Search

Processes $\tau\rightarrow l\gamma$, $\tau\rightarrow lll$ with $l= e,\mu$ and $\mu(\tau) \to e (\mu) \gamma$ are evaluated in the framework of a model based on the extended symmetry gauge $SU(3)_c \otimes SU(3)_L \otimes U(1)_Y$ with a leptonic sector consistent of five triplets. Lepton flavor violating processes are allowed at tree level in this model through the new $Z'$ gauge boson. We obtained bounds for the mixing angles in the leptonic sector of the model, considering the experimental measurements of the processes from the BELLE and the BABAR collaborations., Comment: arXiv admin note: substantial text overlap with arXiv:1212.3586

We obtain electric charge quantization in the context of models based on the gauge symmetry group SU(3) X SU(4) X U(1). The gauge models studied include three families to cancel out anomalies and a set of scalar fields to break spontaneously the symmetry. To show the electric charge quantization, we use clasical symmetry conditions and quantum quiral anomaly conditions., Comment: 9 pages

Models based on the extended symmetry gauge $SU(3)_c \otimes SU(3)_L \otimes U(1)_Y$ can be build up with a leptonic sector consistent of five triplets in different $SU(3)_L$ representations where additional heavy fermions are included. Some of these models present flavor changing neutral currents in the leptonic sector which are mediated through the $Z'$ boson. One of these models is studied using the measurements of lepton flavor violation processes such as $\tau\rightarrow lll$ with $l= e,\mu$ and $\mu(\tau) \to e (\mu) \gamma$., Comment: Proceedings, The XIth International Conference on Heavy Quarks and Leptons, 11-15 June, 2012. Prague,The Czech Republic

We consider a three Higgs doublet model with an $S_3$ symmetry in which beside the SM-like doublet there are two fermiophobic doublets. Due to the new charged scalars there is an enhancement in the two-photon decay while the other channels have the same decay widths that the SM neutral Higgs. The fermiophobic scalars are mass degenerated unless soft terms breaking the $S_3$ symmetry are added., Comment: typos were corrected, the figures have been modified and the conclusions were increased. Still contains 15 pages, 2 figures

The most commonly used parameterizations of the Yukawa couplings in the two Higgs doublet model are revisited. Their similitudes and differences are emphasized and relations between the different notations used in the literature are derived. Using these relations, bounds on the space of parameters of the charged Higgs sector of the two Higgs doublet model are obtained. These constraints are obtained from flavor observables like the measurement of B -> Xs \gamma and the recent measurement of Bs -> \mu+ \mu- from LHCb. The ratio R_{H+}=B(H+ -> \tau^+ \nu_\tau)/B(H+ -> t b) is evaluated for the two Higgs doublet model type-III and type-II, and their differences are quantified., Comment: 14 pages, 5 figures, 2 tables

There are different models based on the gauge symmetry $SU(3)_C \otimes SU(3)_L \otimes U(1)_X$ (331) some of them includes exotic particles and others are constructed without any exotic charges assigned to the fermionic spectrum. Each model build up on 331 symmetry has its own interesting properties according to the representations of the gauge group used for the fermionic spectrum; that is the main reason to explore and identify the possible sources of flavor changing neutral currents and lepton flavor violation at tree level., Comment: 14 pages, Prepared for the special issue "Non-Abelian Gauge Symmetries beyond the Standard Model" of Advances in High Energy Physics

By using the Cheng, Sher and Yuan's anzats, we study the light Higgs Boson production associated with $b$ quark production at TEVATRON using the 2HDM type III. We compare the simulations with experimental results coming from TEVATRON, finding valid ranges for the $bb$ coupling. By using these results, we calculate the cross section for the process $pp \to b\bar bh(b\bar b)$ for the LHC collider., Comment: $ pages, 4 figures, to appear Brazilian Journal of Physics

We study charged Higgs production in the process $\gamma\gamma\to A^0\to W^- H^+$. The processes $\gamma\gamma\to A^0$ are loop mediated in a 2HDM. This is due to the fact that photons only couple directly to charged particles and the Higgs only couples to particles with mass acquired via Higgs mechanism. Although in MSSM the contribution from the process $\gamma\gamma\to A^0$ is too small, it has been found that in a more general 2HDM it could be enhanced. On the other hand, the boson $A^0$ can decay in $W^- H^+$ at tree level and the charged Higgs can decay in fermions. So, the whole process under study is $\gamma\gamma\to A^0\to (W^-\to l\nu) (H^+\to f_if_j)$ in 2HDM-III. Evidence about charged Higgs existence could demonstrate that structure of the Higgs sector has several multiplets., Comment: 5 pages, 4 figures, to appear Brazilian Journal of Physics

The D0 experiment has reported a direct search for a charged Higgs boson produced by $q \bar q$ annihilation and decaying to $t \bar b$ final state, in the $180 \leq M_{H^+} \leq 300$ GeV mass range. The analysis has lead to upper limits on the production cross section in the framework of the two Higgs doublet model types I, II and III. We compare the predictions of two different scenarios in the framework of the two Higgs doublet type III to the cross section limits reported by D0 collaboration, and we obtain constraints on the charged Higgs mass, for the case when the charged Higgs mass is bigger than the top quark mass. Also, searches for the charged Higgs boson with a mass smaller than top quark mass are considered, we discuss the possible limits on the charged Higgs boson mass obtained from measurements of the ratio $R_\sigma=\sigma_{t \bar t}^{l+jets}/\sigma_{t \bar t}^{dileptons}$ within the two Higgs doublet model type III., Comment: 11 pages, 4 figures, version to be published

The oscillation periods bounded by a simple pendulum and an oscillating rigid rod are illustrated using a multiple pendulum. Oscillation periods between these two limits are obtained. A theoretical approach using the Lagrangian formalism and the set up of three simple experiments are presented in order to probe our approach., Comment: 10 pages, 7 figures, IOP style

The quark mass matrices ansatze proposed by Fritzsch, Du-Xing and Fukuyama-Nishiura in the framework of the general two Higgs doublet model are studied. The corresponding Yukawa matrices in the flavor basis in the different cases considered are discussed. The corresponding Cabbibo-Kobayashi-Maskawa matrix elements are computed in all cases and compared with their experimental values. The complex phases of the ansatze are taken into account and the CP violating phase $\delta$ is computed. Finally, in order to observe the influence of the different kind of textures of Yukawa coupling matrices considered, some phenomenology of two body decays of the top quark, the lightest Higgs boson and the charged Higgs boson is discussed., Comment: 14 pages, 1 figure. Added references, corrected typos. Errors corrected. References added

The flavor changing neutral top quark decay t -> c X is computed, where X is a neutral standard model particle, in a extended model with a single extra dimension. The cases for the photon, X= \gamma$, and a Standard Model Higgs boson, X = H, are analyzed in detail in a non-linear$R_\xi gauge. We find that the branching ratios can be enhanced by the dynamics originated in the extra dimension. In the limit where 1/R >> ->, we have found Br(t -> c \gamma) \simeq 10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH) \simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero when 1/R -> \infty., Comment: Accepted to be published in the Europ. Phys. Jour. C; 16 pages, 2 figures

We consider the Two Higgs Doublet Model (2HDM) of type III which leads to Flavour Changing Neutral Currents (FCNC) at tree level. In the framework of this model we calculate the NLO contribution for b->s \gamma and the branchings for the meson decays B^+ -> l^+ \nu. We examine the limits on the new parameters \lambda_{bb} and M_{H^\pm}. We take into account the relationship between \lambda_{tt} and \lambda_{bb} coming from the validness of perturbation theory.

The branching ratios of the lightest CP-even Higgs boson $h^0$, in the framework of the General Two Higgs Doublet Model are calculated. Different scenarios are presented taking into account constraints obtained in previous works on the flavor changing neutral currents factors. Plausible scenarios with flavour changing processes at tree level like $b \bar s$ and $t \bar c$ are analyzed for relevant region of parameters. The loop-induced 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 in TESLA, CLIC and NLC., Comment: 1. Universidad Nacional de Colombia, Bogota, Colombia. (2) Universidad de Valencia, Valencia, Spain. 21 pages, 5 figures, RevTeX

An interesting extension of the Standard Model is based on the electroweak gauge group SU(3)_L x U(1). 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 SU(3)_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-Pbar mass difference, where P=(K, D, B, B_s), as well as B --> K l^+ l^-, B --> mu^+ mu^- and B_s --> mu^+ mu^- decays. Although the P-Pbar 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-Bbar and Bs-Bs-bar mass differences., Comment: 14 pages, no figures

We calculate the two body Higgs boson decays in the framework of the littlest Higgs model. The decay $H \to \gamma Z$ is computed at one loop level and, using previous results, we evaluate the branching fractions in the framework of the littlest Higgs model. A wide range of the space parameter of the model is considered and possible deviations from the standard model are explored., Comment: 13 pages, 5 figures

A supersymmetric version of the $SU(3)_L \otimes U(1)_X$ gauge model is presented. The model is embedded in a $SU(6)_L \otimes U(1)_X$ gauge group and it has been built up completely quiral anomaly free and without any exotic charges in the fermionic content. The Minimal Supersymmetric Standard Model can be seen as an effective theory of this larger symmetry. We analyze how the spectrum of the new model can shift the upper bound on the CP-even Higgs boson and we find that it can be moved up to 143 GeV., Comment: Universidad Nacional de Colombia, 14 pages, 2 figures, RevTeX. Typos corrected. Version be published in Physical Review D

Anomalous moments of the top quark arises from one loop corrections to the vertices $\bar t t g$ and $\bar t t \gamma$. We study these anomalous couplings in different frameworks: effective theories, Standard Model and 2HDM. We use available experimental results in order to get bounds on these anomalous couplings., Comment: 8 pages, 2 figures, talk presented by R. Martinez at the X Mexican School of Particles and Fields, Playa del Carmen, Mexico, 2002

We consider the Two Higgs Doublet Model (2HDM) of type III which leads to Flavour Changing Neutral Currents (FCNC) at tree level. In the framework of this model we can use an appropriate form of the Yukawa Lagrangian that makes the type II model limit of the general type III couplings apparent. This way is useful in order to compare with the experimental data which is model dependent. The analytical expressions of the partial width $\Gamma (t \to H^+ b) $ are derived and we compare with the data available at this energy range. We examine the limits on the new parameters $\lambda_{ij}$ from the validness of perturbation theory., Comment: 14 pages, 4 figures, Universidad Nacional de Colombia. typos corrected

We present a new supersymmetric version of the SU(3) otimes 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 CP-even Higgs boson can be moved up to 140 GeV., Comment: 6 pages, 2 figures, typo corrected and acknowledgements added

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 $muon factor and the decay width of$ \mu \to e\gamma $,$ $the following quite general bounds are obtained:$ 7.62\times 10^{-4}\lesssim \xi_{\mu \tau}^{2}\lesssim 4.44\times 10^{-2}, $ $\xi_{e\tau}^{2}\lesssim 2.77\times 10^{-14}$. Additionally, based on the processes $\tau \to \mu \gamma $, and $\tau \to \mu \mu \mu $, bounds on $\xi_{\tau \tau} $and $\xi_{\mu \mu} $are also gotten, such constraints on these parameters$ $still give enough room for either a strong suppression$ $or strong enhancement on the coupling of any Higgs boson to a pair of tau leptons or a pair of muons\textbf{.} Furthermore, upper limits on the decay widths of the leptonic decays $\tau \to e\gamma, $and $\tau \to eee $are calculated, finding them to stay far from the reach of near future experiments., Comment: Departamento de Fisica, Universidad Nacional de Colombia, Bogota, Colombia. 12 pages, 2 figures

We give explicit formulae for the anomalous chromomagnetic dipole moment of the top quark in the framework of the standard model, the two higgs doublet model and the minimal supersymmetric standard model. Finally, we compare the results for this coupling with the bound -0.03 <= Delta kappa <= 0.01 coming from analysis of b --> s gamma process whith an on-shell gluon., Comment: Presented at the XXII Physics in Collisions Conference (PIC02), Stanford, Ca, USA, June 2002, 3 pages, LaTeX, 2 eps figures

The anomalous chromomagnetic moment of the top quark arises from one loop corrections to the vertex $\bar t t g$. We give explicit formulae 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 $-0.03 \leq \Delta \kappa \leq 0.01$ emerging from the analysis of $b \to s \gamma$ process with an on-shell bremsstrahlung gluon. This enables us to study the allowed region of parameters of the models under consideration., Comment: RevTex4, Version to appear in Phys. Rev. D

We consider the branching ratio for the process $t \to c \gamma$ in the context of the General Two Higgs Doublet Model type III. We find that taking into account reasonable values for the parameter $\tan \beta$ is possible to get values of this branching ratio up to orders of magnitude lying in the range of sensitivity of near future top quark experiments. For values of $B(t \to c \gamma) \sim 1-9 \times 10^{-5}$, values between 8-15 for $\tan \beta$ are allowed., Comment: 12 pages, 3 eps figures, RevTex4

Current muon anomalous magnetic moment data have challenged the SM, and seems to open a window to new Physics. Since the difference between SM and experimental predictions is approximately $2.6\sigma$. In the framework of the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous magnetic moment to get lower and upper bounds for the Flavor Changing Yukawa couplings (FC) in the leptonic sector. We also obtain lower bounds for the mass of the Pseudoscalar Higgs ($m_{A^ 0}$, as a function of the parameters of the model., Comment: 9 pages, 5 figures

Current experimental data from the $g-2$ muon factor, seems to show the necessity of physics beyond the Standard Model (SM), since the difference between SM and experimental predictions is 2.6$\sigma $. In the framework of the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous magnetic moment to get lower and upper bounds for the Flavour Changing (FC) Yukawa couplings in the leptonic sector. We also obtain lower bounds for the mass of the pseudoscalar Higgs ($m_{A^0}$) as a function of the parameters of the model., Comment: 12 pages, RevTex4, 5 figures. Improved presentation, updated experimental data, amplified analysis, new figures added. Subbmited to Phys. Rev. D

We consider the Two Higgs Doublet Model (2HDM) of type III which leads to Flavour Changing Neutral Currents (FCNC) at tree level in the leptonic sector. In the framework of this model we can have, in principle, two situations: the case (a) when both doublets acquire a vacuum expectation value different from zero and the case (b) when only one of them is not zero. In addition, we show that we can make two types of rotations for the flavor mixing matrices which generates four types of lagrangians, with the rotation of type I we recover the case (b) from the case (a) in the limit $\tan \beta \to \infty $, and with the rotation of type II we obtain the case (b) from (a) in the limit $\tan \beta \to 0. $Moreover, two of the four possible lagrangians correspond to the models of types I and II plus Flavor Changing (FC) interactions. The analitical expressions of the partial lepton number violating widths $\Gamma (\mu \to eee) $ and $\Gamma (\mu \to e\gamma) $are derived for the cases (a) and (b) and both types of rotations.$ $In all cases these widths go asymptotically to zero in the decoupling limit for all Higgses. We present from our analysis upper bounds for the flavour changing transition $\mu \to e,$ and we show that such bounds are sensitive to the VEV structure and the type of rotation utilized., Comment: 7 pages RevTeX4, 4 figures postscript, new section added and some new references

We study the dominant decays of the lightest Higgs boson in models with 2 and 3 Higgs doublets, for the case when its couplings to fermions are absent at tree-level. It is found that the branching ratio for the decay $H\to \gamma\gamma$ is above the one into fermion pairs, which is evaluated also at the 1-loop level., Comment: Universidad Nacional de Colombia, Depto. de Fisica,8 pages, 2 figures

We analyze the vertex Zff in the framework of models that add a new bottom quark in a nonsequential way and we evaluate the tree level contribution to LEP/SLC data $R_{b}$, $R_{l}$ and the total Z width $\Gamma_{Z}$. We obtain bounds for the mixing angles through the experimentally allowed contour regions of the parameters $\Lambda_{L,R}$ introduced here. In order to get a more restrictive region, we also consider the experimental results for $B\to \nu \nu X$ as well., Comment: 5 pages, LateX,1 figure: eps format, 3 tables. Final version, to appear in Physical Review D

We study the effects on the leptonic asymmetries A_{FB}, A_{pol} and A_{LR} coming from a model of compositeness. We consider the effects coming from the self-energies and the vertex correction to $Z l^+ l^-$. Thus we use the Altarelli parametrization of the oblique corrections. We get the asymptotic limits of these corrections in terms of the parameters $(m^*, \Lambda, f, f')$ and we get bounds for the quotient $m^*/\Lambda$ with different values of $(f, f')$. We conclude that both asymmetries produce bounds for such quotient when $f'$ overweigth to $f$, and this fact is related with the breakdown of the custodial symmetry., Comment: Latex, 13 pages, 4 figures

We calculate the one loop corrections to the chromomagnetic dipole moment of the top quark in the framework of the Standard Model, the two Higgs doublet model and the Minimal Supersymmetric Standard Model. In the Standard Model we consider the QCD and the electroweak corrections generated by gluon and Higgs boson exchanges, respectively. In the Minimal Supersymmetric Standard Model, we calculate the SUSY- QCD corrections, including the mixing effects between the stop coming from the left- and right-handed sectors. We obtain that the Standard Model contribution is of the order of -0.004< delta kappa_g^t < -0.001, and the values for diferents scenarios are of the order of -0.001 < \delta \kappa_g^t < -0.01., Comment: Latex file, 15 pages, 5 ps figures

Using the CLEO data for $b\to s\gamma$, we constrain the chromomagnetic dipole moment of the top quark within the context of a decoupling effective Lagrangian approach. Our results are in agreement with the results obtained for the $e^+e^-$ and hadron colliders.