Photon Distribution Amplitudes Research Articles

Magnetic dipole moments of the Ωc(3185)0 and Ωc(3327)0 states from molecular perspective

In this paper we study the magnetic dipole moments of the newly discovered Ωc(3185)0 and Ωc(3327)0, assuming that Ωc(3185)0 and Ωc(3327)0 are S-wave DΞ and D⁎Ξ molecular pentaquark states, respectively. Together with these states, the magnetic dipole moments of possible DsΞ, Ds⁎Ξ, DΞ⁎, and DsΞ⁎ pentaquark states are also studied. The magnetic dipole moments of these singly-charmed pentaquarks are estimated within the framework of the QCD light cone sum rules utilizing the photon distribution amplitudes. In the search for the properties of singly-charmed molecular pentaquark states, the results obtained for the magnetic dipole moments can be useful.

Electromagnetic form factors of the Bc-like tetraquarks: Molecular and diquark-antidiquark pictures

In this study, we use the molecular and diquark-antidiquark tetraquark pictures to investigate magnetic and quadrupole moments of the Bc-like ground state tetraquarks with the QCD light-cone sum rules with quantum numbers JP=1+. In the numerical analysis, to obtain the magnetic and quadrupole moments of Bc-like tetraquark states molecular and diquark-antidiquark forms of interpolating currents, and photon distribution amplitudes have been used. The magnetic moments are acquired as μZucu¯b¯Mol=1.18−0.40+0.52μN, μZucu¯b¯Di=3.05−0.95+1.19μN, μZdcd¯b¯Mol=0.32−0.10+0.18μN, and μZdcd¯b¯Di=2.38−0.75+0.95μN. The hadrons' magnetic and quadrupole moments are another fundamental observable as their mass, which provides information on the underlying quark structure and dynamics. The results obtained in both pictures are quite different from each other. Any experimental measurement of the magnetic moments can provide an understanding of the internal structure of these states. We get nonzero but small values for the quadrupole moments of Bc-like tetraquark states showing non-spherical charge distributions. Hopefully, the examinations given in this study will be helpful to an experimental search of them, which will be an interesting research subject.

Magnetic dipole moments of the Zc(4020)+ , Zc(4200)+ , Zcs(4000)+ and Zcs(4220)+ states in light-cone QCD

The magnetic dipole moments of the $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ states are extracted in the framework of the light-cone QCD sum rules. In the calculations, we use the hadronic molecular form of interpolating currents, and photon distribution amplitudes to get the magnetic dipole moment of $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ tetraquark states. The magnetic dipole moments are obtained as $\mu_{Z_{c}} = 0.66^{+0.27}_{-0.25}$, $\mu_{Z^{1}_{c}}=1.03^{+0.32}_{-0.29}$, $\mu_{Z_{cs}}=0.73^{+0.28}_{-0.26}$, $\mu_{Z^1_{cs}}=0.77^{+0.27}_{-0.25}$ for the $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ states, respectively. We observe that the results obtained for the $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ states are large enough to be measured experimentally. As a by product, we predict the magnetic dipole moments of the neutral $Z_{cs}(4000)$ and $Z_{cs}(4220)$ states. The results presented here can serve to be helpful knowledge in experimental as well as theoretical studies of the properties of hidden-charm tetraquark states with and without strangeness.

Magnetic dipole moments of the hidden-charm pentaquark states: P_c(4440), P_c(4457) and P_{cs}(4459)

In this work, we employ the light-cone QCD sum rule to calculate the magnetic dipole moments of the P_c(4440), P_c(4457) and P_{cs}(4459) pentaquark states by considering them as the diquark–diquark–antiquark and molecular pictures with quantum numbers J^P = frac{3}{2}^-, J^P = frac{1}{2}^- and J^P = frac{1}{2}^-, respectively. In the analyses, we use the diquark–diquark–antiquark and molecular form of interpolating currents, and photon distribution amplitudes to obtain the magnetic dipole moment of pentaquark states. Theoretical examinations on magnetic dipole moments of the hidden-charm pentaquark states, are essential as their results can help us better figure out their substructure and the dynamics of the QCD as the theory of the strong interaction. As a by product, we extract the electric quadrupole and magnetic octupole moments of the P_c(4440) pentaquark. These values show a non-spherical charge distribution.

QCD calculations of radiative heavy meson decays with subleading power corrections

We revisit QCD calculations of radiative heavy meson decay form factors by including the subleading power corrections from the twist-two photon distribution amplitude at next-to-leading-order in αs with the method of the light-cone sum rules (LCSR). The desired hard-collinear factorization formula for the vacuum-to-photon correlation function with the interpolating currents for two heavy mesons is constructed with the operator- product-expansion technique in the presence of evanescent operators. Applying the back- ground field approach, the higher twist corrections from both the two-particle and three- particle photon distribution amplitudes are further computed in the LCSR framework at leading-order in QCD, up to the twist-four accuracy. Combining the leading power “point- like” photon contribution at tree level and the subleading power resolved photon corrections from the newly derived LCSR, we update theory predictions for the nonperturbative couplings describing the electromagnetic decay processes of the heavy mesons H∗±→ H±γ, H∗0→ H0γ, {H_s^{ast}}^{pm } → {H}_s^{pm } γ (with H = D, B). Furthermore, we perform an exploratory comparisons of our sum rule computations of the heavy-meson magnetic couplings with the previous determinations based upon different QCD approaches and phenomenological models.

Magnetic moments of doubly heavy baryons in light-cone QCD

The magnetic dipole moments of the spin- doubly heavy baryons are extracted in the framework of the light-cone QCD sum rule using the photon distribution amplitudes. The electromagnetic properties of the doubly heavy baryons encodes important information of their internal structure and geometric shape. The results for the magnetic dipole moments of doubly heavy baryons acquired in this work are compared with the predictions of the other theoretical approaches. The agreement of the estimations with some (but not all) theoretical estimations is good.

The electromagnetic multipole moments of the possible charm-strange pentaquarks in light-cone QCD

We investigate the electromagnetic properties of possible charm-strange pentaquarks in the framework of the light-cone QCD sum rule using the photon distribution amplitudes. In particular, by calculating the corresponding electromagnetic form factors defining the radiative transitions under consideration we estimate the magnetic dipole and electric quadrupole moments of the pentaquark systems of a charm, an anti-strange and three light quarks. We observe that the values of magnetic dipole moments are considerably large, however, the quadrupole moments are very small. Any future measurements of the electromagnetic parameters under consideration and comparison of the obtained data with the theoretical predictions can shed light on the quark–gluon organization as well as the nature of the pentaquarks.

Gluon poles and photon distribution amplitudes in Drell-Yan-like processes

We calculate the hadron tensor related to the photon-induced Drell-Yan process, with incoming nucleon being transversally polarised. We predict the new single spin asymmetry which probes gluon poles and which is expressed in terms of photon (both chiral-odd and chiral-even) distribution amplitudes and chiral-odd nucleon function stemming from the nucleon transverse polarization.

Erratum to: Gluon poles and photon distribution amplitudes in Drell-Yan-like processes

Erratum to: Gluon poles and photon distribution amplitudes in Drell-Yan-like processes

Subleading-power corrections to the radiative leptonic B \u2192 \u03b3\u2113\u03bd decay in QCD

Applying the method of light-cone sum rules with photon distribution amplitudes, we compute the subleading-power correction to the radiative leptonic B → γℓν decay from the twist-two hadronic photon contribution at next-to-leading order in QCD; and further evaluate the higher-twist “resolved photon” corrections at leading order in αs, up to twist-four accuracy. QCD factorization for the vacuum-to-photon correlation function with an interpolating current for the B-meson is established explicitly at leading power in Λ/mb employing the evanescent operator approach. Resummation of the parametrically large logarithms of mb2/Λ2 entering the hard function of the leading-twist factorization formula is achieved by solving the QCD evolution equation for the light-ray tensor operator at two loops. The leading-twist hadronic photon effect turns out to preserve the symmetry relation between the two B → γ form factors due to the helicity conservation, however, the higher-twist hadronic photon corrections can yield symmetry-breaking effect already at tree level in QCD. Using the conformal expansion of photon distribution amplitudes with the non-perturbative parameters estimated from QCD sum rules, the twist-two hadronic photon contribution can give rise to approximately 30% correction to the leading-power “direct photon” effect computed from the perturbative QCD factorization approach. In contrast, the subleading-power corrections from the higher-twist two-particle and three-particle photon distribution amplitudes are estimated to be of mathcal{O}left(3sim 5%right) with the light-cone sum rule approach. We further predict the partial branching fractions of B → γℓν with a photon-energy cut Eγ ≥ Ecut, which are of interest for determining the inverse moment of the leading-twist B-meson distribution amplitude thanks to the forthcoming high-luminosity Belle II experiment at KEK.

The electromagnetic multipole moments of the charged open-flavor states

The electromagnetic multipole moments of the open-flavor states are investigated by assuming a diquark–antidiquark picture for their internal structure and quantum numbers for their spin-parity. In particular, their magnetic and quadrupole moments are extracted in the framework of light-cone QCD sum rule by the help of the photon distribution amplitudes. The electromagnetic multipole moments of the open-flavor states are important dynamical observables, which encode valuable information on their underlying structure. The results obtained for the magnetic moments of different structures are considerably large and can be measured in future experiments. We obtain very small values for the quadrupole moments of states indicating a nonspherical charge distribution.

Subleading power corrections to the pion-photon transition form factor in QCD

We reconsider QCD factorization for the leading power contribution to the γ*γ → π0 form factor Fγ*γ→π0(Q2) at one loop using the evanescent operator approach, and demonstrate the equivalence of the resulting factorization formulae derived with distinct prescriptions of γ5 in dimensional regularization. Applying the light-cone QCD sum rules (LCSRs) with photon distribution amplitudes (DAs) we further compute the subleading power contribution to the pion-photon form factor induced by the “hadronic” component of the real photon at the next-to-leading-order in mathcal{O}left({alpha}_sright) , with both naive dimensional regularization and ’t Hooft-Veltman schemes of γ5. Confronting our theoretical predictions of Fγ*γ→π0 (Q2) with the experimental measurements from the BaBar and the Belle Collaborations implies that a reasonable agreement can be achieved without introducing an “exotic” end-point behaviour for the twist-2 pion DA.

The Scalar Photon Light-Cone Distribution Amplitude in the Instanton Vacuum Model of QCD

Based on the principle of the Lorentz covariance, the transition matrix elements from an off-shell photon state to the vacuum are parameterized by the light-cone photon distribution amplitudes (DAs). Both the scalar off-shell photon light-cone DA and the corresponding coupling are calculated in the instanton vacuum model of quantum chromodynamics (QCD), and their explicit analytical expressions and the numerical results are given. The results for the other chiral-odd light-cone photon DAs and their couplings are presented as well.

Off-shell photon distribution amplitudes in the low-energy effective theory of QCD

Based on the principle of the Lorentz covariance the transition matrix elements from an off-shell photon state to the vacuum are decomposed into the light-cone photon DAs, in which only two transversal DAs survive in the on-shell limit. The eight off-shell light-cone photon distribution amplitudes (DAs) corresponding to chiral-odd and chiral-even up to twist-four and the corresponding coupling constants are studied systematically in the instanton vacuum model of quantum chromodynamics (QCD). The various individual photon DA multiplied by its corresponding coupling constant is expressed in terms of the correlation functions, which are connected with the spectral densities of an effective quark propagator, and then evaluated in the low-energy effective theory derived from the instanton vacuum model of QCD. The explicit analytical expressions and the numerical results for the photon DAs and their coupling constants are given.

Photon distribution amplitudes in nonlocal chiral quark model

Photon distribution amplitudes up to twist four are calculated within the nonlocal chiral quark model with a simple pole ansatz for momentum dependence of the constituent quark mass. Calculations are performed using modified electromagnetic vector current in order to satisfy Ward identities. Quark condensate and magnetic susceptibility of the QCD vacuum entering definitions of the distribution amplitudes are computed and compared with existing phenomenological estimates. Both real and off-shell photons are considered and relevant form factors are calculated. Our results are analytical up to the numerical solution of certain algebraic equation.

Photon distribution amplitudes and light-cone wave functions in chiral quark models

The leading- and higher-twist distribution amplitudes and light-cone wave functions of real and virtual photons are analyzed in chiral quark models. The calculations are performed in the nonlocal quark model based on the instanton picture of the QCD vacuum, as well as in the spectral quark model and the Nambu--Jona-Lasinio model with the Pauli-Villars regulator, which both treat interaction of quarks with external fields locally. We find that in all considered models the leading-twist distribution amplitudes of the real photon defined at the quark-model momentum scale are constant or remarkably close to the constant in the $x$ variable, thus are far from the asymptotic limit form. The QCD evolution to higher momentum scales is necessary and we carry it out at the leading order of the perturbative theory for the leading-twist amplitudes. We provide estimates for the magnetic susceptibility of the quark condensate ${\ensuremath{\chi}}_{\mathrm{m}}$ and the coupling ${f}_{3\ensuremath{\gamma}}$, which in the nonlocal model turn out to be close to the estimates from QCD sum rules. We find the higher-twist distribution amplitudes at the quark model scale and compare them to the Wandzura-Wilczek estimates. In addition, in the spectral model we evaluate the distribution amplitudes and light-cone wave functions of the $\ensuremath{\rho}$-meson.

Magnetic moment of theΘ+pentaquark state

We have calculated the magnetic moment of the recently observed $\Theta^+$ pentaquark in the framework of the light cone QCD sum rules using the photon distribution amplitudes. We find that $\mu_{\Theta^+}=(0.12\pm 0.06) \mu_N$, which is quite small. We also compare our result with predictions of other groups.

Photon distribution amplitudes in QCD

We develop a consistent technique for the calculation of real photon emission in hard exclusive processes, which is based on the background field formalism and allows a convenient separation of hard electromagnetic and soft hadronic components of the photon. The latter ones are related to matrix-elements of light-cone operators in the electromagnetic background field and can be parametrized in terms of photon distribution amplitudes. We construct a complete set of photon distribution amplitudes up to and including twist-4, for both chirality-conserving and chirality-violating operators. The distribution amplitudes involve several non-perturbative parameters and, most importantly, the magnetic susceptibility of the quark condensate. We review and update previous estimates of the susceptibility and also give new estimates of parameters describing higher-twist amplitudes from QCD sum rules.