[en] We study the generation of neutrino masses in the SU(3)_W electroweak unified theory in M₄xS₁/(Z₂xZ'₂) spacetime. By appropriate orbifolding, the bulk symmetry SU(3)_W is broken into SU(2)_LxU(1)_Y at one of the fixed points, where the quarks reside. The leptons form SU(3)_W triplets, localized at the other symmetric fixed point. The fermion masses arise from the bulk Higgs sector containing a triplet and an anti-sextet. We construct neutrino Majorana masses via 1-loop quantum corrections by adding a parity odd bulk triplet scalar. No right-handed neutrino is needed. The neutrino mass matrix is of the inverted hierarchy type. We show that the model can easily accommodate the bi-large mixing angle solution favored by the recent neutrino experiments without much fine tuning of parameters. The constraints from μ→3e transition and neutrinoless double β decays are discussed

[en] We study the leptonic CP violation by employing the complete set of dimension-six pure leptonic effective operators. Connection among the observable at different energy scales can be made by the running of the renormalization group equations. Explicitly, we study the charged lepton electric dipole moment, muon Michel decay, and the triple spin-momentum correlations at the Linear Collider. We found the electron electric dipole moment, which starts at 2-loop level, severely constrains the possibilities to detect the CP violating signatures in muon decay and at the linear colliders

[en] We consider the phenomenological consequences of a hidden Higgs sector extending the standard model (SM), in which the 'shadow Higgs' are uncharged under the SM gauge groups. We consider a simple U(1) model with one Higgs singlet. One mechanism which sheds light on the shadow sector is the mixing between the neutral gauge boson of the SM and the additional U(1) gauge group. The mixing happens through the usual mass mixing and also kinetic mixing, and is the only way the 'shadow Z' couples to the SM. We study in detail modifications that the presence of such shadow sector would bring to the electroweak precision tests, which in turn provide constraints on the kinetic-mixing parameter, s_ε, left free in our model. The shadow Z production rate at the CERN LHC and the International Linear Collider depends on s_ε. We find that the observable event rate at both facilities is possible for a reasonable range of s_ε allowed by electroweak precision tests

[en] We study a scale-invariant SU(2)xU(1)_YxU(1)_s model which has only dimensionless couplings. The shadow U(1)_s is hidden, and it interacts with the standard model (SM) solely through mixing in the scalar sector and kinetic mixing of the U(1) gauge bosons. The gauge symmetries are broken radiatively by the Coleman-Weinberg mechanism. Lifting of the flat direction in the scalar potential gives rise to a light scalar, the scalon, or the shadow Higgs, and a heavier scalar which we identify as the SM Higgs boson. The phenomenology of this model is discussed. In particular, the constraints on the shadow Higgs in different mass ranges, and the possibility of discovering a shadow Higgs with a mass a few tens of GeV in precision t-quark studies at the LHC, are investigated

[en] We continue our previous study on what are the allowed forms of quark mass matrices in the Randall-Sundrum framework that can reproduce the experimentally observed quark mass spectrum and the pattern of Cabibbo-Kobayashi-Maskawa mixing. We study the constraints the ΔF=2 processes in the neutral meson sector placed on the admissible forms found there, and we found only the asymmetrical type of quark mass matrices arising from anarchical Yukawa structures remain viable at the few TeV scale reachable at the LHC. We study also the decay of the first Kaluza-Klein (KK) excitation of the gluon. We give the decay branching ratios of the first KK gluon into quark pairs, and we point out that measurements of the decay width and just one of the quark spins in the dominant tt decays can be used to extract the effective coupling of the first KK gluon to top quarks for both chiralities. This provides a further probe into the flavor structure of the Randall-Sundrum framework.

[en] We study an important contribution to the electric dipole moment (EDM) of the electron (or quarks) at the two-loop level due to the W-EDM in the recently proposed scenario of split supersymmetry. This contribution is independent of the Higgs mass, and it can enhance the previous estimation of the electron (neutron) EDM by 20-50% (40-90%). Our formula is new in its analytical form

[en] Models involving large extra spatial dimension(s) have interesting predictions on lepton flavor violating processes. We consider some five-dimensional (5D) models which are related to neutrino mass generation or address the fermion masses hierarchy problem. We study the signatures in low energy experiments that can discriminate the different models. The focus is on muon-electron conversion in nuclei μ→eγ and μ→3e processes and their τ counterparts. Their links with the active neutrino mass matrix are investigated. We show that in the models we discussed the branching ratio of μ→eγ like rare process is much smaller than the ones of μ→3e like processes. This is in sharp contrast to most of the traditional wisdom based on four-dimensional (4D) gauge models. Moreover, some rare tau decays are more promising than the rare muon decays

[en] We implement Dirac neutrinos in the minimal custodial Randall-Sundrum setting via the Krauss-Wilczek mechanism. We demonstrate by giving explicit lepton mass matrices that with neutrinos in the normal hierarchy, lepton mass and mixing patterns can be naturally reproduced at the scale set by the constraints from electroweak precision measurements, and at the same time without violating bounds set by lepton flavor violations. Our scenario generically predicts a nonzero neutrino mixing angle θ₁₃, as well as the existence of sub-TeV right-handed Kaluza-Klein neutrinos, which partner the right-handed standard model charged leptons. These relatively light KK neutrinos may be searched for at the LHC.

[en] We study in an effective operator approach how the effects of new physics from various scenarios that contain an extra Z^' neutral gauge boson or doubly charged scalars, can affect and thus be tested by the precision polarized Moeller scattering experiments. We give Wilson coefficients for various classes of generic models, and we deduce constraints on the parameter space of the relevant coupling constants or mixing angles from the results of the SLAC E158 experiment where applicable. We give also constraints projected from the upcoming 1 ppb JLAB experiment. In the scenario where the extra Z^' is light (M_Z^'<< M_W), we obtain further constraints on the parameter space using the BNL g-2 result where it is useful. We find that the BNL deviation from the standard model cannot be attributed to a light extra Z^' neutral gauge boson.

[en] A commonly accepted mechanism of generating baryon asymmetry in the minimal supersymmetric standard model (MSSM) depends on the CP violating relative phase between the gaugino mass and the Higgsino μ term. The direct constraint on this phase comes from the limit of electric dipole moments (EDM's) of various light fermions. To avoid such a constraint, a scheme which assumes that the first two generation sfermions are very heavy is usually evoked to suppress the one-loop EDM contributions. We point out that under such a scheme the most severe constraint may come from a new contribution to the electric dipole moment of the electron, the neutron, or atoms via the chargino sector at the two-loop level. As a result, the allowed parameter space for baryogenesis in the MSSM is severely constrained, independent of the masses of the first two generation sfermions