相关论文: A Model For Two-Pion Photoproduction Amplitudes
We present the first numerical computation of two-loop amplitudes based on the unitarity method. As a proof of principle, we compute the four-gluon process. We discuss the new method, analyze its numerical properties and apply it to…
A dynamical coupled channel approach is used to study $\pi$ and $\omega$--meson production induced by pions and photons scattering from the proton. Six intermediate channels including $\pi N$, $\eta N$, $\pi\Delta$, $\sigma N$, $\rho N$ and…
In an unitary effective Lagrangian model we develop a unified description of both meson scattering and photon-induced reactions on the nucleon. Adding the photon to an already existing model for meson-nucleon scattering yields both Compton…
We present a lattice-QCD calculation of the long-distance two-photon contribution to the decay amplitude of a long-lived kaon to a pair of muons on a $24^3\times 64$ physical-pion-mass ensemble. In these proceedings, the theoretical…
It is shown that within a truncated partial wave analysis for photoproduction of two pseudoscalar mesons, it is possible to halve the number of independent partial amplitudes by taking into account parity conservation. In addition, within…
We consider the production of muon pairs from the scattering of pions on longitudinally polarized protons. We calculate the cross section and the single spin asymmetry for this process, taking into account pion bound state effects. We work…
A field-theoretical description of the photoproduction of two pions off the nucleon is presented that applies to real as well as virtual photons in the one-photon approximation. The Lorentz-covariant theory is complete at the level of all…
A Regge model with absorptive corrections is employed in a global analysis of the world data on the reactions gamma p -> pi0 p and gamma n -> pi0 n for photon energies from 3 to 18 GeV. In this region resonance contributions are expected to…
The exclusive production of \pi\pi and \pi\rho in hard \gamma^{\star}\gamma scattering in the forward kinematical region where the virtual photon is highly off-shell are studied through the \gamma\to\pi^- Transition Distribution Amplitudes.…
We calculate large mass diphoton exclusive photoproduction in the framework of collinear QCD factorization at next to leading order in {\alpha}s and at leading twist. Collinear divergences of the coefficient function are absorbed by the…
We present a simple parameterization of the two-photon exchange amplitude in elastic electron-proton scattering, suitable for fast numerical evaluation.
We describe the present status of the pion distribution amplitude as originated from two sources: (i) a nonperturbative approach, based on QCD sum rules with nonlocal condensates, and (ii) a NLO QCD analysis of the CLEO data on…
The production of charged pion pairs via multiphoton absorption from an intense X-ray laser wave colliding with an ultrarelativistic proton beam is studied. Our calculations include the contributions from both the electromagnetic and…
We present complete analytical ${\mathcal O}(\epsilon^2)$ results on the one-loop amplitudes relevant for the NNLO quark-parton model description of the hadroproduction of heavy quarks as given by the so-called loop-by-loop contributions.…
Spin-observables in pseudoscalar meson photoproduction is discussed. This work is complementary to the earlier works on this topic. Here, the reaction amplitude is expressed in Pauli-spin basis which allows to calculate all the observables…
We derive and apply the finite energy sum rules to pion photoproduction. We evaluate the low energy part of the sum rules using several state-of-the-art models. We show how the differences in the low energy side of the sum rules might…
We discuss the elastic photo- and leptoproduction of rho^0-mesons from nucleons at Q^2 < 1 GeV^2 as studied in recent experiments at HERA and FNAL. We find that the mass distribution of the measured \pi^+\pi^- pairs is determined to a large…
Strong collinear divergences, although regularized by a thermal mass, result in a breakdown of the standard hard thermal loop expansion in the calculation of the production rate of photons by a plasma of quarks and gluons using thermal…
We use general relations between the Transition Distribution Amplitudes (TDAs), entering the description of the p -> pi0 transition, and the proton Distribution Amplitudes (DAs) in the soft-pion limit to estimate the size of the amplitude…
In this talk we cover several issues concerning pion production. The first one is the p p ----> p p pi^0 reaction where an alternative explanation based on the off shell extrapolation of the pi N amplitude is offered. A recent model for the…