arXiv subjects

T. Barakat

Publications and source records attributed to T. Barakat.

At least 19 recordsLinked to original sources

arXiv2021

Strong $B_{QQ'}^B_{QQ'}V$ vertices and the radiative decays of $B_{QQ}^ \to B_{QQ}γ$ in the light-cone sum rules

The strong coupling constants of spin-3/2 to spin-1/2 doubly heavy baryon transitions with light vector mesons are estimated within the light-cone QCD sum rules method. Moreover, using the vector-meson dominance ansätz, the widths of radiative decays $B_{QQ}^* \to B_{QQ} γ$ are calculated. The results for the said decay widths are compared to the predictions of other approaches.

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arXiv2020

Gravitational formfactors of the $ ρ$ meson in QCD sum rules

By using the quark part of the energy-momentum tensor current, the gravitational formfactors of the $ ρ$ meson are calculated within the light-cone sum rules method. In the considered version, the energy-momentum tensor current is not conserved and as a result, there appear nine formfactors, six (three) of which correspond to the conservation (nonconservation) of the energy-momentum tensor current. We also compare our results with the one existing in the literature.

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arXiv2020

$γ^* N \rightarrow Δ^{+}(1600)$ transition form factors in light-cone sum rules

The form factors of $γ^* N \rightarrow Δ(1600)$ transition is calculated within the light-cone sum rules assuming that $Δ^+(1600)$ is the first radial excitation of $Δ(1232)$. The $Q^2$ dependence of the magnetic dipole $\tilde{G}_M(Q^2)$, electric quadrupole $\tilde{G}_E(Q^2)$, and Coulomb quadrupole $\tilde{G}_c(Q^2)$ form factors are investigated. Moreover, the $Q^2$ dependence of the ratios $R_{EM} = -\frac{\tilde{G}_E(Q^2)}{\tilde{G}_M{Q^2}}$ and $R_{SM} = - \frac{1}{4 m_{Δ(1600)}^2} \sqrt{4 m_{Δ(1600)}^2 Q^2 + (m_{Δ(1600)}^2 - Q^2 - m_N^2)^2} \frac{\tilde{G}_c(Q^2)}{\tilde{G}_M(Q^2)}$ are studied. Finally, our predictions on $\tilde{G}_M(Q^2)$, $\tilde{G}_E(Q^2)$, and $\tilde{G}_C(Q^2)$ are compared with the results of other theoretical approaches.

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arXiv2019

Properties of excited $B_c$ states in QCD

The mass and leptonic decay constants of recently observed two new excited $B_c$ states at LHC are studied within the QCD sum rules. Considering the contributions of the ground and radially excited states, the mass and residues of the excited states of pseudoscalar and vector mesons are calculated in the framework of two different approaches of the QCD sum rules, namely, linear combinations of the corresponding sum rules and its derivatives as well as QCD sum rules with the incorporation of the least square fitting method. The obtained results on mass $m_{B_c^+}(2S) = 6.88 \pm 0.03~\rm{GeV} $ and $m_{B_c^{*+}}(2S) = 6.94 \pm 0.03~\rm{GeV} $ are in good agreement with the experimental data. Our predictions for the decay constants of these states are: $f_{B_c^+}(2S) = 0.42 \pm 0.02~\rm{GeV} $ and $f_{B_c^{*+}}(2S) = 0.46 \pm 0.01~\rm{GeV}$, which can be checked at future experiments to be conducted at the LHC. Comparison of our results with the predictions of the other approaches on mass and residues is also presented.

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arXiv2019

$N^*(1535) \rightarrow N $ transition form-factors due to the axial current

The form-factors for the transition $ N^*(1535)\to N $ induced by isovector and isoscalar axial currents within the framework of light-cone QCD sum rules by using the most general form of the interpolating current are calculated. In numerical calculations, we use two sets of values of input parameters. It is observed that the $ Q^2 $ dependence of the form-factor $ G_A $ can be described by the dipole form. Moreover, the form-factors $ G_P^{(S)} $ are found to be highly sensitive to the variations in the auxiliary parameter $ β$.

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arXiv2019

Radiative decays of the p-wave charmed heavy baryons

The radiative decays of the p-wave charmed heavy baryons to the ground state baryon states are studied in the framework of the light cone QCD sum rules method. Firstly, the transition form factors that describe these transitions are estimated, and then using these form factors the corresponding decay widths are calculated. A comparison of our results on the decay widths with those predicted by the other approaches existing in literature is performed.

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arXiv2019

Study of the $Λ_{b} \to N^\ast \ell^+ \ell^- $ decay in light cone sum rules

The form factors of the $Λ_{b} \to N^\ast \ell^+ \ell^-$ decay are calculated in the framework of the light cone QCD sum rules. In the calculations the contribution of the negative parity $Λ_b^\ast$ baryon is eliminated by constructing the sum rules for different Lorentz structures. Furthermore the branching ratio of the semileptonic $Λ_b \to N^\ast \ell^+ \ell^-$ decay is calculated. The numerical study for the branching ratio of the $Λ_{b} \to N^\ast \ell^+ \ell^-$ decay indicates that it is quite large and could be measurable at future planned experiments to be conducted at LHCb.

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arXiv2018

Form factors for the rare $Λ_{b}(Λ_{b}^*)\rar N\ell^+\ell^- $ decays in light cone QCD sum rules

Form factors of the rare $Λ_{b}(Λ_{b}^*)\to N\ell^{+}\ell^{-}$ decays are calculated in the framework of the light cone QCD sum rules by taking into account of the contributions from the negative parity baryons. Using the obtained results on the form factors, the branching ratios of the considered decays are estimated. The numerical survey for the branching ratios of the $Λ_b \rar N\ell^+\ell^- $ and $Λ_b^\ast \rar N\ell^+\ell^- $ decays indicate that these transitions could be measurable in LHCb in near future. Comparison of our predictions on the form factors and branching ratios with those existing in the literature is also performed.

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arXiv2017

Rare $Λ_{b}\to Λ\ell^{+}\ell^{-}$ decay in the two-Higgs doublet model of type-III

The rare exclusive dileptonic $Λ_{b}\to Λ\ell^{+}\ell^{-}$ $(\ell =μ, τ)$ decays are investigated in the general two-Higgs-doublet model of type III. A significant enhancement to the branching ratios, differential branching ratios, leptons forward-backward asymmetry, and the $Λ$ baryon polarizations over the standard model is obtained. Measurements of these quantities will be useful for establishing the two-Higgs doublet model.

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arXiv2016

Magnetic dipole moments of the negative parity $J^{PC}=2^{--}$ mesons in QCD

Magnetic dipole moments of the negative parity light and heavy tensor mesons are calculated within the light cone QCD sum rules method. The results are compared with the positive parity counterparts of the corresponding tensor mesons. The results of the analysis show that the magnetic dipole moments of the negative parity light mesons are smaller compared to those of the positive parity mesons. Contrary to the light meson case, magnetic dipole moments of the negative parity heavy mesons are larger than the ones for the positive parity mesons.

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arXiv2016

Strong coupling constant of negative parity nucleon with $π$ meson in light cone QCD sum rules

We estimate strong coupling constant between the negative parity nucleons with $π$ meson within the light cone QCD sum rules. A method for eliminating the unwanted contributions coming from the nucleon--nucleon and nucleon--negative parity nucleon transition is presented. It is observed that the value strong coupling constant of the negative parity nucleon $N^\ast N^\ast π$ transition is considerably different from the one predicted by the 3--point QCD sum rules, but is quite close to the coupling constant of the positive parity $N N π$ transition.

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arXiv2016

The Higgs Boson Mass from Three-loop Effective Potential of Massless Standard Model

The effective potential of massless standard model (SM) is calculated up to three-loop order. The stability of the effective potential and the Higgs boson mass are investigated up to three-loop order. We found that, Higgs boson mass $m_{H}$ of one-loop order is large. The two-loop and three-loop results are not appreciably different from each other. The two-loop and three-loop radiative corrections have led to an improvement of Higgs boson mass and the value of the scalar coupling. For the value $m_{t}=170$ GeV at the energy scale $μ\approx 5.68\times10^2$GeV, we get $m_{H2-loop}\approx 125.4$ GeV. At the energy scale $μ\geq28\times10^2$, the scalar coupling $λ$ at two-loop becomes negative and leads to metastable vacuum while the three-loop level is stable even at high $μ$ $\approx 10^{19}$ GeV. For the larger $μ$-range $(3 \times 10^{3} \text{GeV}\leq μ\leq 20 \times 10^{3} \text{GeV})$ spontaneous symmetry breaking for one-loop and three-loop occurs at approximately the same scalar coupling values. We get $m_{H1-loop}\approx 126.14$ GeV at $μ\approx 6.5 \times 10^{3}$ GeV while for three-loop $m_{H3-loop}\approx 126$ GeV at $μ\approx 20 \times 10^{3}$ GeV.

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arXiv2016

Analysis of the radiative decays $Σ_Q \to Λ_Q γ$ and $Ξ^\prime_Q \to Ξ_Q γ$ in light cone sum rules

The light cone sum rules method is used in studying the radiative decays $Σ_Q \to Λ_Q γ$ and $Ξ^\prime_Q \to Ξ_Q γ$. Firstly, the sum rules for the form factor $F_2(Q^2=0)$ responsible for these transitions is constructed. Using this result the decay widths of the above--mentioned decays are calculated and analyzed. A comparison of our predictions on the decay widths of considered transitions with the predictions of the other approaches is presented.

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arXiv2015

Determination of the $Σ$--$Λ$ mixing angle from QCD sum rules

The $Σ$--$Λ$ mixing angle is calculated in framework of the QCD sum rules. We find that our prediction for the mixing angle is $(1.00\pm 0.15)^0$ which is in good agreement with the quark model prediction, and approximately two times larger than the recent lattice QCD calculations.

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arXiv2015

Magnetic dipole moments of the heavy tensor mesons in QCD

The magnetic dipole moments of the ${\cal D}_2$, and ${\cal D}_{S_2}$, ${\cal B}_2$, and ${\cal B}_{S_2}$ heavy tensor mesons are estimated in framework of the light cone QCD sum rules. It is observed that the magnetic dipole moments for the charged mesons are larger than that of its neutral counterpart. It is found that the $SU(3)$ flavor symmetry violation is about 10\% in both $b$ and $c$ sectors.

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arXiv2015

Inhomogeneous and Homogeneous Renormalization Group Equations for the Effective Potential

The inhomogeneous renormalization group equation for the effective potential is rederived. It is shown that when the effective potential is normalized by the normalization condition on the generating functional, its renormalization group equation is homogeneous. This is demonstrated in the case of massive $ϕ^4$-theory. We also show that for the case of spontaneous symmetry breaking, the normalized effective potential is completely different from the symmetric case, though the two cases satisfy the same RGE with the same RG-functions. It is concluded that the vacuum energy density arises only in the case of SSB.

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arXiv2015

Diagonal and transition magnetic moments of negative parity heavy baryons in QCD sum rules

Diagonal and transition magnetic moments of the negative parity, spin-1/2 heavy baryons are studied in framework of the light cone QCD sum rules. By constructing the sum rules for different Lorentz structures, the unwanted contributions coming from negative (positive) to positive (negative) parity transitions are removed. It is obtained that the magnetic moments of all baryons, except $Λ_b^0$, $Σ_c^+$ and $Ξ_c^{\prime +}$, are quite large. It is also found that the transition magnetic moments between neutral negative parity heavy $Ξ_Q^{\prime 0}$ and $Ξ_Q^0$ baryons are very small. Magnetic moments of the $Σ_Q \to Λ_Q$ and $ Ξ_Q^{\prime \pm} \to Ξ_Q^\pm$ transitions are quite large and can be measured in further experiments.

hep-ph↗

arXiv2015

Transition magnetic moments between negative parity heavy baryons

The transition magnetic moments between negative parity, spin-1/2 heavy baryons are studied in framework of the light cone QCD sum rules. By constructing the sum rules for different Lorentz structures, the unwanted contributions coming from negative (positive) to positive (negative) parity transitions are removed. It is found that the magnetic moments between neutral negative parity heavy $Ξ_Q^{\prime 0}$ and $Ξ_Q^0$ baryons are very small. Magnetic moments of the $Σ_Q \to Λ_Q$ and $ Ξ_Q^{\prime \pm} \to Ξ_Q^\pm$ transitions are quite large and can be measured in further experiments.

hep-ph↗