The anomalous chromomagnetic moment of the top quark arises from one loop corrections to the vertex ttg. We give explicit formulas for this anomalous coupling in the framework of the standard model, the two Higgs doublet model and the minimal supersymmetric standard model. We compare the results for the anomalous coupling with the bound Ϫ0.03р⌬р0.01 emerging from the analysis of the b→s␥ process with an on-shell bremsstrahlung gluon. This enables us to study the allowed region of parameters of the models under consideration.

An interesting extension of the standard model is based on the electroweak gauge group SU3 L U1. It requires three generations to cancel anomalies, treats the third generation differently than the first two, and has a rich phenomenology. There are several models, distinguished by the embedding of the charge operator into the SU3 L group and by the choice of fermion representations. In this brief report, we consider flavor-changing neutral currents in these models, concentrating on the P ÿ P mass difference, where P K; D; B; B s , as well as B ! Kl l ÿ , B ! ÿ , and B s ! ÿ decays. Although the P ÿ P mass difference has been considered previously in some models, the rare B decays are new. We find that the strongest bounds come from the B ÿ B and B s ÿ B s mass difference.

We present a new supersymmetric version of the SU (3) ⊗ U (1) gauge model using a more economic content of particles. The model has a smaller set of free parameters than other possibilities considered before. The MSSM can be seen as an effective theory of this larger symmetry. We find that the upper bound of the ligthest CPeven Higgs boson can be moved up to 140 GeV.

We constrain some lepton flavor violating vertices in the context of the two Higgs doublet model type III, assuming that the lightest scalar Higgs mass m h 0 is about 115 GeV. Specifically, based on the g − 2 muon factor and the decay width of µ → eγ, the following quite general bounds are obtained: 7.62 × 10 2.77 × 10 −14 . Additionally, based on the processes τ → µγ, and τ → µµµ, bounds on ξττ and ξµµ are also gotten, such constraints on these parameters still give enough room for either a strong suppression or strong enhancement on the coupling of any Higgs boson to a pair of tau leptons or a pair of muons. Furthermore, upper limits on the decay widths of the leptonic decays τ → eγ, and τ → eee are calculated, finding them to stay far from the reach of near future experiments.

The branching ratios of the lightest CP-even Higgs boson h 0 are calculated in the framework of the general two higgs doublet model. Different scenarios are presented taking into account constraints on the flavor changing neutral currents factors obtained in previous works. Plausible scenarios where appear flavor changing processes at tree level like b s and t c are analyzed for relevant parameters. The loopinduced Higgs couplings to photon pairs can be tested with a photon collider. The number of events of h 0 as a resonance in photon colliders are calculated taking into account its corresponding background signal at TESLA, CLIC, and NLC.