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Register a new userProton Decay in Supersymmetric $SU(4)_c times SU(2)_L times SU(2)_R$
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We discuss proton decay in a recently proposed model of supersymmetric hybrid inflation based on the gauge symmetry $SU(4)_c times SU(2)_L times SU(2)_R$. A $U(1), R$ symmetry plays an essential role in realizing inflation as well as in eliminating some undesirable baryon number violating operators. Proton decay is primarily mediated by a variety of color triplets from chiral superfields, and it lies in the observable range for a range of intermediate scale masses for the triplets. The decay modes include $p rightarrow e^{+}(mu^+) + pi^0$, $p rightarrow bar{ u} + pi^{+}$, $p rightarrow K^0 + e^+(mu^{+})$, and $p rightarrow K^+ + bar{ u}$, with a lifetime estimate of order $10^{34}-10^{36}$ yrs and accessible at Hyper-Kamiokande and future upgrades. The unification at the Grand Unified Theory (GUT) scale $M_{rm GUT}$ ($sim 10^{16}$ GeV) of the Minimal Supersymmetric Standard Model (MSSM) gauge couplings is briefly discussed.
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We explore the sparticle mass spectra including LSP dark matter within the framework of supersymmetric $SU(4)_c times SU(2)_L times SU(2)_R$ (422) models, taking into account the constraints from extensive LHC and cold dark matter searches. The soft supersymmetry-breaking parameters at $M_{GUT}$ can be non-universal, but consistent with the 422 symmetry. We identify a variety of coannihilation scenarios compatible with LSP dark matter, and study the implications for future supersymmetry searches and the ongoing muon g-2 experiment.
Motivated by the ongoing searches for new physics at the LHC, we explore the low energy consequences of a D-brane inspired $ SU(4)_Ctimes SU(2)_L times SU(2)_R$ (4-2-2) model. The Higgs sector consists of an $SU(4)$ adjoint, a pair $H+bar H$ in $(4,1,2)+(bar 4,1,2)$, and a bidoublet field in $h(1,2,2)$. With the $SU(4)$ adjoint the symmetry breaks to a left-right symmetric $SU(3)_Ctimes U(1)_{B-L} times SU(2)_L times SU(2)_R$ model. A missing partner mechanism protects the $SU(2)_R$ Higgs doublets in $H,bar H$, which subsequently break the symmetry to the Standard Model at a few TeV scale. An inverse seesaw mechanism generates masses for the observed neutrinos and also yields a sterile neutrino which can play the r^ole of dark matter if its mass lies in the keV range. Other phenomenological implications including proton decay are briefly discussed.
In the $SU(6) times SU(2)_R$ string-inspired model, we evolve the couplings and the masses down from the string scale $M_S$ using the renormalization group equations and minimize the effective potential. This model has the flavor symmetry including the binary dihedral group $tilde{D}_4$. We show that the scalar mass squared of the gauge non-singlet matter field possibly goes negative slightly below the string scale. As a consequence, the precocious radiative breaking of the gauge symmetry down to the standard model gauge group can occur. In the present model, the large Yukawa coupling which plays an important role in the symmetry breaking is identical with the colored Higgs coupling related to the longevity of the proton.
The lepton masses and mixings are studied on the basis of string inspired $SU(6)times SU(2)_R$ model with global flavor symmetries. Provided that sizable mixings between lepton doublets $L$ and Higgsino-like fields $H_d$ with even R-parity occur and that seesaw mechanism is at work in the neutrino sector, the model can yield a large mixing angle solution with $tan theta_{12}, tan theta_{23} = O(sqrt{l})$ $({l}= 0.22)$, which is consistent with the recent experimental data on atmospheric and solar neutrinos. In the solution Dirac mass hierarchies in the neutrino sector cancel out with the heavy Majorana sector in large part due to seesaw mechanism. Hierarchical pattern of charged lepton masses can be also explained.
We introduce the flavor symmetry ${bf Z}_M times {bf Z}_N times D_4$ into the $SU(6) times SU(2)_R$ string-inspired model. The cyclic group ${bf Z}_M$ and the dihedral group $D_4$ are R symmetries, while ${bf Z}_N$ is a non-R symmetry. By imposing the anomaly-free conditions on the model, we obtain a viable solution under many phenomenological constraints coming from the particle spectra. For neutrino sector, we find a LMA-MSW solution but not SMA-MSW ones. The solution includes phenomenologically acceptable results concerning fermion masses and mixings and also concerning hierarchical energy scales including the GUT scale, the $mu$ scale and the Majorana mass scale of R-handed neutrinos.
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