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Register a new userRare top decay $trightarrow cgamma$ in general THDM-III
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Jose Halim Montes de Oca Yemha
Publication date
2014
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English
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We study the decay $trightarrow cgamma$ with flavor-changing neutral interactions in scalar sector of the type III Two Higgs Doublet Model (THDM-III) with mixing between neutral scalar fields as a result of considering the most general scalar potential. The branching ratio of the decay $Br(trightarrow cgamma)$ is calculated as function of the mixing parameters and masses of the neutral scalar fields. We obtain a $Br(trightarrow cgamma)$ of the order of $10^{-8}$ for the considered regions of the mixing parameters. Finally, one upper bound for the possible events is estimated to be $n=18$ by assuming a expected luminosity of the order of 300 $fb^{-1}$.
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We discuss the formalism of two Higgs doublet model type III with CP violation from CP-even CP-odd mixing in the neutral Higgs bosons. The flavor changing interactions among neutral Higgs bosons and fermions are presented at tree level in this type of model. These assumptions allow the study rare top decays mediated by neutral Higgs bosons, particularly we are interested in $trightarrow c l^+l^-$. For this process we estimated upper bounds of the branching ratios $textrm{Br}(trightarrow c tau^+tau^-)$ of the order of $10^{-9}sim 10^{-7}$ for a neutral Higgs boson mass of 125 GeV and $tanbeta=1$, 1.5, 2, 2.5. For the case of $trightarrow c tau^+tau^-$ the number of possible events is estimated from 1 to 10 events which could be observed in future experiments at LHC with a luminosity of 300 $textrm{fb}^{-1}$ and 14 GeV for the energy of the center of mass. Also we estimate that the number of events for the process $trightarrow c l^+l^-$ in different scenarios is of order of $2500$.
The flavor-changing top-quark decay $tto c h$, where $h$ is the lightest CP-even Higgs boson in the minimal supersymmetric standard model, is examined in the R-parity-violating supersymmetric model. Within the existing bounds on the relevant R-parity-violating couplings, the branching fraction for $tto c h$ can be as large as about $10^{-5}$ in some part of the parameter space.
As part of the search for new physics beyond the Standard Model, we chose the determination of the Higgs boson decay width as one of the least experimentally determined values. The decay widths into the four fermions of the lightest and heaviest CP-even Higgs bosons of the THDM model were calculated, taking into account QCD and electroweak corrections in the NLO approximation. To achieve this goal, the program Monte Carlo Prophecy 4f with special scenarios of parameters, 7B1 and 5B1 were used. It was found that the decay width of the heavier CP-even Higgs boson, H differs from H$_{SM}$ by 1227.93 times and changes to a negative value when deviating from the standard scenarios. Scale factors k$^2_{Z}$ and k$^2_{W}$ showed the predominance of the associated with Z boson production cross section of CP-even Higgs boson over the associated with W production cross section.
The rare top decay t-> c l+l-, which involves flavor violation, is studied as a possible probe of new physics. This decay is analyzed with the simplest Standard Model extensions with additional gauge symmetry formalism. The considered extension is the Left-Right Symmetric Model, including a new neutral gauge boson Z that allows to obtain the decay at tree level through Flavor Changing Neutral Currents (FCNC) couplings. The neutral gauge boson couplings are considered diagonal but family non-universal in order to induce these FCNC. We find the $BR(t-> c l+l-)~10^{-13} for a range 1 TeV < M_{Z} < 3 TeV.
The rare exclusive dileptonic $Lambda_{b}to Lambdaell^{+}ell^{-}$ $(ell =mu, tau)$ decays are investigated in the general two-Higgs-doublet model of type III. A significant enhancement to the branching ratios, differential branching ratios, leptons forward-backward asymmetry, and the $Lambda$ baryon polarizations over the standard model is obtained. Measurements of these quantities will be useful for establishing the two-Higgs doublet model.
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