We review the anomalous Chromomagnetic Dipole Moment (CMDM) of the top quark in a Two Higgs Doublet Model (2HDM). We include interactions with the involvement of the extended CKM matrix in this model, we obtain new bonds for the future experimental measurements and theoretical considerations.
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.
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 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 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 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.
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 …
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 …
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…
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…
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.
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, whic…
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…
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…
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.
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…
The electromagnetic dipole moments of the tau lepton and the chromoelectromagnetic dipole moments of the top quark are estimated via flavor-changing neutral currents, mediated by a new neutral massive gauge boson. We predict them in the context of models beyond the Standard Model with extended current sectors, in which simple analytic expressions for the dipole moments are presented. For the different $Z^\prime$ gauge boson considered, the best prediction for the magnetic dipole moment of the tau lepton, $|a_τ|$, is of the order of $10^{-8}$, while the highest value for the electric one, $|d_τ…
We study the Electric Dipole moment of b quark in the general two Higgs Doublet model (model III) and three Higgs Doublet model with O(2) symmetry in the Higgs sector. We analyse the dependency of this quantity to the new phase coming from the complex Yukawa couplings and masses of charged and neutral Higgs bosons. We see that the Electric Dipole moment of b quark is at the order of 10^{-20} e cm, which is an extremely large value compared to one calculated in the SM and also two Higgs Doublet model (model II) with real Yukawa couplings.
We study the lepton electric dipole moments in the split fermion scenario, in the two Higgs doublet model, where the new Higgs scalars are localized around the origin in the extra dimension, with the help of the localizer field. We observe that the numerical value of the electron (muon, tau) electric dipole moment is at the order of the magnitude of 10^{-31} (10^{-24}, 10^{-22}) (e-cm) and this quantity is sensitive the new Higgs localization in the extra dimension.
We study the the effects of non-universal extra dimensions on the electric dipole moments of fermions in the two Higgs doublet model. We observe that the t quark and b quark electric dipole moments are sensitive to the extra dimensions, however, in the case of charged lepton electric dipole moments, this sensitivity is relatively weak.
We predict the charged lepton electric dipole moments in the split fermion scenario in the framework of the two Higgs doublet model. We observe that the numerical value of the muon (tau) electric dipole moment is at the order of the magnitude of $10^{-22} (e-cm)$ ($10^{-20} (e-cm)$) and there is an enhancement in the case of two extra dimensions, especially for the tau lepton electric dipole moment.
The electric and weak electric dipole form factors for heavy fermions are calculated in the context of the most general two-Higgs-doublet model (2HDM). We find that the large top mass can produce a significant enhancement of the electric dipole form factor in the case of the b and c quarks. This effect can be used to distinguish between different 2HDM scenarios.
We study the electric and chromo electric dipole moment of top quark in the general two Higgs Doublet model (model III). We analyse the dependency of this quantity to the new phases coming from the complex Yukawa couplings and masses of charged and neutral Higgs bosons. We observe that the electric and chromo elecric dipole moments of top quark are at the order of 10^{-21} e cm and 10^{-20} g_s cm, which are extremely large values compared to ones calculated in the SM and also two Higgs Doublet model with real Yukawa couplings.
We calculate the electric dipole moment of electron using the experimental result of muon electric dipole moment and upper limit of the BR(μ--> eγ) in the framework of the general two Higgs doublet model. Our prediction is 10^{-32} e-cm, which lies in the experimental current limits. Further, we obtain constraints for the Yukawa couplings \barξ^{D}_{N,τe} and \barξ^{D}_{N,τμ}. Finally we present an expression which connects the BR(τ\to μγ) and the electric dipole moment of τ-lepton and study the relation between these physical quantities.
We point out that the standard chromomagnetic penguin dipole operator has a counterpart corresponding to off-shell momenta for external quarks. By employing the chiral quark model, we show that this new dipole penguin operator has the same bosonisation as the standard Q_6 operator. Accordingly, this new operator enlarges by ~ 5 % the referent Q_6 contribution, which gives the dominant contribution to the CP-violating ratio epsilon'/epsilon and also gives an important contribution to the Delta I = 1/2 amplitude.
The effect of the "chromo-electric" dipole moment on the electric dipole moment(EDM) of the neutron is studied in the two-Higgs-doublet model. The Weinberg's operator $O_{3g}=GG\t G$ and the operator $O_{qg}=\bar qσ\t Gq$ are both investigated in the cases of $\tan\b\gg 1$, $\tan\b\ll 1$ and $\tan\b\simeq 1$. The neutron EDM is considerably reduced due to the destructive contribution with two light Higgs scalars exchanges.
In the framework of a two Higgs doublet model type I and type II, we calculate limits on neutrino masses for the different types of neutrinos, by using the experimental bounds on their magnetic dipole moments. This is carried out by analyzing diagrams of Cherenkov neutrino decays with a charged Higgs into the loop, coming from the two Higgs doublet model (2HDM). Such constraints are translated into allowed regions in the free parameters of the models, for each neutrino flavor. The analysis was performed by sweeping the charged Higgs mass between (100-900)GeV and taking into account the experim…
We study the electric dipole moments(EDM) of the neutron and the electron in the two-Higgs-doublet model, in the case that $CP$ symmetry is violated maximally in the neutral Higgs sector. We take account of the Weinberg's operator $O_{3g}=GG\t G$ as well as the operator $O_{qg}=\bar qσ\tilde Gq$ for the neutron, and the Barr-Zee diagrams for the electron. It is found that the predicted neutron EDM could be considerably reduced by the destructive contribution of the two Higgs scalars to get the lower value than the experimental bound. As to the electron EDM, the predicted value is smaller in on…
We study the effect of the "chromo-electric" dipole moment on the electric dipole moment(EDM) of the neutron in the two Higgs doublet model. We systematically investigate the Weinberg's operator $O_{3g}=GG\t G$ and the operator $O_{qg}=\bar qσ\t Gq$, in the cases of $\tan\b\gg 1$, $\tan\b\ll 1$ and $\tan\b\simeq 1$. It is shown that $O_{sg}$ gives the main contribution to the neutron EDM compared to the other operators, and also that the contributions of $O_{ug}$ and $O_{3g}$ cancel out each other. It is pointed out that the inclusion of second lightest neutral Higgs scalar adding to the light…
The electric dipole moment of the muon ($d_μ$) is evaluated in a two Higgs doublet model with a softly broken discrete symmetry. The leading contributions from both one loop and two loop diagrams are considered. For $\tanβ\equiv |v_2|/|v_1|$ close to one, contributions from two loop diagrams involving the $t$ quark and the $W$ boson dominate; while for $\tanβ\agt 10$, contributions from two loop diagrams involving the $b$ quark and the $τ$ lepton are dominant. In these two regions, $d_μ\approx (m_μ/m_e) d_e$. For $8 \agt \tanβ\agt 4$, significant cancellation occurs among the contributions fro…
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…
An appended sector of two octet-colored scalars, each an electroweak doublet, is an interesting extension of the simple two Higgs doublet model motivated by the minimal flavor violation. Their rich CP violating interaction gives rise to a sizable electron electric dipole moment, besides the quark electric dipole moment via the two-loop contribution of Barr-Zee mechanism.
We analyze CP-violating effects in both Electric Dipole Moment (EDM) measurements and future analyses at the Large Hadron Collider (LHC) assuming a Two-Higgs-Doublet Model (2HDM) with "soft" CP-violation. Our analysis of EDMs and current LHC constraints shows that, in the case of a 2HDM Type II and Type III, an $\mathcal{O}(0.1)$ CP-violating phase in the Yukawa interaction between $H_1$ (the $125~\textrm{GeV}$ Higgs boson) and fermions is still allowed. For these scenarios, we study CP-violating effects in the neutron EDM and $t\bar{t}H_1$ production at the LHC. Our analysis shows that such a…
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…
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.
I consider contributions to the neutron electric dipole moment within Two Higgs Doublet Models which allow for small flavor changing neutral Higgs couplings. In a previous paper, I considered flavor changing interactions for the Standard Model Higgs boson to first order in the flavor changing coupling. In that paper I found that the obtained value of the neutron electric dipole moment were below the present experimental limit, given previous restrictions on such couplings. Because this was an effective theory, the result depended on an ultraviolet cut off $Λ$, parametrized as $ln(Λ^2)$. In the…
We propose a CP-violating source in the charged Higgs sector of a 3-Higgs Doublet Model (3HDM) that will contribute to three CP-asymmetry observables for low energy processes. In the context of such a 3HDM, a measurement of one of the specific asymmetry observables (i.e., $\bar{B} \to X_{s+d} γ$) could obtain up to 2.5% or more, which would give a 5$σ$ evidence for physics Beyond the SM (BSM) from the full BELLE II data set. In addition to these CP-violating observables, the current measurements of Electron Dipole Moments (EDMs) constrain the available parameter region of the CP-violating 3HDM…
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 investigate the effects of the new scalars in a two-Higgs-doublet model on the weak magnetic dipole moments of the fermions at the $Z$ peak. Proportionality of the Yukawa couplings to the fermion masses, and to $\tanβ$, makes such effects more important for the third family, and potentially relevant. For the $τ$ lepton, the new diagrams are suppressed by $v_τ= 2 \sin^2 θ_W - 1/2$, or by powers of $m_τ/M_Z$, but may still be comparable to the SM electroweak contributions. In contrast, we find that the new contributions for the bottom quark may be much larger than the SM electroweak contribut…
In several frameworks for leptons-sectors of two Higgs doublet models, we calculate the magnetic dipole moment for the different flavor types of neutrino. Computations are carried out by assuming a normal hierarchy for neutrino masses, and analyzing the process $ν\rightarrow νγ$ with a charged Higgs boson into the loop. The analysis was performed by sweeping the charged Higgs mass and taking into account the experimental constraints for relevant parameters in Two Higgs Doublet Models with and without flavor changing neutral currents; obtaining magnetic dipole moments close to the experimental …
The contributions of a second Higgs doublet to the electron electric dipole moment near the heavy Higgs decoupling limit are determined within an effective field theory framework. In models that satisfy the Glashow-Weinberg condition, the leading contributions in this limit at effective dimension six are shown to come from two-loop Barr-Zee diagrams that include the Standard Model-like Higgs boson. Additional diagrams that include heavy Higgs bosons are sub-leading and contribute only at effective dimension eight near the decoupling limit. This simplification implies that to leading order in t…
Flavour- and CP-violating electromagnetic or chromomagnetic dipole operators in the quark sector are generated in a large class of new physics models and are strongly constrained by measurements of the neutron electric dipole moment and observables sensitive to flavour-changing neutral currents, such as the $B\to X_sγ$ branching ratio and $ε'/ε$. After a model-independent discussion of the relevant constraints, we analyze these effects in models with partial compositeness, where the quarks get their masses by mixing with vector-like composite fermions. These scenarios can be seen as the low-en…
The leptonic branching fractions of the tau lepton are sensitive to anomalous charged current interactions. We use recent experimental measurements to determine the weak charged current magnetic and electric dipole moments and the Michel parameter $η$ with unprecedented precision. These results are then used to constrain the tau compositeness scale and the allowed parameter space for Higgs doublet models.
