Related papers: Form factor $\pi^0\to \gamma^* +\gamma^*$ at diffe…

The recently measured $\gamma\gamma^*\rightarrow \pi^0$ anomalous form factor is analyzed using the $D4/D8\bar{D8}$ holographic approach to QCD. The half-on-shell transition form factor is vector meson dominated and is shown to exactly tie…

We present the results of our recent analyses of the form factors F_pi(Q^2) and F_{P gamma}(Q^2), P = pi, eta, eta', within the local-duality version of QCD sum rules. To probe the expected accuracy of this method, we consider, in parallel…

A short review of leading term QCD predictions vs those of the handbag model for large angle cross sections \gamma\gamma --> P_2 P_1 (P is the pseudoscalar meson \pi^{\pm,o}, K^{\pm,o}, \eta), and for \gamma\gamma --> V_2 V_1 (V is the…

Polarized photon structure can be studied in the future polarized $e^{+}e^{-}$ colliding-beam experiments. We investigate the spin-dependent structure function of the virtual photon $g_1^{\gamma}(x,Q^2,P^2)$, in perturbative QCD for…

Using the approach based on conformal symmetry we calculate the two-loop coefficient function for the axial-vector contributions to two-photon processes in the $\overline{\rm MS}$ scheme. This is the last missing element for the complete…

We present the status of the Mainz group's lattice QCD calculation of the pion transition form factor $\mathcal{F}_{\pi^0\gamma^\ast\gamma^\ast}$, which describes the interaction of an on-shell pion with two off-shell photons. This form…

Measurements of the QED structure of the photon based on the reaction ee --> ee \gamma(*)(P^2)\gamma*(Q^2) --> ee mumu are discussed. This review is an update of the discussion of the results on the QED structure of the photon presented in…

We report results on the $\pi$-$\gamma$ transition form factor obtained within the hard scattering approach including transverse momentum effects and Sudakov corrections. The results clearly favor distribution amplitudes close to the…

We present a theoretical study of the $\gamma\gamma^{*} \to \pi^+\pi^-, \pi^0\pi^0$ processes from the threshold through the $f_2(1270)$ region in the $\pi\pi$ invariant mass. We adopt the Omn\`es representation in order to account for…

Dalitz decays of $\omega$ and $\rho$ mesons, $\omega\to \pi^0\gamma^*\to\pi^0 e^+e^-$ and $\rho^0\to \pi^0\gamma^*\to\pi^0 e^+e^-$, produced in $pp$ collisions are calculated within a covariant effective meson-nucleon theory. We argue that…

We derive the light-front wave function (LFWF) representation of the $\gamma^* \gamma^* \to \eta_c(1S)\,,\eta_c(2S)$ transition form factor $F(Q_1^2, Q_2^2)$ for two virtual photons in the initial state. For the LFWF, we use different…

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…

We calculate the one-photon loop radiative corrections to the neutral pion-pair photoproduction process $\pi^-\gamma \to \pi^-\pi^0\pi^0$. At leading order this reaction is governed by the chiral pion-pion interaction. Since the chiral…

We present a next-to-leading order calculation of jet production in gamma^*gamma collisions from e+e- scattering in a region where the virtuality Q^2 of the probing virtual photon is small compared to the transverse jet energy. The…

Motivated by the ongoing measurements of the Primakoff process pi- gamma* --> pi- pi0 by COMPASS collaboration at CERN, the transition form factor for the canonical anomalous process gamma* --> pi+ pi0 pi- is calculated in a constituent…

Assuming the form $\sigma^{\gamma P} \propto l^{\lambda_{\rm eff}}$ at fixed $Q^2$ for the behavior of the virtual-photon proton scattering cross section, where $l$ is the coherence length of the photon fluctuations, it is seen that the…

The sum rule for the first moment of the polarised (virtual) photon structure function $g_1^\gamma(x,Q^2;K^2)$ is revisited in the light of proposals for future $e^+ e^-$ colliders. The sum rule exhibits an array of phenomena characteristic…

We propose an interpolating formula for the amplitude induced by the axial anomaly, concentrating on the $\pi^0\gamma^{\ast}\gamma^{\ast}$ transition form factor. The QCD corrections to this amplitude are generally described by two major…

The pion form factor at very large $Q^2$ is obtained by using a new pion wave function. It shows that when $Q^2>>(1.8GeV)^2$ the pion form factor reaches the asymptotic limit ${\alpha_s(Q^2)\over Q^2}$

We perform a lattice QCD calculation of the \pi^0\to\gamma\gamma transition form factor and the associated decay width. We use a Euclidean time integral of the relevant three-point function to compute the decay amplitude for two-photon…