The one-loop contributions to the chromomagnetic dipole moment $\hatμ_t(q^2)$ and electric dipole moment $\hat d_t(q^2)$ of the top quark are calculated within the reduced 331 model (RM331) in the general case of an off-shell gluon. It is argued that the results are gauge independent for $q^2\ne 0$ and represent valid observable quantities. In the RM331 $\hat μ_t(q^2)$ receives new contributions from two heavy gauge bosons $Z'$ and $V^+$ and a new neutral scalar boson $h_2$, along with a new contribution from the standard model Higgs boson via flavor changing neutral currents. The latter, which are also mediated by the $Z'$ gauge boson and the scalar boson $h_2$, can give a non-vanishing $\hat d_t$ provided that there is a $CP$-violating phase. The analytical results are presented in terms of both Feynman parameter integrals and Passarino-Veltman scalar functions, which are useful to cross-check the numerical results. Both $\hatμ_t(q^2)$ and $\hat d_t$ are numerically evaluated for parameter values still allowed by the constraints from experimental data. It is found that the new one-loop contributions of the RM331 to $\hat μ_t(q^2)$ are of the same order of magnitude or larger than in other standard model extensions, with the dominant contribution arising from the $V^+$ gauge boson for $\|q\|$ in the 30-1000 GeV interval and a mass $m_{V}$ of the order of a few hundreds of GeVs. As for $\hat d_t(q^2)$, it receives the largest contribution from $h_2$ exchange and can reach values of the order of $10^{-20}$, which is smaller than the contributions predicted by other standard model extensions.
In this work we study the anomalous top quark-gluon couplings Chromoelectric Dipole Moment (CEDM) and Chromomagnetic Dipole Moment (CMDM) in a general THDM with CP violation. We find that this model provides an important contribution from the $Y_{tt}$ Yukawa coupling that needs to be taken into account. The CMDM and CEDM obtained are $-0.03<Δ\tilde{k} < 0.005}$ and $|Δ\tilde{d}| < 0.005$, respectively.
We study the effects of chromoelectric and chromomagnetic dipole moments (CEDM and CMDM) on the production cross section of single top $tW$-channel at the LHC based on the effective Lagrangian approach. We show that the impact of CEDM and CMDM could be large. Using the experimental measurement of the $tW$-channel cross section, constraints on CEDM and CMDM are extracted. These constraints are comparable with the ones obtained from the top pair analysis.
We study the effects of the anomalous chromoelectric and chromomagnetic dipole moments of the top quark on the top-pair production, on the top-pair plus 1jet production, and on their ratios, as well as their dependence on the transverse momenta of the top quark and the jet. We also construct CP-odd and $\hat T$-odd observables to probe the dispersive part of the chromoelectric form factor of the top quark, and compare their sensitivities in both top-pair and top-pair plus 1 jet production.
We propose an effective theory of SU(3) gluonic matter where interactions between color-electric and color-magnetic gluons are constrained by the center and scale symmetries. Through matching to the dimensionally-reduced magnetic theories, the magnetic gluon condensate qualitatively changes its thermal behavior above the critical temperature. We argue its phenomenological consequences for the thermodynamics, in particular the dynamical breaking of scale invariance.
Bounds on the absorptive (imaginary) parts of the top quark chromomagnetic $\hatμ_t$ and chromoelectric $\hat{d}_t$ dipole moments are obtained by reinterpreting the most recent LHC data in top quark pair production. It is found that both limits are of the order of $10^{-1}-10^{-2}$, which are consistent with the standard model prediction of ${\rm Im}\big[\hatμ_t\big]$. The effects of the absorptive parts of the top quark dipole moments are also studied via some kinematic distributions of $\bar{t}t$ production, though no significant deviation from the standard model leading order contribution …
In this paper we show that the $γ+$jet invariant mass distribution in proton-proton collisions at the LHC is significantly sensitive to the quarks chromoelectric ($κ$) and chromomagnetic ($\tildeκ$) dipole moments. It is shown that the presence of $κ$ or $\tildeκ$ leads to an increment of the cross section of $γ+$jet process in particular in the tail of $γ+$jet invariant mass distribution. Using the measured $γ+$jet invariant mass distribution by the CMS experiment at the center-of-mass energy of 8 TeV, we derive bounds on the quarks chromoelectric and chromomagnetic dipole moments. In extract…
The production of top quark pairs in association with a hard gluon in $e^+e^-$ collisions at the NLC provides an opportunity to probe for anomalous $t\bar tg$ couplings, \eg, the chromoelectric and chromomagnetic moments of the top. We demonstrate that an examination of the energy spectrum of the additional gluon jet can yield strong constraints on the size of these two anomalous couplings. The results are shown to be quite sensitive to the cut on the minimum gluon jet energy needed to remove events where the final state $b$-quark radiates strongly. The possibility of using additional observab…
The Tevatron, where the top quark was discovered, and the currently functional Large Hadron Collider (LHC), with copiously produced top pairs, enable a detailed study of top-quark properties. In particular, they can be used to test the couplings of the top quark to gauge bosons. Several extensions of the standard model (SM) can give rise to anomalous couplings of the top quark to gauge bosons, in particular, the gluons. In this work we examine how top-quark polarization, which is predicted to be negligibly small in the SM, can be used to measure chromomagnetic and chromoelectric couplings of t…
The heavy quark diffusion coefficient is encoded in the spectral functions of the chromoelectric and the chromomagnetic correlators that are calculable on the lattice. We study the chromoelectric and the chromomagnetic correlator in the deconfined phase of SU(3) gauge theory using Symanzik flow at two temperatures $1.5T_c$ and $10000 T_c$, with $T_c$ being the phase transition temperature. To control the lattice discretization errors and perform the continuum limit we use several temporal lattice extents $N_t=16,20,24$ and 28. We observe that the flow time dependence of the chromomagnetic corr…
We study the sensitivity of the Large Hadron Collider (LHC) to top quark chromomagnetic (CMDM) and chromoelectric (CEDM) dipole moments and $Wtb$ effective couplings in single-top production in association with a $W^-$ boson, followed by semileptonic decay of the top. We calculate the top polarization and the effects of these anomalous couplings on it at two centre-of-mass (cm) energies, 8 TeV and 14 TeV. As a measure of top polarization, we look at decay-lepton angular distributions in the laboratory frame, without requiring reconstruction of the rest frame of the top, and study the effect of…
We study the sensitivity of the Large Hadron Collider (LHC) to top quark chromomagnetic (CMDM) and chromoelectric (CEDM) dipole moments and $Wtb$ effective couplings in single-top production in association with a $W^-$ boson, followed by semileptonic decay of the top. The $Wt$ single-top production mode helps to isolate the anomalous $ttg$ and $Wtb$ couplings, in contrast to top-pair production and other single-top production modes, where other new-physics effects can also contribute. We calculate the top polarization and the effects of these anomalous couplings on it at two centre-of-mass (cm…
The effect of anomalous chromomagnetic (mu) and chromoelectric couplings (d) of the gluon to the top quark are considered in e+ e- --> t tbar, with unpolarized and longitudinally polarized electron beams. The total cross section, as well as t and tbar polarizations are calculated to order alpha_s in the presence of the anomalous couplings. One of the two linear combinations of t and tbar polarizations is CP even, while the other is CP odd. The limits that could be obtained at a typical future linear collider with an integrated luminosity of 50 1/fb and a total c.m. energy of 500 GeV on the mos…
The chromo magnetic dipole moment (CMDM) and chromo electric dipole moment (CEDM) of the top quark are calculated at the one-loop level in the framework of the two-Higgs doublet model with four fermion generations (4GTHDM), which is still consistent with experimental data and apart from new scalar bosons ($H^0$, $A^0$, and $H^\pm$) and quarks ($b'$ and $t'$) predicts new sources of $CP$ violation via the extended $4\times 4$ CKM matrix. Analytical expressions for the CMDM and CEDM of a quark are presented both in terms of Feynman parameter integrals and Passarino-Veltman scalar functions, with…
Using the CLEO data for $b\to sγ$, we constrain the chromomagnetic dipole moment of the top quark within the context of a decoupling effective Lagrangian approach. Our results are in agreement with the results obtained for the $e^+e^-$ and hadron colliders.
We calculate the virtual and bremsstrahlung fermionic corrections due to the interference of the electro- and chromomagnetic dipole operators in the inclusive \bar{B}\to X_sγdecay at O(α_s^2) and present analytical results for both the total decay rate and the photon energy spectrum.
A recently proposed Non-Standard Model solution to the problem of low semileptonic branching ratio B_{SL} which suggests a large branching ratio for the decay $b \to sg$ is critically examined. It is shown that the effects of the Enhanced Chromomagnetic Dipole Operator might lead to significant violations of isospin symmetry in rare radiative decays of B-mesons.
We present predictions at NLO accuracy in QCD for top-quark pair production induced by an anomalous chromomagnetic dipole moment of the top quark. Our results are obtained for total as well as fully differential cross sections, including matching to parton shower simulations. This process is expected to provide the most stringent direct limits on top-quark chromomagnetic dipole moment. We find that NLO corrections increase the contribution from the dipole moment by about 50\% at the LHC, and significantly reduce the renormalization and factorization scale dependence. Using the NLO prediction, …
The littlest Higgs model with T-parity, which is called $LHT$ model, predicts the existence of the new particles, such as heavy top quark, heavy gauge bosons, and mirror fermions. We calculate the one-loop contributions of these new particles to the top quark chromomagnetic dipole moment $(CMDM)$ $ΔK$. We find that the contribution of the $LHT$ model is one order of magnitude smaller than the standard model prediction value.
We give explicit formulae for the anomalous chromomagnetic dipole moment of the top quark in the framework of the standard model, the two higgs doublet model and the minimal supersymmetric standard model. Finally, we compare the results for this coupling with the bound -0.03 <= Delta kappa <= 0.01 coming from analysis of b --> s gamma process whith an on-shell gluon.
We calculate the chromomagnetic dipole moment of the top quark, $\hatμ_t$, in the context of the Bestest Little Higgs model. This extension of the Standard Model aims to solve the hierarchy problem without fine tuning, by introducing one-loop corrections to the Higgs boson mass through heavy top quark partners and heavy gauge bosons. We found that the largest resulting value for the chromomagnetic is $\hatμ_t\sim 10^{-5}$ and the lowest is around $10^{-6}$, mainly due to the Higgs boson of the Standard Model, which couples to both the top quark of the Standard Model and its heavy partners. Als…
We study the complete one-loop contributions to the chromagnetic dipole moment $Δκ$ of the top quark in the Standard Model, two Higgs doublet models, topcolor assited technicolor models (TC2), 331 models and extended models with a single extra dimension. We find that the SM predicts $Δκ= - 0.056$ and that the predictions of the other models are also consitent with the constraints imposed on $Δκ$ by low-energy precision measurements.
We calculate the one loop corrections to the chromomagnetic dipole moment of the top quark in the framework of the Standard Model, the two Higgs doublet model and the Minimal Supersymmetric Standard Model. In the Standard Model we consider the QCD and the electroweak corrections generated by gluon and Higgs boson exchanges, respectively. In the Minimal Supersymmetric Standard Model, we calculate the SUSY- QCD corrections, including the mixing effects between the stop coming from the left- and right-handed sectors. We obtain that the Standard Model contribution is of the order of -0.004< delta …
The anomalous chromomagnetic moment of the top quark arises from one loop corrections to the vertex $\bar t t g$. We give explicit formulae for this anomalous coupling in the framework of the standard model, the two Higgs doublet model and the minimal supersymmetric standard model. We compare the results for the anomalous coupling with the bound $-0.03 \leq Δκ\leq 0.01$ emerging from the analysis of $b \to s γ$ process with an on-shell bremsstrahlung gluon. This enables us to study the allowed region of parameters of the models under consideration.
We consider the possibility of having a large branching ratio for the decay $b\to s g$ coming from an enhanced Wilson coefficient of the chromomagnetic dipole operator. We show that values of $BR(b\to s g)$ up to $\sim 10\%$ or more are compatible with the constraints coming from the CLEO experimental results on $BR(B\to X_sγ)$ and $BR(B\to X_sϕ)$. Such large values can reconcile the predictions of both the semileptonic branching ratio and the charm counting with the present experimental results. We also discuss a supersymmetric model with gluino-mediated flavour violations, which can account …
Chromomagnetic and chromoelectric dipole interactions of the top quark are studied in a model independent framework. Limits are set on the scale of new physics that might lead to such contributions using available Tevatron data. Prospects at the LHC are reviewed.
We revisit the anomalous chromomagnetic dipole moment in the Standard Model and show that its triple gluon vertex contribution, with the on-shell gluon ($q^2=0$), generates an infrared divergent pole. Consequently, the chromomagnetic dipole should not be perturbatively evaluated at $q^2=0$. Focusing on this top quark anomaly, denoted as $\hatμ_t(q^2)$, we compute it with the off-shell gluon with a large momentum transfer, just as the $α_s(m_Z^2)$ convention scale, for both spacelike $q^2=-m_Z^2$ and timelike $q^2=m_Z^2$ cases. We found that $\hatμ_t(-m_Z^2)$ $=$ $-0.0224$ $-0.000925i$ and $\ha…
Anomalous chromomagnetic and chromoelectric dipole moments of the top quark may arise from various high scale theories. We carry out a model independent study of such interactions focusing on the limits that can be obtained from current Tevatron data and the improvements that may be possible at the LHC or at a future Linear Collider.
We present a complete analysis of the electric dipole moment (EDM) of the ρ-meson induced by CP violating operators of dimension 4 and 5 within the QCD sum rules approach. The set of CP-odd operators includes the theta term and the electric and chromoelectric dipole moments of the three light quarks. We find that the ρ-meson EDM induced purely by the EDMs of quarks is smaller, but still in reasonable agreement, with the predictions of a naive constituent quark model. However, the chromoelectric dipole moments, including that of the strange quark, give comparable and sometimes larger contributi…
A characteristic signature of quark confinement is the concentration of the chromoelectric field between a static quark-antiquark pair in a flux tube. However, the structure of this flux tube, and hence of the confining force, has not been completely understood. Here we perform new lattice measurements of field distributions on smeared Monte Carlo ensembles in SU(3) gauge theory. On the basis of these simulations we demonstrate that the confining force can be understood using the analogy with the basic principles of electromagnetism as elucidated by Maxwell. We derive a chromomagnetic Lorentz …
Using QCD sum rules, we calculate the electric dipole moment of the neutron d_n induced by all CP violating operators up to dimension five. We find that the chromoelectric dipole moments of quarks \tilde d_i, including that of the strange quark, provide significant contributions comparable in magnitude to those induced by the quark electric dipole moments d_i. When the theta term is removed via the Peccei-Quinn symmetry, the strange quark contribution is also suppressed and d_n =(1\pm 0.5)[1.1e(\tilde d_d + 0.5\tilde d_u)+1.4(d_d-0.25d_u)].
A complete one loop analysis of the chromoelectric dipole contribution to the electric dipole moment (edm) of the quarks and of the neutron in N=1 supergravity including the gluino, chargino and neutralino exchange contributions and exhibiting the dependence on the two CP violating phases allowed in the soft SUSY breaking sector of minimal supergravity models is given. It is found that in significant parts of the supergravity parameter space the chromoelectric dipole contribution to the neutron edm is comparable to the contribution from the electric dipole term and can exceed the contribution …
The connection between a regularization-independent symmetric momentum substraction (RI-$\tilde{\rm S}$MOM) and the $\overline{\rm MS}$ scheme for the quark chromo EDM operators is discussed. A method for evaluating the neutron EDM from quark chromoEDM is described. A preliminary study of the signal in the matrix element using clover quarks on a highly improved staggered quark (HISQ) ensemble is shown.
A system of chromodynamic fields, which can be treated as classical, is generated at the earliest stage of relativistic heavy-ion collisions. Numerical simulations show that the system is unstable but the nature of the instability is not well understood. We study the problem systematically. In the first paper, we have performed a linear stability analysis of space-time uniform chromoelectric and chromomagnetic fields. There they have been considered the Abelian configurations of single-color potentials linearly depending on coordinates and nonAbelian ones where the fields are generated by the …
The chromoelectric dipole moment of the top quark is calculated in a model with a vector like multiplet which mixes with the third generation in an extension of the MSSM. Such mixings allow for new CP violating phases. Including these new CP phases, the chromoelectric dipole moment that generates an electric dipole of the top in this class of models is computed. The top chromoelectric dipole moment operator arises from loops involving the exchange of the W, the Z as well as from the exchange involving the charginos, the neutralinos, the gluino, and the vector like multiplet and their superpart…
It is shown that standard constituent quark models produce $(\bar c c qqq)$ hidden-charm pentaquarks, where $c$ denotes the charmed quark and $q$ a light quark, which lie below the lowest threshold for spontaneous dissociation and thus are stable in the limit where the internal $\bar c c$ annihilation is neglected. The binding is a cooperative effect of the chromoelectric and chromomagnetic components of the interaction, and it disappears in the static limit with a pure chromoelectric potential. Their wave function contains color sextet and color octet configurations for the subsystems and can…
The initial stage of a heavy ion collision is dominated by nonperturbatively strong chromoelectric and -magnetic fields. The spatial Wilson loop provides a gauge invariant observable to probe the dynamics of the longitudinal chromomagnetic field. We discuss recent results from a real time lattice calculation of the area-dependence of the expectation value of the spatial Wilson loop. We show that at relatively early times after the collision, a universal scaling as a function of the area emerges at large distances for very different initial conditions, with a nontrivial critical exponent. A sim…
We investigate the lower bounds of sfermion masses from the constraints of chromoelectric dipole moments (CEDMs) in the natural SUSY-type sfermion mass spectrum, in which stop mass $m_{\tilde t}$ is much smaller than the other sfermion masses $m_0$. The natural SUSY-type sfermion mass spectrum has been studied since the supersymmetric (SUSY) flavor-changing neutral currents (FCNC) are suppressed because of large sfermion masses of the first two generations, and the weak scale is stabilized because of the light stop. However, this type of sfermion mass spectrum is severely constrained by CEDM, …
We calculate the fermionic corrections to the photon-energy spectrum of Bbar -> X_sgamma which arise from the self-interference of the chromomagnetic dipole operator Q_8 at next-to-next-to-leading order by applying naive non-abelianization. The resulting O(beta_0 alpha_s^2) correction to the Bbar -> X_sgamma branching ratio amounts to a relative shift of +0.12% (+0.27%) for a photon-energy cut of 1.6 GeV (1.0 GeV). We also comment on the potential size of resummation and non-perturbative effects related to Q_8.
An analysis is given of the chromoelectric dipole moment of quarks and of the neutron in an MSSM extension where the matter sector contains an extra vectorlike generation of quarks and mirror quarks. The analysis includes contributions to the CEDM from the exchange of the $W$ and the $Z$ bosons, from the exchange of charginos and neutralinos and the gluino. Their contribution to the EDM of quarks is investigated. The interference between the MSSM sector and the new sector with vectorlike quarks is investigated. It is shown that inclusion of the vectorlike quarks can modify the quark EDMs in a …
This paper examines detection prospects and constraints on the chromomagnetic dipole operator for the bottom quark. This operator has a flavor, chirality and Lorentz structure that is distinct from other dimension six operators considered in Higgs coupling studies. Its non-standard Lorentz structure bolsters boosted $b \bar{b} h$ events, providing a rate independent signal of new physics. To date, we find this operator is unconstrained by $p p \rightarrow h + {\rm jets}$ and $pp \rightarrow \bar b b $ searches: for order-one couplings the permitted cutoff $Λ$ for this operator can be as low as…
A new estimate of the one loop contributions of the standard model to the chromomagnetic dipole moment (CMDM) $\hat μ_q(q^2)$ of quarks is presented with the aim to address a few disagreements arising in previous calculations. We consider the most general case with an off-shell gluon with transfer momentum $q^2$ and obtain analytical results in terms of Feynman parameter integrals and Passarino-Veltman scalar functions, which are then expressed in terms of closed form functions when possible. The calculation is done via a renormalizable linear $R_ξ$ gauge and the background field method, which…
We do a perturbative calculation of the anomalous chromomagnetic dipole moment of quarks at one-loop, also considering the effect of a small gauge-invariant mass of the gluon. We find partial agreement with a previous calculation, as well as a divergence. We explain these results by noting that perturbation theory is not valid at the energy scales where these calculations were done, and proceed to give the results at the $M_Z$ scale. We find significant variation, of the anomalous moment of the light quarks, as a function of gluon mass.
Possible anomalous couplings of the top-quark to on-shell photons and gluons are constrained by the recent results of the CLEO Collaboration on both inclusive and exclusive radiative $B$ decays. We find that the process \bsg\ can lead to reasonable bounds on both the anomalous electric and magnetic dipole moments of the top-quark, while essentially no limits are obtained on the corresponding chromoelectric and chromomagnetic moments, which enter the expression for the decay rate only through operator mixing.
We consider the QCD corrections to the electric dipole moment of the neutron in the Minimal Supersymmetric Standard Model. We provide a master formula for the Wilson coefficients at the low energy scale including for the first time the mixing between the electric and chromoelectric operators and correcting widely used previous LO estimates. We show that, because of the mixing between the electric and chromoelectric operators, the neutralino contribution is always strongly suppressed. We find that, in general, the effect of the QCD corrections is to reduce the amount of CP violation generated a…
We calculate the electric dipole form factor of the nucleon that arises as a low-energy manifestation of time-reversal violation in quark-gluon interactions of effective dimension 6: the quark electric and chromoelectric dipole moments, and the gluon chromoelectric dipole moment. We use the framework of two-flavor chiral perturbation theory to one loop.
The problem of two nonrelativistic chromoelectric and chromomagnetic charges in a Higgs vacuum is considered in classical field theory. An approximation of interaction potential is constructed on the basis of a numerical solution to the equations of gluostatics. The concept of a non-Abelian Abrikosov vortex is discussed. It is shown that the results of Ginzburg-Landau theory for the tension of a string between magnetic charges can be directly extended to the non-Abelian case.
Constraints on the non-standard top-gluon couplings composed of the chromomagnetic- and chromoelectric-dipole moments of the top quark are updated by combining the latest data of top-pair productions from the Tevatron, 7-TeV LHC, and 8-TeV LHC. We find that adding the recent 8-TeV data to the analysis is effective to get a stronger constraint on the chromoelectric-dipole moment than the one from the Tevatron and 7-TeV LHC alone. We also discuss how those constraints on the non-standard couplings could be further improved when 14-TeV LHC results become available in the near future.
