Orbifold Compactification and Related Phenomenology
In this lecture, starting with GUT we go through the field theoretic and stringy orbifold compactification of extra dimensions toward their application to low energy particle physics.
hep-ph↗
arXiv subjects
Kyuwan Hwang
Publications and source records attributed to Kyuwan Hwang.
Higgsino mass matrix ansatz for MSSM
An ansatz, Det. $M_{\tilde H}=0,$ for the Higgsino mass matrix in string orbifold trinification is suggested toward the minimal supersymmetric standard model(MSSM). Small instanton solutions effective around the GUT scale can fulfil this condition. An argument that the couplings contain a moduli field is given for a dynamical realization of this Higgsino mass matrix ansatz.
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Dynkin diagram strategy for orbifolding with Wilson lines
A simple method for breaking gauge groups by orbifolding is presented. We extend the method of Kac and Peterson to include Wilson lines. The complete classification of the gauge group breaking, e.g. from heterotic string, is now possible. From this Dynkin diagram technique, one can easily visualize the origin and the symmetry pattern of the surviving gauge group.
hep-th↗
Orbifolded SU(7) and unification of families
A 5D SU(7) family unification model with two spinor representations of SO(14) is presented. The fifth dimension is compactified on $S^1/Z_2\times Z_2'$. The orbifolding is used to obtain 4D SO(10) chiral fermions. The 4D grand unification group is the flipped $SU(5)\times U(1)$. The doublet-triplet splitting through the missing partner mechanism is achieved. Also, fermion mass matrices are considered.
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Sneutrino-Antisneutrino Mixing and Neutrino Mass in Anomaly--mediated Supersymmetry Breaking Scenario
In supersymmetric models with nonzero Majorana neutrino mass, the sneutrino and antisneutrino mix, which may lead to same sign dilepton signals in future collider experiments. We point out that the anomaly-mediated supersymmetry breaking scenario has a good potential to provide an observable rate of such signals for the neutrino masses suggested by the atmospheric and solar neutrino oscillations. The sneutrino mixing rate is naturally enhanced by m_{3/2}/m_{\tildeν}={\cal O}(4π/α) while the sneutrino decay rate is small enough on a sizable portion of the parameter space. We point out also that the sneutrino-antisneutrino mixing can provide much stronger information on some combinations of the neutrino masses and mixing angles than neutrino experiments.
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Bi-maximal neutrino mixing and small U_{e3} from Abelian flavor symmetry
Atmospheric neutrino data strongly suggests a near-maximal ν_μ-ν_τ mixing and also solar neutrino data can be nicely explained by another near-maximal ν_e-ν_μ or ν_e-ν_τ mixing. We examine the possibility that this bi-maximal mixing of atmospheric and solar neutrinos arises naturally, while keeping U_{e3} and Δm^2_{sol}/Δm^2_{atm} small enough, as a consequence of Abelian flavor symmetry. Two simple scenarios of Abelian flavor symmetry within supersymmetric framework are considered to obtain the desired form of the neutrino mass matrix and the charged lepton mass matrix parameterized by the Cabibbo angle λ\approx 0.2. Future experiments at a neutrino factory measuring the size of U_{e3} and the sign of Δm^2_{32} could discriminate those scenarios as they predict distinctive values of U_{e3} in connection with Δm^2_{sol}/Δm^2_{atm} and also with the order of the neutrino mass eigenvalues.
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Probing the messenger of supersymmetry breaking by the muon anomalous magnetic moment
Motivated by the recently measured muon's anomalous magnetic moment $a_μ$, we examine the supersymmetry contribution to $a_μ$ in various mediation models of supersymmetry breaking which lead to predictive flavor conserving soft parameters at high energy scale. The studied models include dilaton/modulus-mediated models in heterotic string/$M$ theory, gauge-mediated model, no-scale or gaugino-mediated model, and also the minimal and deflected anomaly-mediated models. For each model, the range of $a^{SUSY}_μ$ allowed by other experimental constraints, e.g. b --> sγand the collider bounds on superparticle masses, is obtained together with the corresponding parameter region of the model. Gauge-mediated models with low messenger scale can give any $a^{SUSY}_μ$ within the $2σ$ bound. In many other models, b --> sγfavors $a^{SUSY}_μ$ smaller than either the $-1σ$ value ($26\times 10^{-10}$) or the central value ($42\times 10^{-10}$).
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Axino as a sterile neutrino and R parity violation
We point out that axino can be a natural candidate for sterile neutrino which would accommodate the LSND data with atmospheric and solar neutrino oscillations. It is shown that the so called 3+1 scheme can be easily realized when supersymmetry breaking is mediated by gauge interactions and also R-parity is properly broken. Among the currently possible solutions to the solar neutrino problem, only the large angle MSW oscillation is allowed in this scheme. The weak scale value of the Higgs $μ$ parameter and the required size of R-parity violation can be understood by means of spontaneously broken Peccei-Quinn symmetry.
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CP Asymmetries in Radiative B Decays with R-parity Violation
We analyze the effect of R-parity violation in the minimal supersymmetric standard model on the CP asymmetries in $b\to s γ$ decay. The direct and mixing-induced CP asymmetries arising from the lepton number violating couplings are strongly constrained by the current experimental limits on the corresponding couplings. Allowing a heavy neutrino ($m_{ν_τ}\sim10$ keV) and a moderate mass splitting of sfermions, the direct CP asymmetry around 15 % and the nearly maximal mixing-induced CP asymmetry ($\sim 100 %$) can be realized, depending on the R-parity conserving contributions to the radiative $b$ decay. With the baryon number violating couplings, only the mixing-induced CP asymmetry arises and it can be maximal provided there is a the similar sfermion mass splitting.
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Lepton Flavor Violation and Bilinear R-parity Violation
We examine some flavor changing processes such as rare leptonic decays of the long-lived neutral kaon, muon-electron conversion in nuclei and radiative muon decay which are induced by the combined effects of bilinear and trilinear R-parity violations. These processes are used to put strong constraints on certain products of the bilinear and trilinear couplings. We also discuss the constraints on R-parity violation from neutrino masses and compare them with the constraints from flavor changing decay processes. Large range of parameter space satisfying the constraints from neutrino masses can be excluded by the flavor changing processes considered in this paper, and also vice versa.
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Fermion Electric Dipole Moments in Supersymmetric Models with R-parity Violation
We analyze the electron and neutron electric dipole moments induced by R-parity violating interactions in supersymmetric models. It is pointed out that dominant contributions can come from one-loop diagrams involving both the bilinear and trilinear R-parity odd couplings, leading to somewhat severe constraints on the products of those couplings.
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Cosmological Gravitino Production in Gauge Mediated Supersymmetry Breaking Models
We study the cosmological gravitino production in gauge mediated supersymmetry breaking models, while properly taking into account the existence of the messenger mass scale. It is found that for sizable parameter range of the model the messenger sector contribution leads to more stringent upper bound on the reheat temperature obtained from the condition that the universe should not be overclosed by relic gravitinos. However it turns out that in the limit of relatively low messenger scale and large gravitino mass, the relic gravitino mass density can be smaller than the critical density independently of the reheat temperature, suggesting the possibility in this limit to have a high reheat temperature without the dilution of gravitinos at late time.
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Atmospheric and Solar Neutrino Masses from Horizontal U(1) Symmetry
We study the neutrino mass matrix in supersymmetric models in which the quark and charged lepton mass hierarchies and also the suppression of baryon or lepton number violating couplings are all explained by horizontal $U(1)_X$ symmetry. It is found that the neutrino masses and mixing angles suggested by recent atmospheric and solar neutrino experiments arise naturally in this framework which fits in best with gauge-mediated supersymmetry breaking with large $\tanβ$. This framework highly favors the small angle MSW oscillation of solar neutrinos, and determine the order of magnitudes of all the neutrino mixing angles and mass hierarchies.
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Constraints on R parity and B violating couplings in gauge-mediated supersymmetry breaking models
We consider the proton decay involving a light gravitino or axino in gauge-mediated supersymmetry breaking models to derive constraints on the $R$ parity and baryon number violating Yukawa couplings. Bounds on all nine coupling constants are obtained by considering the decay amplitudes at one-loop order.
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