Related papers: The $\gamma^* \gamma^*\to\eta_c$ transition form f…
We scrutinize recent findings on the charged-pion elastic form factor and the form factors entering in neutral-meson-to-photons transition amplitudes within the framework of QCD sum rules.
The purely nonperturbative soft contribution to the $\gamma^* p \to \Delta^+$ transition form factors is estimated using the local quark-hadron duality approach. Our results show that the soft contribution is dominated by the magnetic…
This is a short review of some hard two-photon processes: $\\ a) \,\,\gamma\gamma\to {\overline P}_1 P_2,\,\, {\overline P}_1 P_2= \{\pi^+\pi^-, K^+ K^-, K_S K_S, \pi^o\pi^o, \pi^o\eta\}\,, \\ b) \,\,\gamma\gamma\to V_1 V_2,\,\, V_1…
We propose that the different angular distributions in two-photon collisions observed at low and high center-of-mass energies $W_{\gamma\gamma}$ indicate the transition from nonperturbative to perturbative QCD. We calculate the differential…
We discuss the QCD sum-rule approach for the spacelike electromagnetic pion form factor in the $O(\alpha_s)$ approximation. We show that the nonlocality of the condensates is a key point to include nonperturbative contributions to the pion…
We calculate the semileptonic form factors $f_+^{B\to \eta}(q^2)$ and $f_+^{B\to \eta'}(q^2)$ from QCD sum rules on the light-cone (LCSRs), to NLO in QCD, and for small to moderate q^2, $0\leq q^2\leq 16 {\rm GeV}^2$. We include in…
In this paper, we calculate the vector, axial-vector and tensor form factors of $P\to T$ transition within the standard light-front~(SLF) and covariant light-front~(CLF) quark models~(QMs). The self-consistency and Lorentz covariance of CLF…
We calculate the transition form factors of the semileptonic $B_c\rightarrow \chi_{c2} l \bar{\nu} $ in the framework of QCD sum rules taking into account the two-gluon condensate corrections. Using the obtained results of form factors we…
We calculate the $\pi^0\to \gamma^*\gamma^*$ transition form factor ${\cal F}_{\pi^0\gamma^*\gamma^*}(q_1^2,q_2^2)$ in lattice QCD with two flavors of quarks. Our main motivation is to provide the input to calculate the $\pi^0$-pole…
In this article, we calculate the scalar form-factor of the proton in the framework of the light-cone QCD sum rules approach with the three valence quark light-cone distribution amplitudes up to twist-6, and observe the scalar form-factor…
We investigate space- and time-like form factors for $\omega\to\pi\gamma^*$ and $K^*\to K\gamma^*$ decays using the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The momentum…
Relativistic integral representation in terms of experimental neutron-proton scattering phase shifts is used to compute the charge form factor of the deuteron $ G_{Cd}(Q^2)$. The results of numerical calculations of $|G_{Cd}(Q^2)|$ are…
We consider the pion-photon transition form factor at low to intermediate spacelike momenta within the theoretical framework of light-cone sum rules. We derive predictions which take into account all currently known contributions stemming…
By using the 3-point QCD sum rules, we calculate the transition form factors of $D$ decays into the spin triplet axial vector mesons $a_1(1260)$, $f_1(1285) $, $f_1(1420)$. In the calculations, we consider the quark contents of each meson…
In this work, we perform a detailed study of transition form factors for axial-vector meson production via the two-photon fusion process $\gamma^* \gamma^* \to 1^{++}$, with space-like virtual photons in the initial state and a $P$-wave…
We investigate the transition to perturbative QCD in Compton processes, by concentrating on the specific reactions $\pi \gamma \to \pi \gamma$ and pion photoproduction at moderate energy scales. New sum rules for each of the helicities…
We perform joint fits using measurements of the proton structure functions $F_2(x,Q^2)$ and $F_L(x,Q^2)$, of the photon structure function $F_2^\gamma(x,Q^2)$ and of the total cross-sections $\sigma\left( \gamma p \rightarrow X\right)$ and…
Factorization scheme analysis of $F_2^{\gamma}(x,Q^2)$ in the next-to-leading order QCD is revisited. It is emphasized that the presence of the inhomogeneous term in the evolution equations for quark distribution functions of the photon…
We analyze effects due to transverse degrees of freedom in QCD calculations of the fundamental hard exclusive amplitude of $\gamma^*\gamma \to \pi^0$ transition. A detailed discussion is given of the relation between the modified…
Subleading Isgur-Wise form factor $\tau(v\cdot v')$ at ${\cal O}(1/m_Q)$ for $\Lambda_b\to\Lambda_{c1}^{1/2,3/2}$ weak transition is calculated by using the QCD sum rules in the framework of the heavy quark effective theory (HQET), where…