Yuichiro Kiyo, Dirk Seidel, Matthias Steinhauser
We compute the last missing piece of the two-loop ${\cal O}(αα_s)$ corrections to $γt \bar{t}$ vertex at the $t \bar{t}$ threshold due to the exchange of a $W$ boson and a gluon. This contribution constitutes a building block of the top quark threshold production cross section at electron positron colliders.
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Extended technicolor theories generate potentially large corrections to the $\Zbb$ vertex. These can be observed in current experiments at LEP.
Extended technicolor theories generate potentially large corrections to the $\Zbb$ vertex which can be observed in current experiments at LEP.
A slowly running technicolor coupling will affect the size of non-oblique corrections to the $Zb\bar b$ vertex from extended technicolor dynamics. We show that while ``walking technicolor'' reduces the magnitude of the corrections, they generally remain large enough to be seen at LEP.
In this paper, we present the exact calculations for the vertex $\bar{s}γb$ and $\bar{s} Z b$ in the unitary gauge. We found that (a) the divergent- and $μ$-dependent terms are left in the effective vertex function $Γ^γ_μ(p,k)$ for $b \to s γ$ transition even after we sum up the contributions from four related Feynman diagrams; (b) for an on-shell photon, such terms do not contribute et al; (c) for off-shell photon, these terms will be canceled when the contributions from both vertex $\bar{s}γb$ and $\bar{s} Z b$ are taken into account simultaneously, and therefore the finite and gauge indepen…
Three-loop vertex diagrams in HQET needed for sum rules for B^0 - \bar{B}^0 mixing are considered. They depend on two residual energies. An algorithm of reduction of these diagrams to master integrals has been constructed. All master integrals are calculated exactly in d dimensions; their epsilon expansions are also obtained.
It is shown that the longitudinal double spin asymmetry $A_{ll}$ in polarized diffractive $l p \to l p+Q \bar Q$ reaction depends strongly on the spin structure of quark-pomeron vertex. The SMC spin facilities may be one of the best place to perform such experiment.
Using effective field theory techniques we discuss the QCD corrections to the large-$m_t$ contributions to the process $Z\rightarrow b \bar b$. In particular we obtain the $\a$ correction to the non-universal $\log m_t$ contribution to the $Zb\bar b$ vertex.
We present a model--independent analysis of the $Z b \bar b$ vertex, with the aim of constraining contributions of new physics to the left- and right--handed couplings of the $b$. We find that the left--handed coupling of the $b$ is quite narrowly constrained by present data, but that the right--handed coupling is still largely unconstrained.
I stress the fact that a complete study of possible New Physics effects in the $Z \rightarrow b\bar{b}$ vertex requires a combined analysis of the ratio $R_b= Γ(Z \rightarrow b\bar{b})/ Γ(Z \rightarrow hadrons)$ and the longitudinally polarized forward backward asymmetry, $A_b$. This is illustrated with a number of models such as the two Higgs-doublet model, the MSSM, Technicolour and models with an extra $Z'$. The use of effective lagrangean techniques is briefly discussed.
LEP precision measurements of the $Zb\bar{b}$ vertex coupling are sufficiently accurate to see the non-oblique corrections from the heavy gauge boson responsible for the large top mass in standard extended tecnicolour models. If the ETC couplings are strong the techni-fermion condensate may be enhanced by several orders of magnitude allowing a top mass of order 150GeV to be obtained for large values of the ETC breaking scale sufficient to supress the ETC contribution to the $Zb{\bar b}$ vertex. In this letter we investigate the degree of fine tuning of the ETC coupling required in a realistic …
Triple gauge boson vertex, which is inherent to the model of a dynamical breaking of the electroweak symmetry, leads to an effective four-fermion interaction of quarks. Calculation of the effective coupling constant in the framework of the model results in agreement with recent information on enhancement of inclusive high E_T jet cross section at \sqrt{s} = 1.8 TeV. Thus this effect may be connected with triple gauge boson vertex with coupling constant λ\approx 0.7, which will clearly manifest itself at the soon forthcoming LEP II.
We calculate the $F/D$ ratios of spin 1/2 baryon vertex for both the non-relativistic quark model and the chiral soliton model with arbitrary number of color degrees of freedom $N_c$ and examine the results in terms of the consistency condition approach for the baryon vertices recently developed by Dashen, Jenkins and Manohar from the viewpoint of QCD. We show that the $1/N_c$ corrections have two different origins, i.e. one is from the baryon states or baryon wave functions and the other from the vertex operators. Although in the limit of $N_c \to \infty$ the $F/D$ tends to 1/3 in all models,…
As a first step towards the computation of the NLO corrections to the photon impact factor in the $γ^*γ^* \to γ^* γ^*$ scattering process, we calculate the one loop corrections to the coupling of the reggeized gluon to the $γ^*\to q\bar{q}$ vertex. We list the results for the Feynman diagrams which contribute: all loop integrations are carried out, and the results are presented in the helicity basis of photon, quark, and antiquark.
The light axial vector mesons can couple to $K^*\bar{K}+c.c.$ in an $S$ wave at the tree level. Due to the near-threshold $S$-wave interactions the couplings can be affected by the final state interactions. It is of peculiar interest that the pion exchange between $K^*\bar{K}+c.c.$ can go through a triangle diagram which is within the kinematics of the triangle singularity (TS). This mechanism will introduce energy dependence and a $D$-wave amplitude to the vertex couplings. Hence, it should be necessary to investigate the role played by the $K^*\bar{K}+c.c.$ threshold in order to have a bette…
The reactions e+e- -> t bar-c nu_e bar-nu_e, t bar-c e+ e- are very sensitive probes of the flavor-changing-scalar couplings which can occur in a model with one extra Higgs doublet. At the Next Linear Collider, with a center of mass energy of sqrt{s}=0.5--2 TeV, several hundreds and up to thousands of such events may be produced if the mass of the light neutral Higgs is a few hundred GeV. We also briefly comment on the decays t -> c W+ W-, t -> c Z Z. All of these reactions are severely suppressed in the Standard Model
We estimate the correction to the Zbb-bar vertex arising from the exchanges of the sideways extended technicolor (ETC) boson and the flavor-diagonal ETC boson in the multiscale walking technicolor model. The obtained result is too large to explain the present data. However, if we introduce a new self- interaction for the top quark to induce the top quark condensate serving as the origin of the large top quark mass, the corrected R_b=Gamma_b/Gamma_h can be consistent with the recent LEP data. The corresponding correction to R_c=Gamma_c/Gamma_h is shown to be negligibly small.
In this paper we calculate the corrections to zt\bar {t} couplings induced by non-commuting ETC interactions. The extra parameters \delgbl, s^2 and {1\over x} of non-commuting ETC models and the usual SM parameters will be be assumed to be determined from a global fit to the LEP 1 EW data. We find that in the heavy (light) case F^t_L is modified by at most 4% (2.8%) relative to its SM value provided \delrb < .0088. This implies that it will be very difficult to disentangle the ETC corrections from SM corrections to zt\bar {t} vertex or to probe the effects of non-commuting ETC on zt\bar {t} co…
We study the one-loop corrections to the $Zb\bar{b}$ vertex in extensions of the Standard Model with arbitrary numbers of scalar doublets, neutral scalar singlets, and charged scalar singlets. Starting with a general parameterization of theories with neutral and singly-charged scalar particles, we derive the conditions that, in a renormalizable model, must be obeyed by the couplings in order for the divergent contributions to cancel. Then, we show that those conditions are indeed obeyed by the models that we are interested in, and we write down the full finite expression for the vertex in thos…
We investigate the new contributions to the parameters $g_L$ and $g_R$ of the $Z b \bar b$ vertex in a multi-Higgs-doublet model (MHDM). We emphasize that those contributions generally worsen the fit of those parameters to the experimental data. We propose a solution to this problem, wherein $g_R$ has the opposite sign from the one predicted by the Standard Model; this solution, though, necessitates light scalars and large Yukawa couplings in the MHDM.
We consider the leading one-loop Yukawa-coupling corrections to the h^0 b b-bar coupling at O(m_t^2)in the MSSM in the decoupling limit. The decoupling behavior of the corrections from the various MSSM sectors is analyzed in the case of having some or all of the supersymmetric mass parameters and/or the CP-odd Higgs mass large as compared to the electroweak scale.
Next-to-leading order QCD corrections to the $γ^{*} \longrightarrow Q\bar{Q}-Reggeon$ vertex are calculated, where $Q\bar{Q}$ denotes a heavy quark pair $c\bar c$ or $b\bar b$. The heavy quark mass effects on the photon impact factor are found to be significant, and hence may influence the results of high energy photon-photon scattering and heavy quark pair leptoproduction. In our NLO calculation, similar to the massless case, the ultraviolate(UV) divergences are fully renormalized in the standard procedure, while the infrared (IR) divergences are regulated by the parameter $ε_{IR}$ in dimensi…
Hadron diffraction dissociation is considered in the dipole Pomeron model where the Pomeron is represented by a double pole in the J-plane. We find that unitarity is satisfied without decoupling of the triple Pomeron vertex. The reaction bar{p}+p --> bar{p}+X is analysed.
We explore corrections to electroweak parameters in the context of Extended Technicolor (ETC) models in which the ETC gauge-boson which generates the top-quark mass carries weak $SU(2)$ charge. For $m_t \sim 150$ GeV there exist potentially large corrections to the $Z$ decay width to $b$-quarks. Interestingly, in contrast to the situation in ETC models where the gauge-boson which generates the top-quark mass is a weak $SU(2)$ singlet, the corrections may {\it increase} the $Z \to b \bar{b}$ branching ratio.
Motivated by $-2 σ$ deviation from the Standard Model prediction for the forward--backward asymmetry of $Z \to b \bar{b}$ decay in the LEP data, we explore the anomalous couplings of $Z b \bar{b}$ vertex through the electroweak precision test extended by including $A_{FB}^b$. We introduce a new variable $ε'_b$ to measure the anomalous right-handed coupling in $Z b \bar{b}$ vertex. Implications of our analysis on the nonuniversal contact interactions are studied and the left-right model is also considered as a possible origin of the anomalous right-handed couplings.
We calculate the corrections to the three-gluon decay widths $Γ_{3g}$ of $c\bar c$ and $b \bar b$ quarkonia due to the finite extension of the $Q\bar Q\to 3g$ vertex function. The widths computed with zero range vertex are reduced by a factor $γ$ where $γ=0.31$ for the $J/ψ$ and $γ=0.69$ for the $Υ$. These large corrections necessitate a redetermination of the values $α_s(μ)$ extracted from $Γ_{3g}$. We find $α_s(m_c)=0.28\pm.01$ and $α_s(m_b)=0.20\pm.01$.
The nonperturbative mechanism of baryon-antibaryon production due to double quark pair $(q\bar q)$($q\bar q)$ generation inside a hadron is considered and the amplitude is calculated as matrix element of the vertex operator between initial and final hadron wave functions. The vertex operator is expressed solely in terms of first principle input: current quark masses, string tension $σ$ and $α_s$. In contrast to meson-meson production via single pair generation, in baryon case a new entity appears in the vertex: the vacuum correlation length $λ$, which was computed before through string tension…
We extend our previous work on the precision electroweak tests in the Sp(6)_L X U(1)_Y family model to include for the first time the important Z->b b-bar vertex corrections encoded in a new variable epsilon_b, utilizing all the latest LEP data. We include in our analysis the one loop EW radiative corrections due to the new bosons in terms of epsilon_1, epsilon_b and $ΔΓ_Z$. We find that the correlation between epsilon_1 and epsilon_b makes the combined constraint much stronger than the individual ones. The model is consistent with the recent CDF result of $m_t=174\pm 10^{+13}_{-12}\GeV$, but …
The $Z b \bar b$ vertex in a left-right model
本文研究了左右手模型中 $Z b \bar b$ 顶点的单圈修正，发现该模型在拟合该顶点时并不优于标准模型的多希格斯扩展，两者均需引入极低质量标量粒子才能实现较好拟合。
We discuss the effects of isospin breaking which appear in the vertex corrections for $Zb \bar{b}$, $Zτ^+τ^-$ and $Wντ$ in a one-family technicolor model without exact custodial symmetry. By means of the effective lagrangian approach we compute the vertex corrections for $Zb\bar{b}$, $Zττ$ and $Wτν$ taking account of the contributions from technivectormesons. If the isospin symmetry in technilepton sector is not exact, technivectormesons contribute to the vertex correction for $Zττ$ but such contributions to the correction for $Wτν$ are absent. If the difference is measured, it is the evidence…
We establish the most general parametrization of the new physics tested by present precision measurements and possibly responsible for any deviation of the $Z\to b \bar b $ amplitude from its Standard Model result, under the assumption that it is CP symmetric and is induced by degrees of freedom which are too heavy to be ~directly produced at the future Colliders. This is achieved by writing the complete list of the $SU(3)_c\times SU(2) \times U(1) $ gauge invariant and CP symmetric $dim=6$ operators, involving only quarks of the third family and/or bosons. The quark ~containing operators are …
We explore the radiative corrections to the process $Z \to b \bar b$ in models with extended Higgs sectors. The observables $R_b = Γ(Z \to b \bar b)/Γ(Z \to \rm{hadrons})$ and the $Z b \bar b$ coupling asymmetry, $A_b = (g_L^2 - g_R^2)/(g_L^2 + g_R^2)$, are sensitive to these corrections. We present general formulae for the one-loop corrections to $R_b$ and $A_b$ in an arbitrary extended Higgs sector, and derive explicit results for a number of specific models. We find that in models containing only doublets, singlets, or larger multiplets constrained by a custodial $SU(2)_{c}$ symmetry so tha…
We analyze the supersymmetric (SUSY) QCD contribution to the $h^0 b \bar{b}$ coupling at one loop in the Minimal Supersymmetric Model (MSSM) in the decoupling limit. Analytic expressions in the large SUSY mass region are derived and the decoupling behavior of the corrections is examined in various limiting cases, where some or all of the SUSY mass parameters become large. We show that in the decoupling limit of large SUSY mass parameters and large CP-odd Higgs mass, the $h^0 b \bar b$ coupling approaches its Standard Model value at one loop. However, the onset of decoupling is delayed when $\t…
We explore the radiative corrections to the process Z --> b b-bar in models with extended Higgs sectors. The observables R_b (the Z hadronic branching fraction to b b-bar) and the b-quark asymmetry A_b = (g_L^2 - g_R^2)/(g_L^2 + g_R^2) are sensitive to these corrections. We find that in models containing only Higgs doublets, singlets, or larger multiplets constrained by a custodial SU(2) symmetry, the radiative corrections to R_b involving charged Higgs bosons always worsen the Standard Model fit to electroweak data. Thus, the present R_b data can be used to set lower bounds on the charged Hig…
We compute the four-loop corrections to the Higgs-bottom vertex within massless QCD and present analytic results for all color structures. The infrared poles of the renormalized form factor agree with the predicted four-loop pattern. Furthermore, we use the results for the Higgs-bottom, photon-quark, and Higgs-gluon form factors to provide hard matching coefficients in soft-collinear effective theory up to four-loop accuracy.
We calculate the $\mathcal{O}(α_s)$ QCD corrections to the inclusive $h\to b\bar b$ decay rate in the dimension-6 Standard Model Effective Field Theory (SMEFT). The QCD corrections multiplying the dimension-6 Wilson coefficients which alter the $hb\bar b$-vertex at tree-level are proportional to the Standard Model (SM) ones, so next-to-leading order results can be obtained through a simple rescaling of the tree-level decay rate. On the other hand, contributions from the operators $Q_{bG}$ and $Q_{HG}$, which alter the $gb\bar b$-vertex and introduce a $hgg$-vertex respectively, enter at $\math…
The $Z^0 \to b\bar b$ width, $Γ_b$, is analysed in conjunction with the total and hadronic $Z^0$ widths, $Γ_T$ and $Γ_h$. Assuming, tentatively, that the present 2$σ$ discrepancy in $Γ_b$ will substantiate as time goes on, for large values of $m_H$ it will be sufficient to modify the $Z^0 b \bar b$ vertex only. In contrast, for small values of $m_H$, the theoretical predictions for both the $Z^0$ width into light quarks and leptons as well as the $Z^0 \to b\bar b$ vertex will have to be modified.
The on-shell renormalization scheme for the electroweak theory is well studied in the standard model(SM), but a consistent on-shell renormalization scheme for the minimal supersymmetric standard model(MSSM) is still unknown. In MSSM, we study the on-shell scheme for three vertexes$Z\bar{l^I}l^I, W^+\bar{ν^I}l^I $ and $\tilde{L}^*_i\bar{χ^0_α}l^I$ with virtual SUSY particles (chargino, sneutrino, neutralino and slepton) at one-loop order. Instead of amplitude of a single triangle diagram, the sum of amplitude of triangle diagrams belonging to one suit can be renormalized in the on-shell scheme.…
A new method is proposed to search for the double beauty tetraquark $bb\bar{u}\bar{d}$ with a mass below the $BB$ threshold. The $b\bar{d}-\bar{b}d$ mixing can result in evolution of the tetraquark content to $b\bar{b}\bar{u}d$ with the following strong decay into the $Υ$(1S)$π^-$ and $Υ$(2S)$π^-$ final states in a secondary vertex displaced from the primary $pp$ collision vertex. This experimental signature is clean, has a high selection efficiency and can be well separated from backgrounds. Experimental signatures for searches for other double heavy tetraquarks are also discussed, suggesting…
Pion-mediated Cooper pairing of neutrons: beyond the bare vertex approximation
本文通过求解Dyson-Schwinger方程非微扰研究中子物质中π介子诱导的中子库珀配对，发现最低阶顶角修正显著改变密度-温度相变临界线，表明顶角修正不可忽略。
The differential equation method is applied to evaluate analytically two-loop vertex Feynman diagrams. Three on-shell infrared divergent planar two-loop diagrams with zero thresholds contributing to the processes Z --> bb bar (for zero b mass) and/or H --> gg are calculated in order to demonstrate a new application of this method.
We present a new, model independent method for extracting bounds for the anomalous $γWW$ couplings from hadron collider experiments. At the partonic level we introduce a set of three observables which are constructed from the unpolarized differential cross-section for the process $d\bar{u}\to W^{-}γ$ by appropriate convolution with a set of simple polynomials depending only on the center-of-mass angle. One of these observables allows for the direct determination of the anomalous coupling usually denoted by $Δκ$, without any simplifying assumptions, and without relying on the presence of a radi…
This brief note is devoted to a study of genuine non-perturbative corrections to the Landau gauge ghost-gluon vertex in terms of the non-vanishing dimension-two gluon condensate. We pay special attention to the kinematical limit which the bare vertex takes for its tree-level expression at any perturbative order, according to the well-known Taylor theorem. Based on our OPE analysis, we also present a simple model for the vertex, in acceptable agreement with lattice data.
Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the $e-τ$ mixing is much more constrained than the others, and the decays proportional to such vertex are usually very supressed. On the other hand, bounds on the quark sector are obtained from leptonic decays of the $B_{d,s}^{0}$ mesons and from $ΔM_{B_{d}^{0}}$. We emphasize that although the $B_{d}^{0}-\bar{B}_{d}^{0}$ mixing restricts severely the $% d-b$ mixing vertex, the upper bound for this vertex could still give a sizeable contri…
We propose a new method to extract $D^0-\bar{D}^0$ mixing parameters using the $D^0 \to \bar{K}{}^0 π^0$ decay with the $\bar{K}{}^0$ reconstructed in the semileptonic mode. Although a $K^0 \to π^\pm l^\mp ν_l$ decay suffers from low statistics and complexity of the secondary vertex reconstruction in comparison to the standard $K_{S} \to π^+ π^-$ vertex, it provides much richer, sometimes unique information about the initial state of a $K^0$-meson produced in a heavy-flavor hadron decay. In this paper it is shown that the reconstruction of the chain $D^0 \to K^0 (π^\pm l^\mp ν_l) π^0$ allows o…
In an effective theory containing only quark degrees of freedom, such as the extended Nambu-Jona-Lasinio model, the influence of the axial anomaly can be incorporated by a self-interaction of the 't Hooft determinant type. I will show that despite the theshold problem related to the eta-prime meson this leads to a significant suppression of the eta-prime coupling g_{η' q \bar{q}} to dynamical quarks which suggests a suppression of the eta-prime-NN vertex as compared to the eta-NN vertex.
A qqq BSE formalism based on an input 4-fermion Lagrangian of `current' u,d quarks, is employed for the construction of a relativistic qqq-wave function) via the BSE. Chiral invariance is ensured by the vector character of the gluonic propagator in the infrared regime, while the `constituent' masses are the low momentum limits of the dynamicalmass function generated by standard DBχ. The Covariant Instantaneity Ansatz (CIA) gives an exact 3D reduction of the BSE for baryon spectroscopy, while the reconstructed 4D form identifies the baryon quark vertex function reconstructed through a reversal …
The top quark chromomagnetic dipole moment in the SM from the 4-body vertex function
本文提出通过非阿贝尔四体顶点函数 $ggt\bar{t}$ 在单圈水平计算顶夸克反常色磁偶极矩，发现类空评估结果更接近实验值，优于三体顶点函数结果。
The leading heavy-top two-loop corrections to the \Zbb~vertex are determined from a direct evaluation of the corresponding Feynman diagrams in the large \Mt~limit. %The calculation is done in the naive %dimensional regularization scheme with anticommuting $\ga_5$. The leading one-loop top-mass effect is enhanced by $[1+\GF\Mt^2(9-π^2/3)/(8π^2\sqrt{2})]$. Our calculation confirms a recent result of Barbieri et al.
We construct the quark-antiquark scattering kernels of Bethe-Salpeter equation from the quark self-energy directly under two specific forms of quark-gluon vertices. The quark dressed tensor vertex is then calculated within this consistent framework and rainbow-ladder(RL) approximation. After employing a simplified nucleon model, the nucleon tensor charge can be defined with the tensor vertex. We then compute the tensor charge with the bare tensor vertex and the dressed vertices obtained in this framework and in RL approximation. The obtained results are consistent with the lattice QCD calculat…
We describe the formalism, and present the results, for a triple-Regge analysis of the available pp and p\bar{p} high-energy data which explicitly accounts for absorptive corrections. In particular, we allow for the gap survival probability, S^2, in single proton diffractive dissociation. Since for pp scattering the value of S^2 is rather small, the triple-Pomeron vertex obtained in this analysis is larger than that obtained in the old analyses where the suppression caused by the absorptive corrections was implicitly included in an effective vertex. We show that the bare triple-Pomeron couplin…
By differentiating the dressed quark propagator with respect to a variable background field, the linear response of the dressed quark propagator in the presence of the background field can be obtained. From this general method, using the vector background field as an illustration, we derive a general formula for the four-quark condensate $<{\tilde 0}|:{\bar q}(0)γ_μq(0){\bar q}(0)γ_μq(0):|{\tilde 0}>$. This formula contains the corresponding fully dressed vector vertex and it is shown that factorization for $<{\tilde 0}|:{\bar q}(0)γ_μq(0){\bar q}(0)γ_μq(0):| {\tilde 0}>$ holds only when the d…
The scattering of a baryon consisting of three massive quarks is investigated in the high energy limit of perturbative QCD. A model of a relativistic proton-like wave function, dependent on valence quark longitudinal and transverse momenta and on quark helicities, is proposed, and we derive the baryon impact factors for two, three and four t-channel gluons. We find that the baryonic impact factor can be written as a sum of three pieces: in the first one a subsystem consisting of two of the three quarks behaves very much like the quark-antiquark pair in gamma* scattering, whereas the third quar…
We propose a new model for naturally light Dirac neutrinos and explain the baryon asymmetry of the universe through neutrinogenesis. We extend the standard model with a real singlet scalar, a heavy singlet Dirac fermion and a heavy doublet scalar besides three right-handed neutrinos, respecting lepton number conservation and a Z_2 symmetry. The neutrinos acquire small Dirac masses due to the suppression of the weak scale over the heavy mass scale. As a key feature of our construction, once the heavy Dirac fermion and doublet scalar go out of equilibrium, their decays induce the CP asymmetry fr…
The recent CLEO results on on radiative $b$-quark decays are used to derive constraints on anomalous $WWγ$ couplings. These constraints are compared with expectations from $p\bar p\rightarrow e^\pm p\llap/_Tγ+X$ at the Tevatron. The usefulness of exclusive radiative $B$ meson decay channels in probing the $WWγ$ vertex is largely limited by present theoretical uncertainties in the calculation of hadronic matrix elements.
A general analysis of the n-vertex loop amplitude in a strong magnetic field is performed, based on the asymptotic form of the electron propagator in the field. As an example, the photon-neutrino processes are considered, where one vertex in the amplitude is of a general type, and the other vertices are of the vector type. It is shown, that for odd numbers of vertices only the SV_1 ... V_{n-1} amplitude grows linearly with the magnetic field strength, while for even numbers of vertices the linear growth takes place only in the amplitudes PV_1 ... V_{n-1}, VV_1 ... V_{n-1} and AV_1 ... V_{n-1}.…
Non-decoupling effects related to a large $m_t$ affecting non-oblique radiative corrections in vertices ($Z\bar{b}b$) and boxes ($B$-$\bar{B}$ mixing and $ε_K$) are very sensitive to the particular mechanism of spontaneous symmetry breaking. We analyze these corrections in the framework of a chiral electroweak standard model and find that there is only one operator in the effective lagrangian which modifies the longitudinal part of the $W^+$ boson without touching the oblique corrections. The inclusion of this operator affects the $Z\bar{b}b$ vertex, the $B$-$\bar{B}$ mixing and the CP-violati…
In this two part series a chiral confining model of baryons is used to describe low--lying negative parity resonances $N^*$, $Δ^*$, $Λ^*$ and $Σ^*$ in the mean field approximation. A physical baryon in this model consists of interacting valence quarks, mesons and a color and chiral singlet hybrid field coexisting inside a dynamically generated confining region. This first paper presents the quark contribution to the masses and wave functions of negative parity baryons calculated with an effective spin--isospin dependent instanton induced interaction. It does not include meson exchanges between…
We calculate the non-universal correction to the $Zb\bar{b}$ vertex in a simple extension of the Standard Model, where a charge $+2/3$ isosinglet quark is added to the standard spectrum. Comparison is made with other solutions to $R_b$ (and $R_c$) that demand particles lighter than $M_W$.
In this paper, we consider the electroweak production cross-section of a single anti-top-quark, a neutrino and a photon via charged current through the $e^-p \to e^-\bar b \to \bar t ν_e γ\to \bar t(\to W^- \to (qq', l^- \barν_l)+b) ν_eγ$ signal. Further, we derived the sensitivity expected to the magnetic dipole moment $(\hat a_V)$ and the electric dipole moment $(\hat a_A)$ of the top-quark at the Future Circular Collider Hadron Electron (FCC-he). We present our study for $\sqrt{s}=7.07, 10\hspace{0.8mm}TeV$, ${\cal L}=50, 100, 300, 500, 1000\hspace{0.8mm}fb^{-1}$, $δ_{sys}=0, 3, 5\hspace{0.…
In this proceeding we show the results found for the cross sections of the processes $\bar D D\toπX(3872)$, $\bar D^* D\to πX(3872)$ and $\bar D^* D^*\toπX(3872)$, information needed for calculations of the $X(3872)$ abundance in heavy ion collisions. Our formalism is based on the generation of $X(3872)$ from the interaction of the hadrons $\bar D^0 D^{*0} - \textrm{c.c}$, $D^- D^{*+} - \textrm{c.c}$ and $D^-_s D^{*+}_s - \textrm{c.c}$. The evaluation of the cross section associated with processes having $D^*$ meson(s) involves an anomalous vertex, $X\bar D^* D^*$, which we have determined by …
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