-triplets in the infinite
tower of states. At the same time, the symmetry in question permits neutrinos
to acquire appropriate masses. This shows that {\it string theory plays an
essential role in ensuring natural consistency of SUSY-unification with two
low-energy observations -- proton-stability and light masses for the
neutrinos}. The correlation between the masses of the extra -boson (or
bosons), which arise in these models, and proton-decay rate is noted.Comment: 20 pages, plain LaTeX. Footnote 26 expanded to include implication of
neutrino-higgsino mixing, and two new footnotes adde
The Role of Gravity in Determining Physics at High as Well as Low Energies
It is noted that in the context of a supersymmetric preonic approach to
unification, gravity, though weak, can play an essential role in determining
some crucial aspects of low-energy physics. These include: (i) SUSY-breaking,
(ii) electroweak symmetry-breaking, and (iii) generation of masses of quarks
and leptons, all of which would vanish if we turn off gravity. Such a role of
gravity has its roots in the Witten index theorem which would forbid
SUSY-breaking, within the class of theories under consideration, in the absence
of gravity.Comment: 14 pages, 2 figures, Plain Te
Discovery of Proton Decay: A Must for Theory, a Challenge for Experiment
It is noted that, but for one missing piece -- proton decay -- the evidence
in support of grand unification is now strong. It includes: (i) the observed
family-structure, (ii) the meeting of the gauge couplings, (iii)
neutrino-oscillations, (iv) the intricate pattern of the masses and mixings of
all fermions, including the neutrinos, and (v) the need for as a
generator, to implement baryogenesis. Taken together, these not only favor
grand unification but in fact select out a particular route to such
unification, based on the ideas of supersymmetry, SU(4)-color and left-right
symmetry. Thus they point to the relevance of an effective string-unified
G(224) or SO(10)-symmetry.
A concrete proposal is presented, within a predictive
SO(10)/G(224)-framework, that successfully describes the masses and mixings of
all fermions, including the neutrinos - with eight predictions, all in
agreement with observation. Within this framework, a systematic study of proton
decay is carried out, which pays special attention to its dependence on the
fermion masses, including the superheavy Majorana masses of the right-handed
neutrinos. The study shows that a conservative upper limit on the proton
lifetime is about (1/2 - 1) yrs, with
being the dominant decay mode, and as a distinctive feature,
being prominent. This in turn strongly suggests that an improvement in the
current sensitivity by a factor of five to ten (compared to SuperK) ought to
reveal proton decay. Otherwise some promising and remarkably successful ideas
on unification would suffer a major setback.Comment: LaTex file 29 pages, no figures. Minor correction
With Grand Unification Signals in, Can Proton Decay be Far Behind?
It is noted that one is now in possession of a set of facts, which may be
viewed as the matching pieces of a puzzle ; in that all of them can be resolved
by just one idea - that is grand unification. These include : (i) the observed
family-structure, (ii) quantization of electric charge, (iii) meeting of the
three gauge couplings, (iv) neutrino oscillations; in particular the mass of
suggested by SuperK), (v) the intricate pattern of the masses and
mixings of the fermions, including the smallness of and the largeness
of , and (vi) the need for - to
implement baryogenesis (via leptogenesis). All these pieces fit beautifully
together within a single puzzle board framed by supersymmetric unification,
based on SO(10) or a string-unified G(224)-symmetry. The one and the most
notable piece of the puzzle still missing, however, is proton decay. A concrete
proposal is presented, within a predictive SO(10)/G(224)-framework, that
successfully describes the masses and mixings of all fermions, including the
neutrinos - with eight predictions, all in agreement with observation. An
updated study of proton decay is carried out within this framework, which shows
that a conservative upper limit on its lifetime is about (1/2-1)\times 10^34
yrs
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