424 research outputs found
Supersymmetry and Unification: Heavy Top Was the Key
I review the unification of gauge couplings of strong, weak and
electro-magnetic interactions. I start by recalling the history of the most
important prediction of low-energy supersymmetry: the correct value of the weak
mixing angle tied to a large top quark mass. I then turn to the discussion of
the present day situation of the minimal supersymmetric Grand Unified Theories
based on SU(5) and SO(10) groups, and I show why the minimal SU(5) is in accord
with experiment. For the sake of completeness I also summarize the problems and
possible solutions of the minimal ordinary SU(5). One version, based on the
minimal Georgi-Glashow model, augmented by the adjoint fermion, predicts a
light fermion triplet to lie below TeV or so. Its (lepton number violating)
decays offer a hope of probing neutrino (Majorana) masses and mixings at the
LHC.Comment: To be published in the proceedings of the Scientific and Human Legacy
of Julius Wess, Memorial Workshop held in Donji Milanovac, Serbia, August
201
Proton decay and grand unification
I review the theoretical and experimental status of proton decay theory and
experiment. Regarding theory, I focus mostly, but not only, on grand
unification. I discuss only the minimal, well established SU(5) and SO(10)
models, both ordinary and supersymmetric. I show how the minimal realistic
extensions of the original Georgi - Glashow model can lead to interesting LHC
physics, and I demonstrate that the minimal supersymmetric SU(5) theory is in
perfect accord with experiment. Since no universally accepted model has of yet
emerged, I discuss the effective operator analysis of proton decay and some
related predictions from a high scale underlying theory. A strong case is made
for the improvement of experimental limits, or better the search of, two body
neutron decay modes into charged kaons and charged leptons. Their discovery
would necessarily imply a low energy physics since they practically vanish in
any theory with a desert in energies between M_W and M_GUT.Comment: Based on the plenary talks at the SUSY09 and PASCOS09 conference
See-saw and grand unification
I review the profound connection between the see-saw mechanism for neutrino
masses and grand unification. This connection points naturally towards SO(10)
grand unified theory. The emphasis here is on the supersymmetric theory, but I
also discuss salient features of its split supersymmetry version and ordinary
non-supersymmetric SO(10). Particular attention is paid to the crucial issue of
the minimal such theory, i.e. the question of the Higgs sector needed to break
SO(10) down to the Minimal Supersymmetric Standard Model or the Standard Model.
Some essential features of the see-saw mechanism are clarified, in particular
its precise origin at the high scale.Comment: Talk given at SEESAW25: International Conference on the Seesaw
Mechanism and the Neutrino Mass, Paris, France, 10-11 Jun 200
A Truly Minimal Left-Right Symmetric Extension of the Standard Model
By invoking the existence of a general custodial O(2) symmetry, a minimal
Left-Right symmetric model based on the gauge group G=SU(2)L SU(2)R U(1)BL is
shown to require the existence of only two physical Higgs bosons. The lighter
Higgs is predicted to have a small mass which could be evaluated by standard
perturbation theory. The fermionic mass matrices are recovered by insertion of
ad hoc fermion-Higgs interactions. The model is shown to be undistinguishable
from the standard model at the currently reachable energies.Comment: 1 figure in a separate ps fil
Proton decay, supersymmetry breaking and its mediation
We study the breaking of supersymmetry and its transmission to the light
states in the context of the minimal SU(5) grand unified theory, with no
additional singlets. This simple theory can be taken as a prototype for a
program of breaking simultaneously grand unified symmetry and supersymmetry.
The main predictions are: (i) d=6 proton decay is completely negligible and d=5
is in accord with experiment, (ii) supersymmetry breaking is mainly mediated by
gravity.Comment: 18 page
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