Among other roles the LHC will play a role of the top "factory" and it will give us unique possibility to study new physics signatures in different ways. Many scenarios of new physics allow top quark FCNC decays. Using most general model independent Lagrangian of new physics we investigate possible experimental signals of new physics in t --> c(u) l+ l- FCNC top decays. We find that measurement of two possible asymmetries might give very important and interesting information of NP. It is particularly interesting to use them to discriminate among variety on NP scenarios. We consider also contributions of the interference between scalar and vector mediators of the FCNC decays.
We present a new Monte Carlo generator for Direct top and Single top production via flavour-changing neutral currents (FCNC). This new tool calculates the cross section and generates events with Next-to-Leading order precision for the Direct top process and Leading-Order precision for all other FCNC single top processes. A set of independent dimension six FCNC operators has been implemented - including four-fermion operators - where at least one top-quark is present in the interaction.
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.
Electroweak baryogenesis in a two-Higgs doublet model is a well-motivated and testable scenario for physics beyond the Standard Model. An attractive way of providing $CP$ violation is through flavor-changing Higgs couplings, where the top-charm coupling is hardly constrained. This minimal scenario can be tested by searching for heavy charged and neutral Higgs bosons at the LHC. While the charged Higgs signature requires a dedicated analysis, the neutral Higgs signature will be covered by a general search for same-sign top pairs. Together, they provide a conclusive test of this kind of baryogen…
Top quark flavor changing neutral current (FCNC) interactions are highly suppressed in the Standard Model. Therefore, any large signal of FCNCs will indicate the existence of new interactions. In this paper, searches for FCNC interactions in top quark production and decay at the Tevatron and LHC are presented. FCNC searches in $t\rightarrow qZ$ and $t\rightarrow Hq$ decays, and in top quark production in $pp\rightarrow t+j$, $pp\rightarrow t+Z$ are summarized. Effect of top quark FCNCs on single top quark cross-section, and the searches for same-sign top quark pair production through FCNCs are…
Rare flavour changing neutral current (FCNC) decays of top, beauty and charm quarks can provide a powerful probe for as yet unobserved particles. Recent results on FCNC $b \to s$, $c \to u$ and $t$ transitions from the LHC experiments are reviewed. Particular attention is paid to the angular distribution of the $B^{0} \to K^{*0} μ^{+} μ^{-}$ decay, where a measurement performed by LHCb shows a local discrepancy of 3.7 standard deviations with respect to the SM prediction. Using the decay $B^{+} \to K^{+}π^{-}π^{+}γ$, LHCb have also been able to demonstrate the polarisation of photons produced …
In this paper we propose and study direct single top quark production channel for probing the tq$γ$ flavor-changing neutral current (FCNC) interactions at the LHC. We reinterpret the experimental results of a search for direct single top quark production performed by ATLAS collaboration at 8 TeV to set upper bounds on the FCNC top quark decay branching fractions through the proposed channel, resulting in ${\cal B}$(t$\rightarrow$ u$γ$) $<$ 0.05\% and ${\cal B}$(t$\rightarrow$ c$γ$) $<$ 0.14\%. Finally, the expected sensitivity at 13 TeV for various integrated luminosity scenarios is estimated.
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…
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…
In absence of any distinct evidence of new physics phenomena at the LHC, an increasing number of experimental studies aim at probing anomalous effects with an effective field theory (EFT) that represents a comprehensive approach for interpretation of various experimental results. The processes with the production of top quarks are sensitive to several classes of EFT operators including the flavour-changing neutral currents (FCNC). The summary of the latest CMS results based on the recent studies of the standard model processes and searches for new physics effects involving top quarks are prese…
We present a comprehensive analysis of the loop induced top quark FCNC signals at the LHC within one class of the simplified model. The loop level FCNC interactions are well motivated to avoid the hierarchy of the top quark couplings from the new physics and standard model. Such a theory will posit a Majorana dark matter candidate and could be tested through dark matter relic density, direct detection experiments (the scattering between dark matter and heavy nuclei), and the collider signals at the LHC. We find that the spin-independent (SI) scattering between Majorana dark matter and nuclei w…
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…
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.
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…
Since the top quark FCNC processes are extremely supressed in the Standard Model (SM) but could be greatly enhanced in some new physics models, they could serve as a smoking gun for new physics hunting at the LHC. In this brief review we summarize the new physics predictions for various top quark FCNC processes at the LHC by focusing on two typical models: the minimal supersymmetric model (MSSM) and the topcolor-assisted technicolor (TC2) model. The conclusion is: (1) Both new physics models can greatly enhance the SM predictions by several orders; (2) The TC2 model allows for largest enhancem…
We study the one-loop contribution of the effective flavor changing neutral couplings (FCNC) $tcZ$ to the charm quark electric dipole moment. Using the known limits on the top and charm quarks electric dipole moments, we place limits on these FCNC anomalous couplings.
The top quark is expected to be a probe to new physics beyond the standard model. Thanks to the large number of top quarks produced at the Tevatron and the LHC, various properties of the top quark can now be measured accurately. An effective field theory allows us to study the new physics effects in a model-independent way, and to this end accurate theoretical predictions are required. In this talk we will discuss some recent results on top-quark decay processes as well as flavor-changing processes, based on the effective field theory approach.
In this paper, we study the single top and Higgs associated production $pp \to thj$ in the presence of top-Higgs FCNC couplings($κ_{tqh}, q=u,c$) at the LHC. Under the current constraints, we find that the cross section of $pp \to thj$ can be sizably enhanced in comparison with the SM predictions at 8 and 14 TeV LHC. We also find that the full cross section of $pp \to thj$ with $κ_{tch}$ is larger than the resonant cross section of $pp \to t\bar{t} \to thj$ by a factor 1.16 at 8 TeV LHC and 1.12 at 14 TeV LHC, respectively. We further explore the observability of top-Higgs FCNC couplings throu…
Some interpretations of $R_{D^{(*)}}$ anomaly in $B$ meson decay using leptoquark (LQ) models can also generate top quark decays through Flavor Changing Neutral Current (FCNC). In this work we focus on two LQs, i.e. scalar $S_1$ and vector $U_1$ which are both singlet under the $SU(2)_L$ gauge group in the Standard Model (SM). We investigate their implications on the 3-body top FCNC decays $t\to c \ell_i \ell_j$ at tree level and the 2-body $t\to c V$ at one-loop level, with $\ell$ being the SM leptons and $V=γ, Z, g$ being the SM gauge bosons. We utilize the $2σ$ parameter fitting ranges of t…
We evaluate the top-quark FCNC productions induced by the topcolor assisted technicolor (TC2) model at the LHC. These productions proceed respectively through the parton-level processes g g -> t c_bar, c g->t, c g -> t g, c g -> t Z and c g -> t γ. We show the dependence of the production rates on the relevant TC2 parameters and compare the results with the predictions in the minimal supersymmetric model. We find that for each channel the TC2 model predicts a much larger production rate than the supersymmetric model. All these rare productions in the TC2 model can be enhanced above the 3-sigma…
The anomaly of the top quark forward-backward asymmetry $A^t_{FB}$ observed at the Tevatron can be explained by the t-channel exchange of a neutral gauge boson (Z') which has sizable flavor changing coupling for top and up quarks. This gauge boson can also induce the top quark flavor-changing neutral-current (FCNC) decays and the like-sign top pair production at the LHC. In this work we focus on two models which predict such a Z', namely the left-right model and the U(1)_X model, to investigate the correlated effects on $A^t_{FB}$, the FCNC decays $t -> u V$ ($V=g,Z,γ$) and the like-sign top p…
The topcolor-assisted technicolor (TC2) model predicts several pseudo-scalars called top-pions and at loop level they can induce the FCNC top quark decay t->cgg which is extremely suppressed in the Standard Model (SM). We find that in the allowed parameter space the TC2 model can greatly enhance such a FCNC decay and push the branching ratio up to 10^{-3}, which is much larger than the predictions in the SM (10^{-9}) and in the minimal supersymmetric model (10^{-4}). We also compare the result with the two-body FCNC decay t-> cg and find that the branching ratio of t-> cgg is slightly larger t…
We calculate flavor-changing neutral current (FCNC) processes with top-quark production via anomalous couplings at LHC energies. We report on progress on the FCNC processes gu -> tZ, gu -> t gamma and gu -> tg. We go beyond leading order and include soft-gluon corrections through next-to-next-to-leading order.
Flavor-changing neutral current (FCNC) top-quark decays are highly suppressed due to the Glashow-Iliopoulos-Maiani mechanism in the standard model (SM). If $t\to q h, qV$ with $V=g,γ, Z$ are all induced via quantum loop levels, then we investigate the effect that can enhance the top-FCNC up to the sensitivity designed at the high-luminosity (HL) LHC. Inspired by the mechanism of the scotogenic neutrino mass, we extend the SM by including $Z_2$-odd colored fermions when a $Z_2$ discrete is imposed. The results show that by taking $BR(t\to u g) \lesssim 0.61 \times 10^{-4}$ recently measured by …
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…
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 consider a Z' model where the Z' boson couples only to up and top quarks. As a simple setup, one can consider a family-dependent $U(1)'$ symmetry, under which only right-handed up-type quarks are charged. After symmetry breaking, the right-handed quarks mix with each other and top flavor-changing neutral currents (FCNCs) mediated by the Z' boson can be generated at tree level. We take into account several processes to probe the top FCNCs, and find that the same sign top quark pair production or the triple top quark production is the most capable of testing the top FCNCs. We also consider a …
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.
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.
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…
We study the possibility of same sign top quark pair production at the LHC (and the VLHC) as a direct probe of FCNC processes. Besides the SM neutral Z boson, two other neutral bosons are considered, a top-Higgs type scalar and a Z' boson that appear in Topcolor assisted Technicolor models. We find that the FCNC couplings tqV (q=u,c ; V=H,Z,Z') may produce an interesting signal of same sign top quark pairs that could be observed at the LHC (VLHC).
Motivated by the search for flavor-changing neutral current (FCNC) top quark decays at the LHC, we calculate rare Higgs three body decay $H\rightarrow Wbc$ induced by top-Higgs FCNC coupling in the littlest Higgs model with T-parity(LHT). We find that the branching ratios of $H\rightarrow Wbc$ in the LHT model can reach $\mathcal O(10^{-7})$ in the allowed parameter space.
Flavor changing neutral current (FCNC) interactions for a top quark $t$ decays into $Xq$ with $X$ represents a neutral gauge or Higgs boson, and $q$ a up- or charm-quark are highly suppressed in the Standard Model (SM) due to the Glashow-Iliopoulos-Miami mechanism. Whilst current limits on the branching ratios of these processes have been established at the order of $10^{-4}$ from the Large Hadron Collider experiments, SM predictions are at least nine orders of magnitude below. In this work, we study some of these FCNC processes in the context of an extended mirror fermion model, originally pr…
We study the effect that FCNC interactions of the top quark will have on the branching ratio of charged decays of the top quark. We have performed an integrated analysis using Tevatron and B-factories data and with just the further assumption that the CKM matrix is unitary we can obtain very restrictive bounds on the strong and electroweak FCNC branching ratios Br(t -> q X) < 4.0 10^{-4}, where X is any vector boson and a sum in q = u,c is implied.
The Large Hadron Collider is the world's largest and highest center-of-mass energy particle accelerator. During the Phase I operation it is expected that the LHC operated at a centre-of-mass energy of 13 TeV will deliver to the CMS experiment total integrated luminosity of $\sim$300 fb$^{-1}$ till 2023. The High Luminosity LHC upgrade is expected to run at a centre-of-mass energy of 14 TeV and will allow ATLAS and CMS to collect integrated luminosities of the order of 300 fb$^{-1}$ per year, and up to 3000 fb$^{-1}$ during the HL-LHC projected lifetime of ten years. The large expected integrat…
The potential of the LHC for investigation of anomalous top quark interactions with gluon ($tug,tcg$) through the production of $tW$-channel of single top quark is studied. In the Standard Model, the single top quarks in the $tW$-channel mode are charge symmetric meaning that $σ(pp\to t+W^{-}) = σ(pp\to \bar{t}+W^{+})$. However, the presence of anomalous FCNC couplings leads to charge asymmetry. In this paper a method is proposed in which this charge asymmetry may be used to constrain anomalous FCNC couplings. The strength of resulting constraints is estimated for the LHC for the center of mas…
The observed flavor-changing neutral-current (FCNC) processes in the standard model (SM) arise from the loop diagrams involving the weak charged currents mediated by the $W$-gauge boson. Nevertheless, the top-quark FCNCs and lepton-flavor violating processes resulting from the same mechanism are highly suppressed. We investigate possible new physics effects that can enhance the suppressed FCNC processes, such as $t\to q(h,V)$ with $V=γ,Z,g$, $h\to \ell \ell'$, and $\ell\to \ell' γ$. To achieve the assumption that the induced-FCNCs are all from quantum loops, we consider the scotogenic mechanis…
In the littlest Higgs model with T-parity (LHT) the newly introduced mirror quarks have flavor-changing couplings with the Standard Model (SM) quarks and may enhance the flavor-changing neutral-current (FCNC) top quark interactions which are extremely suppressed in the SM. In this work we perform a comprehensive study for the contributions of these mirror fermions to various top quark FCNC decays and productions at the LHC, which includes the decays t-> c V (V=g, γ, Z), t -> cgg and the productions proceeding through the parton processes cg -> t, gg -> t c_bar, cg -> tg, cg -> tγand cg -> t Z.…
We present a calculation of soft-gluon corrections in FCNC top-quark production via anomalous $t$-$q$-$g$ couplings. The soft anomalous dimension matrix is explicitly calculated at one-loop accuracy. This calculation allows threshold resummation at next-to-leading-logarithm accuracy. We also derive expressions for the soft-gluon corrections at NLO and at NNLO.
We discuss possible signatures of the tree level FCNC, which results from the non-unitarity of CKM matrix. We first define the unitaity step-by-step, and possible test of the non-unitaity through the 4-value-KM parametrization. We, then, show how the phase angle of the unitary triangle would change in case of the vector-like down quark model. As another example of tree FCNC, we investigate the leptophobic $Z'$ model and its application to the recent $B_s$ mixing measurements.
We examine experimental constraints on scharm-stop flavor mixing in the minimal supersymmetric standard model, which arise from the experimental bounds on squark and Higgs boson masses, the precision measurements of W-boson mass and the effective weak mixing angle, as well as the experimental data on B_s-\bar B_s mixing and b -> s gamma. We find that the combined analysis can put rather stringent constraints on \tilde{c}_L-\tilde{t}_L and \tilde{c}_L-\tilde{t}_R mixings. As an illustration for the effects of such constraints, we examine various top-quark flavor-changing neutral-current process…
A study of the top quark interactions via flavour-changing neutral current (FCNC) processes provides an intriguing connection between the heaviest elementary particle of the standard model (SM) of particle physics and the new scalar bosons that are predicted in several notable SM extensions. The production cross sections of the processes with top-scalar FCNC interactions can be significantly enhanced to the observable level at the CERN Large Hadron Collider. The present review summarizes the latest experimental results on the study of the top quark interactions with the Higgs boson via FCNC an…
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 discuss an extended standard model electroweak sector which contains a stable scalar dark matter particle, the D boson. To search for the D boson at the LHC we exploit the flavor-changing neutral current (FCNC) top quark decay, t->c D D, mediated by the lightest standard model-like Higgs h^0 in a two Higgs doublet model framework. The branching ratio for t->c D D in this case can be as high as 10^{-3}, after taking into account constraints arising from the D boson relic abundance. With an integrated luminosity of 10 (100) fb^{-1}, the 14 TeV LHC can explore values of this branching ratio th…
Large top quark flavor changing through neutral currents is expected by many extensions of the standard model. Direct and indirect searches for flavor changing neutral currents (FCNC) in the top quark decays to an up type quark (up,charm) and a Higgs boson are presented. We probe the observability of the top-Higgs FCNC couplings through the process e$^-$e$^+ \rightarrow t (\rightarrow \ell ν_{\ell} b) \,\, \bar{t} (\rightarrow q H)$, where $\ell$ = e, $μ$ and $q$ reflects up and charm quarks. It is shown that the branching ratio $Br(t\rightarrow qH)$ can be probed down to $1.12\times 10^{-3}$ …
We evaluate the $t\bar{c}$ and $t\bar{u}$ productions at the LHC within the general unconstrained MSSM framework. We find that these single top quark productions induced by SUSY-QCD FCNC couplings have remarkable cross sections for favorable parameter values allowed by current low energy data, which can be as large as a few pb. Once large rates of the $t\bar{c}$ and $t\bar{u}$ productions are detected at the LHC, they may be induced by SUSY FCNC couplings. We show that the precise measurement of single top quark production cross sections at the LHC is a powerful probe for the details of the SU…
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 one-loop contributions of the effective flavor changing neutral couplings (FCNC) tcZ and tcH on the electroweak precision observables Gamma_Z, R_c, R_b, R_l, A_c and A^FB_c. Using the known experimental limits on these observables, we may place 95% CL bounds on these FCNC couplings which in turn translate into the following limits for the branching ratios: BR(t -> cZ) < 6.7 10^-2 and BR(t -> cH) < (0.09 - 2.9) 10^-3 for 114 < m_H < 170 GeV.
We compute the partial width of the FCNC top quark decay t->c h in the framework of the Minimal Supersymmetric Standard Model, where h = h0, H0, A0 is any of the neutral Higgs of the MSSM. We include the SUSY electroweak, Higgs, and SUSY-QCD contributions. Our results substantially improve previous estimations on the subject, and we find that there is a possibility that they can be measured at LHC.
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…
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 % $
We study the combined effects of both strong and electroweak dimension six effective operators on flavour changing top quark physics at the LHC. Analytic expressions for the cross sections and decay widths of several flavour changing processes will be presented, as well as an analysis of the feasibility of their observation at the LHC.
In this paper, we investigated the process $pp \to W^{-}hj$ induced by the top-Higgs flavor changing neutral current (FCNC) couplings at the LHC. We found that the cross section of $pp \to W^{-}hj$ mainly comes from the resonant process $pp\to W^{-}t\to W^{-}hq$ due to the anomalous $tqH$ couplings (where $q$ denotes up and charm quarks). We further studied the observability of the top-Higgs FCNC couplings through the process $pp \to W^{-}(\to \ell^{-} \barν_{\ell}) h( \to γγ) j$ and found that the branching ratios $Br(t\to qh)$ can be probed to $0.16\%$ at $3σ$ level at 14 TeV LHC with an int…
We demonstrate how residual flavour symmetries, infrared signatures of symmetry breaking in complete models of flavour, can naturally forbid (or limit in a flavour specific way) flavour-changing neutral currents (FCNC) in multi-Higgs-doublet models (MHDM) without using mass hierarchies. We first review how this model-independent mechanism can control the fermionic mixing patterns of the Standard Model, and then implement the symmetries in the Yukawa sector of MHDM, which allows us to intimately connect the predictivity of a given flavour model with its ability to sequester FCNC. Finally, after…
We present a generator for single top quark production via flavour-changing neutral currents. The MEtop event generator allows for Next-to-Leading-Order direct top production $pp \to t$ and Leading-Order production of several other single top processes. A few packages with definite sets of dimension six operators are available. We discuss how to improve the bounds on the effective operators and how well new physics can be probed with each set of independent dimension six operators.
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…
