Aspects of top quark physics can be studied at a future Circular Electron-Positron Collider (CEPC). In particular, Flavor-Changing Neutral Current interactions (FCNC) of the top quark can be studied even with a center-of-mass energy from $\sqrt{s}\gtrsim m_t$ to $\sqrt{s}=240$ GeV, through the production a single top quark in association with a charm quark, which can arise in several scenarios of new physics. We explore here this signal within the Left-Right Mirror Model, which is a Left-Right model that includes mirror fermions; this model is motivated as a possible solution to the strong CP problem and by its rich phenomenology. We find that for particular scenarios of the model parameters, which are in agreement with the most up-to-date experimental constraints, the signal coming from the process $e^+e^-\to V \to tc$ ($V=Z,\,Z^{\prime}$) provide a detectable signal and thus it can give evidence for FCNC interactions; in these scenarios the mass of a new neutral gauge boson can be as high as $m_{Z'}=7$ TeV.
The top quark flavor changing neutral current (FCNC) processes are extremely suppressed within the Standard Model (SM) of particle physics. However, they could be enhanced in a new physics model Beyond the Standard Model (BSM). The top quark FCNC interactions would be a good test of new physics at present and future colliders. Within the framework of the BSM models, these interactions can be described by an effective Lagrangian. In this work, we study tqgamma and tqZ effective FCNC interaction vertices through the process e-p->e-Wq+X at future electron proton colliders, projected as Large Hadr…
We investigate the flavour changing neutral currents (FCNC) generated by dimension six four-fermion operators at the Large Hadron-Electron Collider (LHeC) proposed at CERN in an effective approach. This is performed by monte carlo analysis at the full detector level, as the background is successfully reduced by using invariant mass scheme to require the final states to reconstruct the mass (transverse mass) of the top quark (W boson). Our analysis shows that the future electron proton colliders like the LHeC can probe competitive limits for the top FCNC dimension six four fermion operators suc…
Flavour changing neutral currents are absent at tree level in the Standard Model (SM) and are highly suppressed at higher orders due the Glashow-Iliopoulos-Maiani mechanism. Hence, any evidence of such currents related to the top quark will definitely signal new physics beyond the SM. In this work we will discuss how an electron-positron collider can contribute to the field after the Large Hadron Collider (LHC) has collected at least 100 fb^{-1} of integrated luminosity operating at sqrt{s} = 14 TeV.
In this paper, we consider a single top quark production in association with a neutral gauge boson (Z boson or Photon) at the future electron-positron colliders. We utilize these channels to probe the top quark Flavour Changing Neutral Currents (FCNC) interactions in $tqZ$ and $tqγ$ vertices. We perform two separate analyses for top-Z-jet and top-$γ$-jet channels. The Standard Model Effective Field Theory (SMEFT) approach is employed to search for these anomalous couplings. We consider parton showering, hadronization and fast detector simulation in our study and use a cut-and-count technique t…
We study the discovery potential of the flavor-changing neutral coupling (FCNC) htc of the Higgs boson and the top quark through the rare tree-body decay h -> Wbc at Muon colliders for a light Higgs boson with mass 114 < m_h < 145 GeV. This decay mode may compete with the SM background induced by the hWW coupling in some models with a tree-level htc coupling and with models that predict this coupling at the one-loop level in the range 10^{-2} - 10^{-1}. A future muon collider could test the scalar FCNC decay t -> hc via Higgs decay h -> t* c -> b W+ c down to values of the coupling g_{tc}=0.5 …
We systematically calculate various flavor-changing neutral-current top-quark processes induced by supersymmetry at the Large Hadron Collider, which include five decay modes and six production channels. To reveal the characteristics of these processes, we first compare the dependence of the rates for these channels on the relevant supersymmetric parameters, then we scan the whole parameter space to find their maximal rates, including all the direct and indirect current experimental constraints on the scharm-stop flavor mixings. We find that, under all these constraints, only a few channels, th…
We investigate the anomalous flavour changing neutral current (FCNC) interactions of top quark through the process $e^{-}p\to e^{-}W^{\pm}q+X$. We calculate the signal and background cross sections in electron proton collisions at Large Hadron electron Collider (LHeC) with a 7 TeV proton beam from the LHC and a new 60 GeV electron beam from energy recovery linac (ERL). We study the relevant background processes including one electron and three jets in the final state. The distributions of the invariant mass of two jets and an additional jet tagged as $b$-jet are used to account signal and back…
We study the FCNC top quark decays t -> c h in the framework of the MSSM, where h= h^0,H^0,A^0 is any of the supersymmetric neutral Higgs bosons. We include the leading set of SUSY-QCD and SUSY electroweak contributions. While the FCNC top quark decay into the SM Higgs boson has such a negligible rate that will not be accessible to any presently conceivable accelerator, we find that there is a chance that the potential rates in the MSSM can be measured at the high luminosity colliders round the corner, especially at the LHC and possibly at a future LC, but we deem it difficult at the upgraded …
We calculate flavor-changing neutral-current (FCNC) processes involving top-quark production via anomalous tqV couplings at the Tevatron and HERA colliders. We cover the FCNC processes p pbar -> t Z, p pbar -> t gamma, p pbar -> t t, and e p -> e t. We go beyond leading order and include the effects of soft-gluon corrections through next-to-next-to-leading order. We demonstrate the stabilisation of the cross section with respect to the variation of QCD scale, and we investigate the reach of the Tevatron and HERA colliders.
We present the complete next-to-leading order (NLO) QCD corrections to the top quark associated with $γ$ production induced by model-independent $tqγ$ and $tqg$ flavor-changing neutral-current (FCNC) couplings at hadron colliders, respectively. We also consider the mixing effects between the $tqγ$ and $tqg$ FCNC couplings for this process. Our results show that, for the $tqγ$ couplings, the NLO QCD corrections can enhance the total cross sections by about 50% and 40% at the Tevatron and LHC, respectively. Including the contributions from the $tqγ$, $tqg$ FCNC couplings and their mixing effects…
We calculated the next-to-leading order (NLO) QCD corrections to the cross sections for direct top quark productions induced by model--independent flavour changing neutral current couplings at hadron colliders. The NLO results increase the experimental sensitivity to the anomalous couplings. Our results show that the NLO QCD corrections enhance the leading order (LO) total cross sections at the Tevatron Run 2 about 60% for both of $κ_{tc}^g$ and $κ_{tu}^g$ couplings, and enhance the LO total cross sections at the LHC about 40% for $κ_{tc}^g$ couplings and 50% for $κ_{tu}^g$ couplings, respecti…
In supersymmetry (SUSY) the flavor mixing between top-squark (stop) and charm-squark (scharm) induces the flavor-changing neutral-current (FCNC) stop decay $\tilde t_1 \to c \tilde χ^0_1$. Searching for this decay serves as a probe of soft SUSY breaking parameters. Focusing on the stop pair production followed by the FCNC decay of one stop and the charge-current decay of the other stop, we investigate the potential of detecting this FCNC stop decay at the Fermilab Tevatron, the CERN Large Hadron Collider (LHC) and the next-generation $e^+e^-$ linear collider (LC). We find that this decay may n…
We study the potential impacts of a new type of particle collider -- an $eμ$ collider -- on the search for new physics beyond the Standard Model. As our first attempt for exploring its physics potential, we demonstrate that the the $eμ$ collision experiment can be highly efficient in searching for lepton-number-violating Flavor Changing Neutral Current phenomena.
We perform an updated analysis on the searches for the anomalous FCNC Yukawa interactions between the top quark, the Higgs boson, and either an up or charm quark ($\rm tqh,\ q=u,\ c$). We probe the observability of the FCNC top-Higgs couplings through the processes $\rm e^- p\rightarrow ν_e \bar{t} \rightarrow ν_e h \bar{q}$ (signal.I) and $\rm \ e^- p \to ν_e h b$ (singal.II) at the proposed electron proton (ep) colliders, where the Higgs boson decays to a $\rm b\bar{b}$ pair. We find that at the high luminosity (1 $\rm ab^{-1}$) ep colliders where the electrons have a polarisation of $\rm 80…
We discuss FCNC top quark production via anomalous tqV couplings at the Tevatron and HERA colliders. We calculate higher-order soft-gluon corrections to such processes and demonstrate the stabilization of the cross section when these corrections are included.
In this report, instead to give comprehensive review on two important research fields during my first term postdoctoral working period: Higgs and FCNC physics, I will collect part of my recently works on it. Charged Higgs is the distinguished signature of new physics, in this report, I review my two works on charged Higgs associated production with top quark and $W$ boson at hardron colliders. Our researches show that these two charged Higgs production mechanisms are important channel not only in finding charged Higgs, but also in studying the quantum structure of new physics. Flavor Changing …
In the most general two-Higgs doublet model (generally referred to as Model III), tree level flavor changing neutral couplings exist. It has been noted that the most natural value for such a coupling is of the order of the geometric mean of the Yukawa couplings of the two fermions. Bounds on those couplings that involve the second and third generations, from $τ,B,D$ and $μ$ physics, are very weak and are not sensitive to this "natural" value. In this paper, it is pointed out that the process μμ---> μτ, at a muon collider tuned to the scalar resonance, will easily reach this sensitivity if the …
A study of single top quark production via flavor changing neutral current interactions at $tqγ$ vertices is performed at future circular hadron electron collider. The signal cross sections for the processes $e^{-}p\to e^{-}W^{\pm}q+X$ and $e^{-}p\to e^{-}W^{\pm}bq+X$ in the collision of electron beam with energy $E_e=$ 60 GeV and proton beam with energy $E_p=$ 50 TeV are calculated. In the analysis, the invariant mass distributions of three jets reconstructing top quark mass, requiring one b-tagged jet and other two jets reconstructing the $W$ mass are used to count signal and background even…
We briefly review the studies on the top quark FCNC processes at a next-generation linear collider. Such processes, including various FCNC top quark rare decays and top-charm associated productions, are extremely suppressed in the standard model (SM) but could be significantly enhanced in some extensions. We compared the predictions from different typical new physics models: the SM, the minimal supersymmetric model (MSSM), the general two-higgs-doublet model (2HDM) and the topcolor-assisted technicolor (TC2) model. Our conclusion is: (1) While all the new physics models can enhance the rates b…
We calculate first-order QCD corrections to the cross section for single top quark production mediated by flavor changing neutral currents (FCNC) in ep collisions at the HERA collider. We find that the uncertainty due to the choice of the QCD scale is significantly reduced. This study is motivated by the current experimental work for limits on the FCNC single top cross section.
The top quark is the heaviest particle to date discovered, with a mass close to the electroweak symmetry breaking scale. It is expected that the top quark would be sensitive to the new physics at the TeV scale. One of the most important aspects of the top quark physics can be the investigation of the possible anomalous couplings. Here, we study the top quark flavor changing neutral current (FCNC) couplings via the extra gauge boson Z' at the Large Hadron Collider (LHC) and the Compact Linear Collider (CLIC) energies. We calculate the total cross sections for the signal and the corresponding St…
In this paper, we study the anomalous flavor changing neutral current Yukawa interactions between the top quark, the Higgs boson, and either an up or charm quark ($\rm tqH, q=u, c$). We probe these couplings in $\rm e^- p\rightarrow ν_e \bar{t} \rightarrow ν_e H \bar{q}$ and the channel $\rm e^- p \rightarrow ν_e H b$. Both channels are induced by charged current interactions through $\rm e^- p$ collision at the Large Hadron Electron Collider(LHeC). We study the signatures with the Higgs decay modes $\rm H\rightarrow γγ, b\bar{b}$ and $τ^+τ^-$. Our results show that the flavor changing couplin…
In the Minimal Supersymmetric Model (MSSM) the hitherto unconstrained flavor mixing between top-squark and charm-squark will induce the flavor-changing neutral-current (FCNC) interaction between top quark and charm quark, which then give rise to various processes at the next generation linear collider (NLC), i.e., the top-charm associated productions via $e^+ e^-$, $e^- γ$ and $γγ$ collisions as well as the top quark rare decays $t \to c V$ ($V=g$, $γ$ or $Z$). All these processes involve the same part of the parameter space of the MSSM. Through a comparative analysis for all these processes a…
We calculate single top-quark production at hadron colliders via the chromo-magnetic flavor-changing neutral current couplings $\bar tcg$ and $\bar tug$. We find that the strength for the anomalous $\bar tcg$ ($\bar tug$) coupling may be probed to $κ_c / Λ= 0.092 {TeV}^{-1}$ ($κ_u / Λ= 0.026 {TeV}^{-1}$) at the Tevatron with $2 {fb}^{-1}$ of data and $κ_c / Λ= 0.013 {TeV}^{-1}$ ($κ_u / Λ= 0.0061 {TeV}^{-1}$) at the LHC with $10 {fb}^{-1}$ of data. The two couplings may be distinguished by a comparision of the single top signal with the direct top and top decay signals for these couplings.
We study the nature of the flavor changing neutral couplings of the top quark with the Higgs boson and the up/charm quark in the $t\bar{t}$ production at linear colliders. There are previous bounds on such tqH couplings at both, linear and hadronic colliders, with the assumption that it couples equally to the left and the right handed fermions. In this paper we examine the chirality of the tqH coupling and construct different observables which will be sensitive to it. The kinematics of the emitted q from t $\rightarrow$ qH in $t\bar{t}$ production is discussed and it was found that the polar a…
Using the constraint on the single top production cross-section obtained at the HERA collider, $σ(ep \to e t X)$, we evaluate an upper limit on oupling constant of the anomalous top quark interaction with a gluon via flavor-changing neutral current: $|κ_{tgq}/Λ| \le 0.4 {TeV}^{-1}$, BR$(t \to gq) < 13 % $
Top quark and Higgs boson decays induced by flavor-changing neutra currents (FCNC) are very much suppressed in the Standard Model (SM). Their detection in colliders like the Large Hadron Collider (LHC), Next Linear Collider (NLC) or Tevatron would be a signal of new physics. We evaluate the FCNC decays t \to H^0 + c, t \to Z + c, and H^0 \to t + {\bar c} in the context of Alternative Left-Right symmetric Models (ALRM) with extra isosinglet heavy fermions; in this case, FCNC decays occurs at tree-level and they are only suppressed by the mixing between ordinary top and charm quarks, which is po…
We calculate the contribution of anomalous top-quark interaction with a gluon, photon, and $Z$-boson (FCNC) to $t \bar t$ pair production in hadronic collisions. Using the current data from Run~1 of the Tevatron we evaluate the upper limit on the the anomalous coupling of $t$-quark with gluon, $|κ_g/Λ| \le 0.52$ TeV$^{-1}$. We examine the production of double top ($t t$ or $\bar t \bar t$) at hadronic colliders as a result of FCNC interactions of the top quark. It is shown that the study of such reactions at LHC collider makes possible to obtain the constraint on strength of coupling at the le…
We investigate the sensitivity of future searches for the top-Higgs boson Flavour Changing Neutral Current (FCNC) couplings $tqh$~($q= u, c$) at the proposed High Energy Large Hadron Collider~(HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh). We perform a full simulation for two processes in the $h\to γγ$ decay channel (where $h$ is the discovered Higgs state): single top quark FCNC production in association with the Higgs boson (plus a jet) and top quark pair production with FCNC decays $t\to qh$. All the relevant backgrounds are considered in a cut based analysis to obtain…
Our main aim in this paper is to present detailed studies to probe the top quark flavor changing neutral current (FCNC) interactions at $tqg$, $tqγ$, $tqH$ and $tqZ (σ^{μν}, γ_μ)$ vertices in the triple-top signal $p p \to t \bar t t \, (\bar t t \bar t)$ at the high energy proposal of Large Hadron Collider (HE-LHC) and future circular hadron-hadron collider (FCC-hh). To this end, we investigate the production of three top quarks which arises from the FCNC couplings taken into account the fast simulation at $\sqrt{s} = 27$ TeV of HE-LHC and 100 TeV of FCC-hh considering the integrated luminosi…
In this thesis we discuss the combined effects of strong and electroweak FCNC effective operators in top quark physics at the CERN LHC and lepton flavour violation at the ILC with dimension six effective operators.
In this study we examine both anomalous magnetic and dipole moment type couplings of a heavy quark via its single production with subsequent dominant Standard Model decay modes at the Compact Linear Collider (CLIC). The signal and background cross sections are analyzed for heavy quark masses 600 and 700 GeV. We make the analysis to delimitate these couplings as well as to find the attainable integrated luminosities or 3$σ$ observation limit.
We revise the limits on the FCNC higgses in manifestly left-right symmetric theories. It is shown that the combination of the Kobayashi-Maskawa CP-violation with the tree level $ΔS=2$ higgs exchange gives very large contribution to the CP-violating $ε$ parameter. It leads to the new strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of the order $\sqrt{m_t/m_c}$. Being addressed to the supersymmetric left-right models, FCNC problem requires both right-handed scale and supersymmetric mass parameters be heavier than 50 TeV for $tanβ\sim 1$. The most relaxed case correspo…
The Effective Field Theory (EFT) approach is widely used in the search for possible deviations from the predictions of the Standard Model. Such an approximation of possible BSM physics is valid up to a certain levels of energy scale and accuracy. In this article, we investigate potential limitation of the EFT approach related to unitarity to describe possible contributions of flavor changing neutral currents (FCNC) involving the top quark. The numerical and analytical calculations of the FCNC processes used in the EFT approach demonstrate the constant asymptotic behavior of the total cross sec…
We present a study to examine the sensitivity of a future $e^{-} e^{+}$ collider to the anomalous top flavour-changing neutral current (FCNC) to the gluon. To separate signal from background a multivariate analysis is performed on top-quark pair and background events, where one top quark is considered to follow the dominant Standard Model (SM) decay, $t \rightarrow Wb$, and the other top decays through FCNC, $t\rightarrow qg$, where $q$ is a $u-$ or a $c-$quark. The analysis of fully-hadronic FCNC decay of the $t \bar{t}$ pair is also presented. The $95\%$ confidence level limits on the top-qu…
A study of the top quark \emph{Flavour Changing Neutral Current} (FCNC) through $Z$-boson has been performed in the proposed future $e^-p$ collider for the energy, $E_{e(p)} = 60~(7000)$~GeV. We considered an effective theory where the anomalous FCNC couplings are of vector and tensor nature. The effect of these couplings is probed in the single top production along with the scattered electron. The polar angle $θ$ of the electrons coming out of the primary vertex in association with the top quark polarization asymmetries constructed from the angular distribution of the secondary lepton arising…
The best limit on the strong FCNC anomalous couplings was obtained using the direct top production process at the Large Hadron Collider by the ATLAS collaboration. We perform a similar analysis but using a next-to-leading order generator, MEtop. We then show how the limits could be improved if the FCNC single top process $pp \to tj$ would be included as signal. Finally we discuss a slightly modified analysis with an extra hard jet in the final state.
We investigate the top quark anomalous Flavor Changing Neutral Current (FCNC) $tqg$ interactions to probe limits on the couplings $ζ_c$ and $ζ_u$ through the $qg \to lνb$ signal suprocess at FCC-hh collider with center of mass energy of 100 TeV. To separate signal from relevant Standard Model background processes, selection criteria based on Boosted Decision Trees (BDT) is used with a set of useful kinematic variables. The sensitivities on the anomalous top FCNC couplings $ζ_u$ and $ζ_c$ are found to be $1.239\times10^{-4}$ and $1.149\times10^{-4}$ for FCC-hh with $L_{int}$=10 ab$^{-1}$ at 95 …
We have studied the sensitivity to flavor changing neutral current interaction of top and Higgs boson at the future circular collider in the hadron-hadron collision mode (FCC-hh). Our main concerns are the processes of $pp\rightarrow th$ (FCNC production) and $pp\rightarrow t\bar{t}$ (one top FCNC decay) which contributes to the single lepton, at least three jets and the missing energy transverse in the final state. On the one hand FCC-hh offers very high luminosity and large cross section for these signal processes, on the other hand signal can be distinguished from background which needs app…
The large number of top quarks produced at the LHC and possible future hadron colliders allows to study rare decays of this particle. In many well motivated models of new physics, for example in non-minimal composite-Higgs models, the existence of scalar singlets can induce new flavor-violating top decays surpassing the Higgs contribution by orders of magnitude. We study the discovery prospects of rare top decays within such models and develop new search strategies to test these interactions in top pair-produced events at the LHC. We demonstrate that scales as large as $10$--$50$ TeV can be pr…
In this paper, we study the observability of the top-Higgs flavor changing neutral current (FCNC) $tqh$ coupling through the process $pp\to qg\to t(\to \ell^{+}bν)h(\to γγ)$ at the Large Hadron Collider~(LHC), where $\ell=e, μ$. Our numerical results show that, in some parameter regions, the LHC may observe the above signals at the $5σ$ level. Otherwise, the branching ratios $Br(t\to uh)$ and $Br(t\to ch)$ can be respectively probed to $0.036\%$ and $0.13\%$ at $3σ$ level at 14 TeV LHC with the high integrated luminosity of 3000 fb$^{-1}$. On the other hand, studying the charge ratio for the l…
We analyze the production and subsequent decay of the neutral MSSM Higgs bosons (h = h^0, H^0, A^0) mediated by flavor changing neutral currents (FCNC) in the LHC collider. We have computed the h-production cross-section times the FCNC branching ratio, σ(pp -> h -> qq') = σ(pp -> h) B(h -> qq'), in the LHC focusing on the strongly-interacting FCNC sector. Here qq' is an electrically neutral pair of quarks of different flavors, the dominant modes being those containing a heavy quark: tc or bs. We determine the maximum production rates for each of these modes and identify the relevant regions of…
We consider the Higgs boson anomalous FCNC interactions with $u$, $c$, $d$, $s$ and $b$ quarks using the effective field theory framework. Constraints on anomalous couplings are derived from experimental results on Higgs boson production with subsequent decay into $b \bar{b}$ pair at LHC with $\sqrt{s} = 13 $~TeV. Upper limits on the branching fractions of $H \to b\bar{s}$ and $H \to b\bar{d}$ are set by performing a realistic detector simulation and accurately reproducing analysis selections of the CMS Higgs boson measurement in the four-lepton final state at $\sqrt{s} = 13$ TeV. The searches…
FCC-hh is a proposed future energy-frontier hadron collider, which goal is to provide high luminosity proton collisions at a centre-of-mass energy of 100 TeV. The FCC-hh has an extremely rich physics program ranging from standard model (SM) measurements to direct searches for physics beyond the standard model (BSM). One of the processes sensitive to new physics is flavour-changing neutral currents (FCNC) that extremely rare in the SM but have enhanced behavior in several BSM scenarios. In this report we present results of projections of FCNC searches in top quark interactions to the FCC-hh con…
The single production of top quark due to flavor changing neutral current (FCNC) interaction and its decay to bW are studied at CLIC+LHC based gamma-p colliders. We consider both t-c-gamma and t-u-gamma anomalous couplings. The anomalous charm (up) quark anomalous coupling parameter kappa_gamma^c (kappa_gamma^u) can be probed down to 9.5x10^-3 (8.0x10^-3) at a gamma-p collider with sqrt{s_ep}=6.48 TeV and L_int=100 fb^-1.
If the underlying flavor symmetry is Abelian, quark mixings in $d_R$ sector are the most prominent. Such flavor violating effects can reveal itself through $\tilde d_R$ squark mixings if supersymmetry is realized in Nature. Quark-squark alignment is necessary to deal with $Δm_K$ and $ε_K$ constraints, but interestingly, with $m_{\tilde q}$, $m_{\tilde g} \sim$ TeV, the $\tilde d_R$ mixing effects are comparable to $B_d$ and $B_s$ mixings in the Standard Model, while $D^0$ mixing is tantalizingly close to some hints from data. CP phases in these mixings would therefore be deviant, and $| V_{td}…
In the framework of the Standard Model Effective Field Theory, we compare the lower bounds on the scale of new physics possibly contributing to the $f\bar{f}h$ effective couplings, obtained from the measurements of different observables, under the assumption that the Wilson coefficients of the relevant dim 6 operators respect certain flavour structure: either the Minimal Flavour Violation (MFV) ansatz or a flavour symmetry, often invoked to explain the observed pattern of fermion masses and mixings. We perform a global analysis of the bounds following from the limits on the diagonal couplings …
We study the flavor changing neutral current couplings of new heavy quarks through the Z' models at the LHC. We calculate the cross sections for the signal and the corresponding standard model background processes. Considering the present limits on the mass of new heavy quarks and the Z' boson, we performed an analysis to investigate the parameter space (mixing and mass) through different Z' models. For an FCNC mixing parameter x=0.1 and the Z' mass M_{Z'}=2000 GeV, and new heavy quark mass m_{t'}=700 GeV at the LHC with \sqrt{s}=13 TeV, we find the cross section for single production of new h…
There is no tree-level flavor changing neutral current (FCNC) in the standard model (SM) which contains only one Higgs doublet. If more Higgs doublets are introduced for various reasons, the tree level FCNC would be inevitable except extra symmetry was imposed. Therefore FCNC processes are the excellent probes for the physics beyond the SM (BSM). In this paper, we studied the lepton flavor violated (LFV) decay processes $h\rightarrowμτ$ and $τ\rightarrowμγ$ induced by Higgs-$μ$-$τ$ vertex. For $τ\rightarrowμγ$, its branching ratio is also related to the $ht\bar{t}$, $hτ^+τ^-$ and $hW^+W^-$ ver…
Measurements of single top and rare top quark production may be sensitive to theories of physics beyond the standard model (SM), including those in which the energy scale of new physics is beyond the energies directly accessible at the Large Hadron Collider. Such models may be observable through signatures like forbidden SM interactions or deviations of the top quark's couplings from the SM predictions. An overview of recent searches from the ATLAS and CMS Collaborations is presented, with a focus on flavor-changing neutral currents.
Higgs boson decays mediated by flavor changing neutral currents (FCNC) are very much suppressed in the Standard Model, at the level of 10^{-15} for Higgs boson masses of a few hundred GeV. Therefore, any experimental vestige of them would immediately call for new physics. In this paper we consider the FCNC decays of Higgs bosons into a top quark in a general two-Higgs-doublet model (2HDM). The isolated top quark signature, unbalanced by any other heavy particle, should help to identify the potential FCNC events much more than any other final state. We compute the maximum branching ratios and t…
We study the production of a single top quark in association with a heavy extra $Z'$ at hadron colliders in new physics models with and without flavor-changing neutral-current (FCNC) couplings. We use QCD soft-gluon resummation and threshold expansions to calculate higher-order corrections for the total cross section and transverse-momentum distributions for $t Z'$ production. The impact of the uncertainties due to the structure of the proton and scale dependence is also analyzed.
In the minimal supersymmetric model the R-parity violating top quark interactions, which are so far weakly constrained, can induce various flavor-changing neutral-current (FCNC) productions for the top quark at the Large Hadron Collider (LHC). In this work we assume the presence of the B-violating couplings and examine their contributions to the FCNC productions proceeding through the parton processes cg -> t, gg -> t c_bar, cg -> tγ, cg -> t Z and cg -> t h. We find that all these processes can be greatly enhanced relative to the R-parity preserving predictions. In the parameter space allowed…
