Related papers: Pion Helicity Structure And Its Consequence For Th…
We consider the pion structure in the region of low and moderately high momentum transfers: at low $Q^2$, the pion is treated as a composite system of constituent quarks; at moderately high momentum transfers, $Q^2=10\div25\;GeV^2$, the…
We revisit the hard QCD contributions to the pion gravitational form factors (GFFs), in terms of the twist-2,3 pion distribution amplitudes (DA), including novel semi-hard contributions from the instantons. The pion DAs are evaluated in the…
Domain model of QCD allows for description of wide range of meson observables, dynamical chiral symmetry breaking, and resolution of $U_A(1)$ and strong $CP$ problems. The purpose of the present study is transition form-factor of neutral…
For deuteron electromagnetic form factors,perturbative QCD(pQCD) predicts that $G^{+}_{00}$ becomes the dominate helicity amplitude and that $G^{+}_{+0}$ and $G^{+}_{+-}$ are suppressed by factors $\Lambda_{\rm QCD}/Q$ and $\Lambda_{\rm…
The experimental and theoretical status of elastic electron scattering from the nucleon is reviewed. A wealth of new data of unprecedented precision, especially at small values of the momentum transfer, in parallel to new theoretical…
Recent BaBaR data on the pion transition form factor, whose Q^2 dependence is much steeper then predicted by asymptotic Quantum Chromodynamics (QCD), have caused a renewed interest in its theoretical description. We present here a formalism…
In many years ago, Isgur and Llewellyn Smith addressed that PQCD is inapplicable to exclusive processes, such as the pion form factor.The main problem is that the asymptotic of PQCD is only about one fourth of the experimental value. We…
Recent data for the ratio $R(Q)= QF_{2}(Q^{2})/F_{1}(Q^{2})$ shocked the community by disobeying expectations held for 50 years. We examine the status of perturbative QCD predictions for helicity-flip form factors. Contrary to common…
A selected set of topics along the borderline between perturbative and nonperturbative QCD in exclusive reactions are studied. Specific problems, related to different mechanisms of momentum transfer to an intact hadron, are discussed.…
We present an investigation of the pion's electromagnetic form factor F_{\pi}(Q^2) in the spacelike region utilizing two new ingredients: (i) a double-humped, endpoint-suppressed pion distribution amplitude derived before via QCD sum rules…
In this work, we employ a dispersion relation that allows to recover the electromagnetic form factor of the pion from its modulus along the unitarity cut. Unlike the standard dispersive approach, this method extends in a straightforward…
It is demonstrated that any attempt to calculate the perturbative QCD contribution to the pion form factor requires the inclusion of intrinsic transverse momentum besides Sudakov form factors. For momentum transfers of the order of a few…
We review the theory of hard exclusive scattering in Quantum Chromodynamics. After recalling the classical counting rules which describe the leading scale dependence of form factors and elastic reactions at fixed angle, the pedagogical…
The $\gamma^\ast \gamma \to \pi^0$ transition form factor, $G(Q^2)$, is computed on the entire domain of spacelike momenta using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory: the…
Recent experiment indicates that the behavior exhibited by the ratios $E_{1^+}/M_{1^+}$ and $S_{1^+}/M_{1^+}$ of the $\gamma^* N \leftrightarrow \Delta$ transition remain small and negative for $Q^2 \le 4.0 GeV^2$. It implies that the…
We present a combined analysis of the space- and time-like electromagnetic pion form factors in light-cone perturbative QCD with transverse momentum dependence and Sudakov suppression. Including the non-perturbative ``soft' QCD and power…
We explore the relationship between exclusive and inclusive electromagnetic scattering from the pion, focusing on the transition region at intermediate Q^2. Combining Drell-Yan data on the leading twist quark distribution in the pion with a…
At very high energy and wide angles, Compton scattering on the proton (gamma p -> gamma p) is described by perturbative QCD. The perturbative QCD calculation has been performed several times previously, at leading twist and at leading order…
In the framework of pertubative QCD it is argued that in the elastic $ed$-scattering at $Q^{2}\sim$ few $(GeV/c)^{2}$ the light-cone-frame helicity-flip amplitudes could not be omitted. The obtained $\frac{B}{A}$ ratio of Rosenbluth…
Using a holographic dual model of QCD, we compute the pion electromagnetic form factor F_pi(Q^2) in the spacelike momentum transfer region, as well as pion couplings to vector mesons g_rho^(n) pi pi. Spontaneous and explicit chiral symmetry…