Germar Knochlein

Structure analysis of the virtual Compton scattering amplitude at low energies

Published in: Phys. Rev. C 57 (1998) 941-952 Citing articles (CrossRef) citations recorded in [Science Citation Index] Abstract: We analyze virtual Compton scattering (VCS) off the nucleon at low energies in a covariant, model-independent formalism. We define a set of invariant functions which, for the structure-dependent part of the VCS amplitude, is free of poles and kinematical zeros. The covariant treatment naturally allows to implement the constraints due to Lorentz and gauge invariance, crossing symmetry, and the discrete symmetries. In particular, when applied to the photon electroproduction reaction, charge-conjugation symmetry in combination with nucleon crossing generates four relations among the ten originally proposed generalized polarizabilities of the nucleon. We perform a 1/M expansion of the VCS amplitude near the real-photon point and show how the generalized polarizabilities can be extracted from such an expansion. Finally, we discuss the real-photon limit including the spin-independent as well as the spin-dependent polarizabilities.

Generalized polarizabilities and the spin-averaged amplitude in virtual Compton scattering off the nucleon

We discuss the low-energy behavior of the spin-averaged amplitude of virtual Compton scattering (VCS) off a nucleon. Based on gauge invariance, Lorentz invariance and the discrete symmetries, it is shown that to first order in the frequency of the final real photon only two generalized polarizabilities appear. Different low-energy expansion schemes are discussed and put into perspective.

Virtual Compton scattering off the nucleon in chiral perturbation theory

We investigate the spin-independent part of the virtual Compton scattering (VCS) amplitude off the nucleon within the framework of chiral perturbation theory. We perform a consistent calculation to third order in external momenta according to Weinberg`s power counting. With this calculation we can determine the second- and fourth-order structure-dependent coefficients of the general low-energy expansion of the spin-averaged VCS amplitude based on gauge invariance, crossing symmetry, and the discrete symmetries. We discuss the kinematical regime to which our calculation can be applied and compare our expansion with the multipole expansion by Guichon, Liu, and Thomas. We establish the connection of our calculation with the generalized polarizabilities of the nucleon where it is possible. {copyright} {ital 1997} {ital The American Physical Society}

Low-energy and low-momentum representation of the virtual Compton scattering amplitude

We perform an expansion of the virtual Compton scattering amplitude for low energies and low momenta and show that this expansion covers the transition from the regime to be investigated in the scheduled photon electroproduction experiments to the real Compton scattering regime. We discuss the relation of the generalized polarizabilities of virtual Compton scattering to the polarizabilities of real Compton scattering.

Rare decay eta --> pi pi gamma gamma in chiral perturbation theory.

We investigate the rare radiative {eta} decay modes {eta}{r_arrow}{pi}{sup +}{pi}{sup {minus}}{gamma}{gamma} and {eta}{r_arrow}{pi}{sup 0}{pi}{sup 0}{gamma}{gamma} within the framework of chiral perturbation theory at {ital O}({ital p}{sup 4}). We present photon spectra and partial decay rates for both processes as well as a Dalitz contour plot for the charged decay. {copyright} {ital 1996 The American Physical Society.}

The anomalous decay η → ππγγ☆

We investigate the rare radiative eta decay modes eta -> pi+ pi- gamma gamma and eta -> pi0 pi0 gamma gamma within the framework of chiral lagrangians at o(p^4) and present photon spectra for both processes.

Generalized polarizabilities and the chiral structure of the nucleon

Abstract We discuss the virtual Compton scattering reaction e − p → e − pγ at low energies. We present results for the generalized polarizabilities of the nucleon obtained in heavy baryon chiral perturbation theory at O ( p 3 ).