arXiv subjects

K. Azizi

Publications and source records attributed to K. Azizi.

At least 235 records · Page 13Linked to original sources

arXiv2016

On the strong coupling $N^{()}N^{()}π$

We study the strong vertices $N^*Nπ$, $N^*N^*π$ and $NNπ$ in QCD, where $N^*$ denotes the negative parity $N (1535)$ state. We use the most general form of the interpolating currents to calculate the corresponding strong coupling constants. It is obtained that the coupling associated to $N^*Nπ$ vertex is strongly suppressed compared to those related to two other vertices. The strong coupling corresponding to $N^*N^*π$ is obtained to be roughly half of that of $NNπ$ vertex. We compare the obtained results on $N^*Nπ$ and $NNπ$ vertices with the existing predictions of other theoretical studies as well as those extracted from the experimental data.

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arXiv2016

Thermal behavior of the mass and residue of hyperons

We investigate the mass and residue of the $Σ$, $Λ$ and $Ξ$ hyperons at finite temperature in the framework of thermal QCD sum rules. In our calculation, we take into account the additional operators coming up at finite temperature. We find the temperature-dependent continuum threshold for each hyperon using the obtained sum rules for their mass and residue. The numerical results demonstrate that the mass and residue of the particles under consideration remain stable up to a certain temperature, after which they decrease by increasing the temperature.

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arXiv2015

Comparative analysis of the $Λ_b \rightarrow Λ\ell^+ \ell^-$ decay in the SM, SUSY and RS model with custodial protection

We comparatively analyze the rare $Λ_b\rightarrow Λ\ell^+ \ell^-$ channel in standard model, supersymmetry and Randall-Sundrum model with custodial protection (RS$_c$). Using the parametrization of the matrix elements entering the low energy effective Hamiltonian in terms of form factors, we calculate the corresponding differential decay width and lepton forward-backward asymmetry in these models. We compare the results obtained with the most recent data from LHCb as well as lattice QCD results on the considered quantities. It is obtained that the standard model, with the form factors calculated in light-cone QCD sum rules, can not reproduce some experimental data on the physical quantities under consideration but the supersymmetry can do it. The RS$_c$ model predictions are roughly the same as the standard model and there are no considerable differences between the predictions of these two models. In the case of differential decay rate, the data in the range $4 $ GeV$^2/$c$^4\leq$ $q^2 \leq 6$ GeV$^2/$c$^4$ can not be described by any of the considered models.

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arXiv2015

Strong $D^{}_sD_{s}η^{(\prime)}$ and $B^{}_sB_{s}η^{(\prime)}$ vertices from QCD light-cone sum rules

The strong $D^{*}_sD_{s}η^{(\prime)}$ and $B^{*}_sB_{s}η^{(\prime)}$ vertices are studied and the relevant couplings are calculated in the context of the light-cone QCD sum rule method with twist-4 accuracy by including the next-to-leading order corrections. In the analysis, both the quark and gluon components of the $η$ and $η^{\prime}$ mesons and the axial anomaly corrected higher twist distributions are included.

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arXiv2015

Strong $Σ_bNB$ and $Σ_cND$ coupling constants in QCD

We study the strong interactions among the heavy bottom spin--1/2 $Σ_b$ baryon, nucleon and $B$ meson as well as the heavy charmed spin--1/2 $Σ_c$ baryon, nucleon and $D$ meson in the context of QCD sum rules. We calculate the corresponding strong coupling form factors defining these vertices by using a three point correlation function. We obtain the numerical values of the corresponding strong coupling constants via the most prominent structure entering the calculations.

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arXiv2015

Positive and negative parity hyperons in nuclear medium

The effects of nuclear medium on the residue, mass and self energy of the positive and negative parity $Σ$, $Λ$ and $Ξ$ hyperons are investigated using the QCD sum rule method. In the calculations, the general interpolating currents of hyperons with an arbitrary mixing parameter are used. We compare the results obtained in medium with those of the vacuum and calculate the shifts in the corresponding parameters. It is found that the shifts on the residues in nuclear matter are over all positive for both the positive and negative parity hyperons, except for the positive parity $Σ$ hyperon that the shift is negative. The shifts on the masses of these baryons are obtained to be negative. The shifts on the residues and masses of negative parity states are large compared to those of positive parities. The maximum shift belongs to the residue of the negative parity $Λ$ hyperon. The vector self-energies gained by the positive parity baryons are large compared to the negative parities' vector self-energies. The maximum value of the vector self-energy belongs to the positive parity $Σ$ hyperon. The numerical values are compared with the existing predictions in the literature.

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arXiv2015

Modifications on nucleon parameters at finite temperature

Taking into account the additional operators coming up at finite temperature, we investigate the mass and residue of the nucleon in the framework of thermal QCD sum rules. We observe that the mass and residue of the nucleon are initially insusceptible to increase of temperature, however after a certain temperature, they start to fall increasing the temperature.

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arXiv2015

Strong couplings of negative and positive parity nucleons to the heavy baryons and mesons

The strong coupling form factors related to the strong vertices of the positive and negative parity nucleons with the heavy $Λ_{b[c]}[Σ_{b[c]}]$ baryons and heavy $B^*[D^*]$ vector mesons are calculated using a three-point correlation function. Using the values of the form factors at $Q^2=-m^2_{meson}$ we compute the strong coupling constants among the participating particles.

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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.

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arXiv2015

Radiative transition of negative to positive parity nucleon

We investigate the $N^{\ast}(1535)\rightarrow Nγ$ transition in the framework of light cone QCD sum rules. In particular, using the most general form of the interpolating current for the nucleon as well as the distribution amplitudes of the photon, we calculate two transition form factors responsible for this channel and use them to evaluate the decay width and branching ratio of the transition under consideration. The result obtained for the branching fraction is in a good consistency with the experimental data.

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arXiv2015

Magnetic moments of negative parity heavy baryons in QCD

The magnetic moments of the negative parity, spin-1/2 baryons containing single heavy quark are calculated. The pollution that occur from the transitions between positive and negative parity baryons are removed by constructing the sum rules from different Lorentz structures.

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arXiv2015

Thermal properties of light tensor mesons via QCD sum rules

The thermal properties of $f_{2}(1270)$, $a_{2}(1320)$ and $K_2^*(1430)$ light tensor mesons are investigated in the framework of QCD sum rules at finite temperature. In particular, the masses and decay constants of the light tensor mesons are calculated taking into account the new operators appearing at finite temperature. The numerical results show that at the point which the temperature-dependent continuum threshold vanishes, the decay constants decrease with amount of $(70-85)\%$ compared to their vacuum values, while the masses diminish about $(60-72)\%$ depending on the kinds of the mesons under consideration. The results obtained at zero temperature are in good consistency with the experimental data as well as existing theoretical predictions.

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arXiv2015

Semileptonic $B_{s} \rightarrow D_{s2}^{*}(2573)\ell\barν_{\ell}$ transition in QCD

We analyze the semileptonic $ B_{s} \rightarrow D_{s2}^{*}(2573)\ell\bar{ν}_{\ell}$ transition, where $\ell=τ,~μ$ or $e$, within the standard model. We apply the QCD sum rule approach to calculate the transition form factors entering the low energy Hamiltonian defining this channel. The fit functions of the form factors are used to estimate the total decay widths and branching fractions in all lepton channels. The orders of branching ratios indicate that this transition is accessible at LHCb in near future.

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arXiv2015

Semileptonic $B \rightarrow \bar{D} $ transition in nuclear medium

We study the semileptonic tree-level $B \rightarrow \bar{D}$ transition in the framework of QCD sum rules in nuclear medium. In particular, we calculate the in-medium form factors entering the transition matrix elements defining this decay channel. It is found that the interactions of the participating particles with the medium lead to a considerable suppression in the branching ratio compared to the vacuum.

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arXiv2015

Thermal behaviors of light unflavored tensor mesons in the framework of QCD sum rule

In this study, we investigate the sensitivity of the masses and decay constants of the light $f_{2}(1270)$ and $a_{2}(1320)$ tensor mesons to the temperature using QCD sum rule approach. In our calculations, we take into account the additional operators appearing in operator product expansion at finite temperature. It is obtained that at deconfinement temperature the decay constants and masses decrease with amount of $6\%$ and $96\%$ compared to their vacuum values, respectively. Our results on the masses at zero temperature are consistent with the vacuum sum rules predictions as well as the experimental data.

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arXiv2014

The strong $Λ_bNB$ and $Λ_cND$ vertices

We investigate the strong vertices among $Λ_b$, nucleon and $B$ meson as well as $Λ_c$, nucleon and $D$ meson in QCD. In particular, we calculate the strong coupling constants $g_{Λ_bNB}$ and $g_{Λ_cND}$ for different Dirac structures entered the calculations. In the case of $Λ_cND$ vertex, the result is compared with the only existing prediction obtained at $Q^2=0$.

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arXiv2014

Radiative $Ω_{Q}^{}\rightarrowΩ_{Q}γ$ and $Ξ_{Q}^{}\rightarrowΞ^{\prime}_{Q}γ$ transitions in light cone QCD

We calculate the magnetic dipole and electric quadrupole moments associated with the radiative $Ω_{Q}^{*}\rightarrowΩ_{Q}γ$ and $Ξ_{Q}^{*}\rightarrowΞ^{\prime}_{Q}γ$ transitions with $Q=b$ or $c$ in the framework of light cone QCD sum rules. It is found that the corresponding quadrupole moments are negligibly small while the magnetic dipole moments are considerably large. A comparison of the results on the considered multipole moments as well as corresponding decay widths with the predictions of the vector dominance model is performed.

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arXiv2014

Analysis of the strong $D_{2}^{}(2460)^{0}\rightarrow D^+ π^- $ and $D_{s2}^{}(2573)^{+}\rightarrow D^{+} K^{0}$ transitions via QCD sum rules

The strong $D_{2}^{*}(2460)^{0}\rightarrow D^+ π^- $ and $D_{s2}^{*}(2573)^{+}\rightarrow D^{+} K^{0}$ transitions are analyzed via three point QCD sum rules. First, we calculate the corresponding strong coupling constants $g_{D_2^*Dπ}$ and $g_{D_{s2}^*DK}$. Then, we use them to calculate the corresponding decay widths and branching ratios. Making use of the existing experimental data on the ratio of the decay width in the pseudoscaler $D$ channel to that of the vector $D^*$ channel, finally, we estimate the decay width and branching ratio of the strong $D_2^*(2460)^0 \rightarrow D^*(2010)^+π^-$ transition.

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