In this paper we study the ZЈ contribution to gϪ2 of the muon anomalous magnetic dipole moment in gauged U(1) L -L models. Here L i are the lepton numbers. We find that there are three classes of models which can produce a large value of gϪ2 to account for the possible discrepancy between the experimental data and the standard model prediction. The three classes are as follows: ͑a͒ Models with an exact U(1) L -L . In these models, ZЈ is massless. The new gauge interaction coupling ea/cos W is constrained to be 0.8ϫ10 Ϫ3 Ͻ͉a͉ Ͻ2.24ϫ10 Ϫ3 . ͑b͒ Models with broken U(1) L -L and the breaking scale is not related to electroweak symmetry breaking scale. The ZЈ gauge boson is massive. The allowed range of the coupling and the ZЈ mass are constrained, but ZЈ mass can be large. ͑c͒ The U(1) L -L is broken and the breaking scale is related to the electroweak scale. In this case the ZЈ mass is constrained to be ϳ1.2 GeV. We find that there are interesting experimental signatures in ϩ Ϫ → ϩ Ϫ , ϩ Ϫ in these models.

We revisit the Higgs portal vector dark matter model including a hidden sector Higgs field that generates the mass of the vector dark matter. The model becomes renormalizable and has two scalar bosons, the mixtures of the standard model (SM) Higgs and the hidden sector Higgs bosons. The strong bound from direct detection such as XENON100 is evaded due to the cancellation mechanism between the contributions from two scalar bosons. As a result, the model becomes still viable in large range of dark matter mass, contrary to some claims in the literature. The Higgs properties are also affected, the signal strengths for the Higgs boson search being universally suppressed relative to the SM value, which could be tested at the LHC in the future.

The effects of supersymmetric particles on flavor changing neutral current and lepton flavor violating processes are studied in supersymmetric SU͑5͒ grand unified theory with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of radiative B decay can be as large as 25% when the →␥ branching ratio becomes close to the present experimental upper bound. We also show that the B s -B s mixing can be significantly different from the presently allowed range in the standard model.

We consider a simple extension of the standard model with a singlet fermionic dark matter. Its thermal relic density can be easily accommodated by a real singlet scalar messenger that mixes with the standard model Higgs boson. The model can change significantly the Higgs signals at the LHC via sizable invisible decays of two Higgs-like scalar bosons. After imposing the constraints from the electroweak precision tests, colliders and dark matter search experiments, one concludes that two or one or none of the two Higgs bosons, depending on the mass relations among two scalar bosons and the dark matter fermion and their couplings. In particular, if a standard model Higgs-like scalar boson is discovered around 120-125 GeV region at the LHC, it would be almost impossible to find the second Higgs-like boson since it is mostly a singlet scalar, whether it is heavier or lighter. This model can be further tested by direct dark matter search experiments.

Abstract:We consider the issue of vacuum stability and triviality bound of the singlet extension of the Standard Model (SM) with a singlet fermion dark matter (DM). In this model, the singlet scalar plays the role of a messenger between the SM sector and the dark matter sector. This model has two Higgs-like scalar bosons, and is consistent with all the data on electroweak precision tests, thermal relic density of DM and its direct detection constraints. We show that this model is stable without hitting Landau pole up to Planck scale for 125 GeV Higgs boson. We also perform a comprehensive study of vacuum structure, and point out that a region where electroweak vacuum is the global minimum is highly limited. In this model, both Higgs-like scalar bosons have reduced couplings to the SM weak gauge bosons and the SM fermions, because of the mixing between the SM Higgs boson and the singlet scalar. There is also a possibility of their invisible decay(s) into a pair of DM's. Therefore this model would be disfavored if the future data on the (σ · B) V V or (σ · B) ff with V = γ, W, Z and f = b, τ turn out larger than the SM predictions.