Search results for "Quantum electrodynamics."
showing 10 items of 797 documents
Gerasimov-Drell-Hearn sum rule and related integrals
2001
The spin structure of the nucleon resonance region is analyzed on the basis of our phenomenological model MAID. Predictions are given for the Gerasimov-Drell-Hearn sum rule as well as generalized integrals over spin structure functions. The dependence of these integrals on momentum transfer is studied and rigorous relationships between various definitions of generalized Gerasimov-Drell-Hearn integrals and spin polarizabilities are derived. These results are compared to the predictions of chiral perturbation theory and phenomenological models.
Reply to “Comment on ‘Polarizability of the pion: No conflict between dispersion theory and chiral perturbation theory’”
2009
We show that the alleged discrepancies between chiral perturbation theory (ChPT) and dispersion theory, reported for the polarizability of the pion by Fil'kov and Kashevarov [Phys. Rev. C 72, 035211 (2005)], result from applying dispersion theory to nonanalytic functions.
The polarizability of the pion: no conflict between dispersion theory and chiral perturbation theory
2008
Recent attempts to determine the pion polarizability by dispersion relations yield values that disagree with the predictions of chiral perturbation theory. These dispersion relations are based on specific forms for the absorptive part of the Compton amplitudes. The analytic properties of these forms are examined, and the strong enhancement of intermediate-meson contributions is shown to be connected with spurious singularities. If the basic requirements of dispersion relations are taken into account, the results of dispersion theory and effective field theory are not inconsistent.
〈VAP〉 Green function in the resonance region
2004
Abstract We analyze the 〈 V A P 〉 three-point function of vector, axial-vector and pseudoscalar currents. In the spirit of large N C , a resonance dominated Green function is confronted with the leading high-energy behaviour from the operator product expansion. The matching is shown to be fully compatible with a chiral resonance Lagrangian and it allows to determine some of the chiral low-energy constants of O ( p 6 ) .
Statistical quantities in particle collisions
1972
Abstract Statistical quantities for particle collisions are defined using the analogy between the phase-space integral in multiparticle collisions and that in relativistic quantum statistical mechanics. The analogs of thermodynamic quantities are computed for the uncorrelated jet model. A relativistic derivation for the mass spectrum of hadrons is given and thermodynamic quantities are calculated for a system with this spectrum.
Quasi-particle and plasmaron properties in the electron gas
1972
The self-energy function of the degenerate electron gas is studied in an approximation which uses the dielectric function proposed by Singwi, Tosi, Land and Sjolander, and neglects the corresponding vertex corrections. Two contributions to the self-energy are distinguished which arise from the plasmon pole and the particle-hole continuum respectively. Comparison of the results is made with the analogous approximation to the self-energy which uses the RPA dielectric function, and with a further, simplified approximation. Subsequently the properties of the usual quasi-particle and of the plasmaron are calculated. Nummerically, the most significant effect found is a 25% reduction of the plasma…
Influence of Coulomb distortion on polarization observables in elastic electromagnetic lepton hadron scattering at low energies
2011
The formal expression for the most general polarization observable in elastic electromagnetic lepton hadron scattering at low energies is derived for the nonrelativistic regime. For the explicit evaluation the influence of Coulomb distortion on various polarization observables is calculated in a distorted wave Born approximation. Besides the hyperfine interaction also the spin-orbit interactions of lepton and hadron are included. For like charges the Coulomb repulsion reduces strongly the size of polarization observables compared to the plane wave Born approximation whereas for opposite charges the Coulomb attraction leads to a substantial increase of these observables for hadron lab kineti…
A model study on the nuclear photoeffect
1977
In a simple model of a spinless particle moving in a finite square well potential influences of final state Born approximation and of various approximations in the electromagnetic operators on photoabsorption differential, total and integrated cross sections are investigated. While the Born approximation is very poor in all respects, the long wave length approximation turns out to be the best and reproduces the total cross section quite well. However, appreciable deviations occur in the differential cross section at intermediate energies. The integrated cross section slightly exceeds the classical sum rule resulting from nonanalyticity of the forward compton scattering amplitude, as is disc…
Final State Interaction Effects in 3He(e ,e'p)
2003
Abstract Asymmetries in quasi-elastic 3 He ( e → , e ′ p ) have been measured at a momentum transfer of 0.67 (GeV/ c ) 2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3 He -ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.
Inclusive electron scattering off 4He
2007
Inclusive electron scattering off 4He is investigated for low and medium energy and momentum transfers. The final state interaction, given by the simple semirealistic Malfliet-Tjon potential, is treated rigorously applying the Lorentz Integral Transform (LIT) method. Besides the nonrelativistic one-body current a consistent meson exchange current is constructed and implemented. Results are presented for both longitudinal and transverse response functions at various momentum transfers. Good agreement with experimental data is found for the longitudinal response function, while some strength is missing in the transverse response function on the low-energy side of the quasi-elastic peak.