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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 $2500$.
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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 $fb^{-1}$.
We discuss the prospects - within several models - for the observation of CP-violation (CPV) in top decays and production. The outlook looks best for t -> bW at the LHC (MSSM CPV), t -> b tau u_tau at TeV3, LHC and NLC (H^+ CPV), p p-bar -> t b-bar + X at TeV3 (MSSM CPV), p p -> t t-bar + X at the LHC (MSSM CPV and neutral Higgs CPV) and for e^+ e^- -> t t-bar h, t t-bar Z, where h is the lowest mass neutral Higgs boson, at an NLC with energy geq 1 TeV (neutral Higgs CPV).
Recent studies about CP violation in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters are reviewed. In order to unambiguously identify the CP-violating phenomena it is necessary to study CP-odd or T-odd observables. In chargino and neutralino production and decay at the International Linear Collider (ILC) triple product asymmetries and asymmetries defined via transverse beam polarization have been analyzed. It has been found that these asymmetries can be measured at the ILC in a large region of the MSSM parameter space and are thus an important tool to establish CP violation in supersymmetry.
Top quark is extremely sensitive to non-standard CP violating phases. General strategies for exposing different types of phases at the NLC are outlined. SUSY phase(s) cause PRA in $tto Wb$. The transverse polarization of the $tau$ in the reaction $tto btau u$ is extremely sensitive to a phase from the charged Higgs sector. Phase(s) from the neutral Higgs sector cause appreciable dipole moment effects and lead to sizable asymmetries in $e^+e^-to tbar tH^0$ and $e^+e^-to tbar t u_ebar u_e$.}]
The radiative decay of neutral fermions has been studied for decades but $CP$ violation induced within such a paradigm has evaded attention. $CP$ violation in these processes can produce an asymmetry between circularly polarised directions of the radiated photons and produces an important source of net circular polarisation in particle and astroparticle physics observables. The results presented in this work outlines the general connection between $CP$ violation and circular polarisation for both Dirac and Majorana fermions and can be used for any class of models that produce such radiative decays. The total $CP$ violation is calculated based on a widely studied Yukawa interaction considered in both active and sterile neutrino radiative decay scenarios as well as searches for dark matter via direct detection and collider signatures. Finally, the phenomenological implications of the formalism on keV sterile neutrino decay, leptogenesis-induced right-handed neutrino radiative decay and IceCube-driven heavy dark matter decay are discussed.
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