Many extensions of the Standard Model(SM) generate contributions to Flavor Changing Neutral Current(FCNC) processes that must have sufficient flavor suppression to be consistent with experiments, if the new physics (NP) is associated with a scale of a TeV. Here we present a mechanism for suppressing the NP effects to FCNC processes. We consider the possibility that the source of NP contributions to FCNC processes share the same flavor symmetry underlying the SM source of FCNC processes which are the quark and lepton mass matrices. We call this the principle of shared flavor symmetry. In the flavor symmetric limit, the quark and lepton mixing matrices have fixed forms and there are no NP FCNC processes. In the flavor symmetric limit, we take the quark mixing matrix to be the identity matrix and the lepton mixing matrix to be given by tri-bimaximal mixing. Realistic mixing matrices are obtained by the small breaking of the flavor symmetry. New contributions to FCNC processes arise because of non universal breaking of the flavor symmetry in the quark and lepton mass matrices and the NP sources of FCNC processes. In particular, we will focus on new FCNC effects that arise due to the breaking of flavor symmetry only in the quark and charged lepton mass matrices but not in the NP sector. In this scenario, NP contributions to FCNC processes is linked to the source of flavor symmetry breaking in the quark and charged lepton mass matrices. To demonstrate the mechanism we use a two higgs doublet model as an example of beyond the SM physics though one should be able to adapt this mechanism to other models of new physics.
We recently proposed a spontaneous A4 flavor symmetry breaking scheme implemented in a warped extra dimensional setup to explain the observed pattern of quark and lepton masses and mixings. The quark mixing is induced by bulk A4 flavons mediating "cross-brane" interactions and a "cross-talk" between the quark and neutrino sectors. In this work we explore the phenomenology of RS-A4 and systematically obtain bounds on the Kaluza-Klein (KK) mass scale implied by flavor changing neutral current (FCNC) processes. In particular, we study the constraints arising from Re(ε'/ε_K), b->sγ, the neutron ED…
I discuss a ``more minimal'' modification of the minimal supersymmetric standard model, in which supersymmetry breaking is connected with the physics of flavor. Flavor Changing Neutral Currents (FCNC) for the first two families are suppressed, and for the third family may be of comparable size to the FCNC in the Standard Model.
We propose an alternative method of constructing two Higgs-doublet models free from scalar mediated FCNC couplings at the tree-level. In a toy scenario, we have presented semi realistic textures for the Yukawa matrices, which can reproduce the approximate flavor structure in the quark sector. Presence of flavor diagonal but nonuniversal Yukawa couplings emerges as a distinguishing feature of such models.
We present SUSY_FLAVOR version 2.5 - program that calculates over 30 low-energy flavor observables in the general $R$-parity conserving MSSM. Comparing to previous versions, in SUSY_FLAVOR v2.5 parameter initialization in SLHA2 formats has been significantly generalized, so that the program accepts most of the output files produced by other libraries analyzing the MSSM phenomenology. Number of bugs and inconsistencies have been fixed, based on users feedback. Calculations of several processes implemented in earlier versions have been corrected. New processes of rare decays of the top quark to …
In the context of Supersymmetric Grand Unified theories with soft breaking terms arising at the Planck scale, it is generally possible to link flavor changing neutral current and CP violating processes occurring in the leptonic and hadronic sectors. We study the correlation between flavor changing squark and slepton mass insertions in models à la SU(5). We show that the constraints coming from lepton flavor violation exhibit a strong impact on CP-violating B decays.
We study the three body lepton flavor violating (LFV) decays $μ^- \to e^- e^+ e^-$, $τ^- \to l_i^- l_j^+ l_j^-$ and the semileptonic decay $τ\to μϕ$ in the flavor changing neutral current (FCNC) mediated $Z$ boson model. We also calculate the branching ratios for LFV leptonic B decays, $B_{d,s} \to μe$, $B_{d,s} \to τe$, $B_{d,s} \to τμ$ and the conversion of muon to electron in Ti nucleus. The new physics parameter space is constrained by using the experimental limits on $μ^- \to e^- e^+ e^-$ and $τ^- \to μ^- μ^+ μ^-$. We find that the branching ratios for $τ\to eee $ and $τ\to μϕ$ processes …
The top quark flavor changing neutral current (FCNC) process is an excellent probe to search for new physics in top sector since the Standard Model expectation is extremely suppressed. We explore Higgs-mediated top quark FCNC, focusing on $H$-$t$-$c$ Yukawa coupling $λ_{ct}$ within the general two Higgs doublet model. After electroweak symmetry breaking the top quark FCNC couplings are included in the charged Higgs Yukawa sector so that they contribute to various processes in flavor physics. To probe $λ_{ct}$, we study anomalous single top production and the same sign top pair production at th…
The LHC will have unprecedented sensitivity to flavor-changing neutral current (FCNC) top quark decays, whose observation would be a clear sign of physics beyond the standard model. Although many details of top flavor violation are model dependent, the standard model gauge symmetries relate top FCNCs to other processes, which are strongly constrained by existing data. We study these constraints in a model independent way, using a low energy effective theory from which the new physics is integrated out. We consider the most important operators which contribute to top FCNCs and analyze the curre…
We investigated a general framework of the Standard Model with two Higgs doublets (2HDSM) with suppressed flavor-changing neutral currents (FCNC's). Loop-induced FCNC (and CP-violating) effects, when confronted with experimental constraints for the $K$-$\bar K$, $B$-$\bar B$ and $D$-$\bar D$ mixing and for the $(b \to s γ)$ decay, provide us with constraints on the values of the dominant Yukawa couplings of the charged Higgs, i.e., the values of the couplings of $H^{\pm}$ to $t$ and $b$ quarks. Once these {\it low} energy experimental data relevant for the mixings and for the mentioned decay, …
We study phenomenological constraints on a simple $3-3-1$ model with flavor violating Yukawa couplings. Both triplets Higgs couple to leptons and quarks, which generates flavor violating signals in both lepton and quark sectors. We have shown that this model can allow for large Higgs lepton flavor-violating rate decay $h \rightarrow μτ$ and also can be reached to perfect agreements with other experimental constraints such as $τ\rightarrow μγ$ and $(g-2)_μ$. The contributions of flavor-changing neutral current (FCNC) couplings, Higgs-quark-quark couplings, to the mesons mixing are investigated.…
The Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix and flavor-changing neutral currents (FCNC's) in the quark sector are examined in the GUT inspired $SO(5) \times U(1) \times SU(3)$ gauge-Higgs unification in which the 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Gauge invariant brane interactions play an important role for the flavor mixing in the charged-current weak interactions. The CKM matrix is reproduced except that the up quark mass needs to be larger than the observed one. FCNC's are naturally suppressed as a consequence of the gauge invariance, wi…
The stability of the standard vacuum imposes constraints on flavor violating trilinear soft terms which are stronger than the laboratory bounds coming from the absence of neutral flavor violations (FCNC). Furthermore, contrary to the FCNC bounds, these constraints persist even if the scale of supersymmetry breaking is arbitrarily large.
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.
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…
A non-universal interaction associated with top quark induces flavor changing neutral currents (FCNC) among light fermions. The size of the FCNC effect depends crucially on the dynamics of the fermion mass generation. In this paper, we study the effect of a non-universal interaction on $Z b b$, $Z b s$ {\it etc}, by using an effective lagrangian technique and assuming the quark mass matrices in the form of a generalized Fritzsch ansatz. We point out that if fitting $R_b$ to the LEP data within $1 σ$, the induced FCNC couplings are very close to the experimental limits.
As a minimal theory of fermion masses we extend the SM by heavy vectorlike fermions, with flavor-anarchical Yukawa couplings, that mix with chiral fermions such that small SM Yukawa couplings arise from small mixing angles. This model can be regarded as an effective description of the fermionic sector of a large class of existing flavor models and thus might serve as a useful reference frame for a further understanding of flavor hierarchies in the SM. Already such a minimal framework gives rise to FCNC effects through exchange of massive SM bosons whose couplings to the light fermions get modi…
Constraints from flavour changing neutral currents are discussed in the context of predictive Grand Unified Supersymmetric Theories. Uncertainties in the estimation of their amplitudes are minimized by using a successful mass matrix ansatz which predicts the arbitrary parameters of the Standard Model. Furthermore, Renormalization Group Equations are used in order to express the sparticle masses involved, in terms of the gaugino mass $m_{1/2}$, the universal scalar mass $m_0$ and the trilinear coupling $A$ at the GUT scale. Modifications in the low energy expressions for the squark masses due t…
The most general two-Higgs doublet model (2HDM) includes potentially large sources of flavor changing neutral currents (FCNCs) that must be suppressed in order to achieve a phenomenologically viable model. The flavor alignment ansatz postulates that all Yukawa coupling matrices are diagonal when expressed in the basis of mass-eigenstate fermion fields, in which case tree-level Higgs mediated FCNCs are eliminated. In this work, we explore models with the flavor alignment condition imposed at a very high energy scale, which results in the generation of Higgs-mediated FCNCs via renormalization gr…
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…
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 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.
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…
We propose a E_6 inspired supersymmetric model with a non-Abelian discrete flavor symmetry; SU(3)_c x SU(2)_W x U(1)_Y x U(1)_X x S_4 x Z_2. In our scenario, the additional abelian gauge symmetry; U(1)_X, not only solves the mu-problem in the minimal Supersymmetric Standard Model(MSSM), but also requires new exotic fields which play an important role in solving flavor puzzles. If our exotic quarks can be embedded into a S_4 triplet, which corresponds to the number of the generation, one finds that dangerous proton decay can be well-suppressed. Hence, it might be expected that the generation st…
A mechanism for double suppression of flavor-changing neutral currents (FCNCs) and CP violating phases in supersymmetric models is suggested. At M_{SUSY} they are suppressed due to a nonabelian discrete flavor symmetry, and the infrared attractive force of gauge interactions in extra dimensions are used to suppress them at the compactification scale. We present a concrete model, which is a simple extension of S_{3} invariant minimal supersymmetric standard model, where only SU(2)_{L} and SU(3)_{C} gauge multiplets are assumed to propagate in the bulk. We find that a disorder of two orders of m…
We discuss the Flavor-Changing Neutral Current (FCNC) decays of the top quark t -> c Vi Vj (Vi=gamma, Z, g) in the framework of the Standard Model (SM) and in a two-higgs doublet model (2HDM) with tree-level FCNC couplings. While in the SM the expected branching ratios are extremelly small, in the 2HDM they may be sizable, of order 10^(-5) - 10^(-5), and thus accesible at the CERN LHC. We conclude with the interesting observation that the FCNC decay modes may not be equally suppressed as their corresponding decays t ->c Vi in this 2HDM.
Flavor changing neutral current and lepton flavor violating processes are studied in the SU(5) SUSY-GUT with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of $b \to s γ$ can be as large as 20%. We also show that the $B_s$-$\bar{B}_s$ mixing can be significantly different from the standard model prediction.
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.…
In this Thesis we have investigated some effects appearing in top quark and Higgs boson decays with flavor changing neutral currents (FCNC) in the framework of generic Two Higgs Doblet Models (2HDM) and the Minimal Supersymmetric Standard Model (MSSM). We have applied these two extensions to the SM to see whether they can produce new FCNC effects. Introductory chapters deal with the 2HDM and the MSSM. In the next chapters we have computed the following FCNC decays: (1) the branching ratios (B) of the top quark to Higgs bosons and charm quark in the 2HDM; (2) B and number of events at the Large…
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 compute and analyze the Flavor-Changing Neutral Current (FCNC) interactions of Minimal Supersymmetric Standard Model Higgs bosons (h = h0, H0, A0) with heavy quarks (top and bottom), focusing on the strongly-interacting sector. We correlate the Higgs bosons production cross-section at the LHC with the FCNC decay branching ratios and find the maximum allowed values of the production rates, sigma(pp -> h -> qq') = sigma(pp -> h) x B(h -> qq') (qq'= tc or bs) after taking into account limits from low energy data on flavor-changing interactions. We single out the top channel, with a maximum pro…
In the context of a warped extra-dimension with Standard Model fields in the bulk, we obtain the general flavor structure of the Higgs couplings to fermions. These couplings will be generically misaligned with respect to the fermion mass matrix, producing large and potentially dangerous flavor changing neutral currents (FCNC's). As recently pointed out in [arXiv:0906.1542], a similar effect is expected from the point of view of a composite Higgs sector, which corresponds to a 4D theory dual to the 5D setup by the AdS-CFT correspondence. We also point out that the effect is independent of the g…
We study the effect of including flavor changing neutral currents (FCNC) in the analysis of the neutrino signal of a supernova burst. When we include the effect of the FCNC which are beyond the standard model (SM) in the study of the MSW resonant conversion, we obtain dramatic changes in the Δm^2-sin^2(2θ) probability contours for neutrino detection.
In extra dimensions the infrared attractive force of gauge interactions is amplified. We find that this force can align in the infrared limit the soft-supersymmetry breaking terms out of their anarchical disorder at a fundamental scale, in such a way that flavor-changing neutral currents as well as dangerous CP-violating phases are sufficiently suppressed at the unification scale. The main assumption is that the matter and Higgs supermultiplets and the flavor-dependent interactions such as Yukawa interactions are stuck at the four-dimensional boundary. As a concrete example we consider the min…
Motivated by the rencent LHC data on the lepton-flavor violating (LFV) decays $h\to \ell_1 \ell_2$ and $B_{s,d}\to \ell_1 \ell_2$, we study the Higgs-mediated flavor-changing neutral current (FCNC) interactions in the effective field theory (EFT) approach without and with the minimal flavor violation (MFV) hypothesis, and concentrate on the later. After considering the $B$ and $K$ physics data, the various LFV processes, and the LHC Higgs data, severe constraints on the Higgs FCNC couplings are derived, which are dominated by the LHC Higgs data, the $B_s - \bar B_s$ mixing, and the $μ\to e γ$ …
It is well known that a non-universal $Z^\prime$ induces tree-level FCNC which are severely constrained by experiment, most notably meson mixing. We point out that there is a class of models, with a down-quark mass matrix of the Georgi-Jarlskog form, in which the FCNC in the down-type quark sector vanish or are strongly suppressed. The largest FCNC in these models would occur in the $tc$ transition with a strength comparable to $V_{ts}$.
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}…
A Peccei-Quinn~(PQ) symmetry is proposed in order to generate in the Standard Model~(SM) quark sector a realistic mass matrix ansatz with five texture-zeros. Limiting our analysis to Hermitian mass matrices, we show that this requires a minimum of 4 Higgs doublets. This model allows assigning values close to 1 for several Yukawa couplings, giving insight into the origin of the mass scales in the SM. Since the PQ charges are non-universal, the model features Flavor-Changing Neutral Currents~(FCNC) at the tree level. From the analytical expressions for the FCNC we report the allowed region in th…
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.
In the context of the 331 models, we consider constraints on the extra neutral boson $Z^{\prime}$ predicted by the model, where three different quark family assignments are identified. Using the ansatz of Matsuda as an specific texture for the quark mass matrices, we obtain allowed regions associated with the Z-Z' mixing angle, the mass of the $Z^{\prime}$ boson and the parameter $β$ which determines different 331 models. The $Z_{1}$ and $Z_{2}$ decays with and without flavor changing are also considered. The flavor changing decays of the $Z_{1}$ boson into quarks at tree level are highly supp…
We analyze the maximum branching ratios for the Flavor Changing Neutral Current (FCNC) decays of the neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) into bottom quarks, h -> b\bar{s} (h=h^0,H^0,A^0). We consistently correlate these decays with the radiative B-meson decays (b-> sγ). A full-fledged combined numerical analysis is performed of these high-energy and low-energy FCNC decay modes in the MSSM parameter space. Our calculation shows that the available data on B(b->s γ) severely restricts the allowed values of B(h->b\bar{s}). While the latter could reach a few per…
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 study the effect of both Z and Z'-mediated flavor-changing neutral currents (FCNCs) on the $ lambda_b arrow lambda l^+l^- (l = mu, tau) $ rare decay. We find the branching ratio is reasonably enhanced from its standard model value due to the effect of both Z and Z'-mediated FCNCs, and gives the possibility of new physics beyond the standard model. The contribution of Z'-boson depends upon the precise value of the mass of Z' boson.
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…
Decays of the top quark induced by flavor changing neutral currents (FCNC) are known to be extremely rare events within the Standard Model. This is so not only for the decay modes into gauge bosons, but most notably in the case of the Higgs channels, e.g. t-> H_{SM}+c, with a branching fraction of 10^{-13} at most. Therefore, detection of FCNC top quark decays in a future high-energy, and high-luminosity, machine like the LHC or the LC would be an indisputable signal of new physics. In this paper we show that within the simplest extension of the SM, namely the general two-Higgs-doublet model, …
The meaning of non-abelian super flavorsymmetry in the presence of Multiple Higgs Doublets is twofold: The first one is to order the Yukawa sector of the standard model, while generating the Cheng-Sher suppression of tree-level Flavor Changing Neutral Currents (FCNCs), and the second one is to soften the fine tuning problem in the scalar potential and at the same time to suppress FCNCs coming from the soft breaking of supersymmetry. If spontaneous CP violation is combined with non-abelian super flavorsymmetry the CP phases in the soft supersymmetry breaking sector can disappear. This feature o…
Single top quark production is a powerful process to search for new physics signs. In this work we propose and investigate a search for top quark flavor changing neutral currents (FCNC) via a photon using direct single top quark production events in proton-proton collisions at the LHC at CERN. We show that the direct single top quark final state can provide constraints on the strengths of tq$γ$ (top-quark-$γ$) and tqg (top-quark-gluon) FCNC couplings simultaneously. Results of a search for direct single top quark production at the LHC at a center-of-mass energy of 8 TeV performed by the ATLAS …
We propose the local $(B-L)_{μτ}$ model, which minimally retains the local $B-L$ extension for the sake of neutrino phenomenologies, and at the same time presents an invisible gauge boson $Z'$ with mass $\sim {\cal O}(10)$ MeV to account for the discrepancy of the muon anomalous magnetic moment. However such a scenario is challenged by flavor physics. To accommodate the correct pattern of Cabibbo-Kobayashi-Maskawa matrix, we have to introduce either a $SU(2)_L$ doublet flavon or vector-like quarks plus a singlet flavon. In either case $Z'$ induces flavor changing neutral current (FCNC) in the …
CP violating effects in the single top quark production via flavour changing neutral current (FCNC) reactions $e^+e^- ->t bar{q}$ and $e^+e^- ->bar{t}q$ (here $q$ refers to charm and up quarks) are studied. The effective Lagrangian description of the FCNC interactions is used. A numerical analysis is performed for some next linear colliders. CP violating asymmetries for the number of $q$ and $\bar{q}$ quarks are obtained to be of order $10^{-2}-10^{-3}$ depending on the CM energy.
Low-energy experiments involving kaon, B-meson, D-meson, and hyperon flavor-changing neutral transitions have confirmed the loop-induced flavor-changing neutral current (FCNC) picture of the standard model (SM). The continuing study of these processes is essential to further refine this picture and ultimately understand the flavor dynamics. In this paper we consider deviations from the SM in the charm sector and their effect on FCNC processes. Specifically, we parameterize new physics in terms of left- and right-handed anomalous couplings of the W boson to the charm quark. We present a compreh…
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 % $
Flavor changing neutral currents coming from a new non-universal neutral Gauge-Boson and from the non-unitary quark mixing matrix for the $SU(3)_c\otimes SU(3)_L\otimes U(1)_X$ model with right handed neutrinos are studied. By imposing as experimental constraints the measured values of the 3x3 quark mixing matrix, the neutral meson mixing, and the bounds measured values for direct flavor changing neutral current processes, the largest mixing of the known quarks with the exotic ones can be established, with new sources of flavor changing neutral currents being identified. Our main result is tha…
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.
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 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.
I review recent progress in theoretical calculations related to the CKM unitarity triangle. After briefly discussing hints for new physics in B_d-B_d-bar mixing and B_s-B_s-bar mixing I present three topics of MSSM flavor physics: First I discuss new tan-beta-enhanced radiative corrections to flavor-changing neutral current (FCNC) amplitudes which go beyond the familiar Higgs-mediated FCNC diagrams and may enhance the mixing-induced CP asymmetry in B_d -> phi K_S. The second topic is a reappraisal of the idea that flavor violation originates from the soft supersymmetry-breaking terms. Finally …
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…
Flavor-changing neutral currents (FCNC) are studied on the basis of a ``democratic seesa'' mass matrix model, which yields a singular enhancement of the top-quark mass m_t and can give reasonable quark masses and CKM matrix elements. The most exciting aspect of the model is that the structure of the $6 \times 6$ right-handed fermion mixing matrix in the up-quark sector, $U^R_u$, shows an abnormal structure in contrast to that of $U^L_u$. This causes characteristic effects on the right-handed FCNC concerned with top quark. A single top-quark production at future $e^+ e^-$ colliders, $e^+ + e^- …
In this paper we show that the diphoton mass spectrum in proton-proton collisions at the LHC is sensitive to the top quark flavor changing neutral current in the vertices of $tuγ$ and $tcγ$. The diphoton mass spectrum measured by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV and an integrated luminosity of 19.5 fb$^{-1}$ is used as an example to set limits on these FCNC couplings. It is also shown that the angular distribution of the diphotons is sensitive to anomalous $tuγ$ and $tcγ$ couplings and it is a powerful tool to probe any value of the branching fraction of top qu…
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…
