Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory. II. Spin polarizabilities and moments of polarized structure functions

Abstract

We examine the polarized doubly-virtual Compton scattering (VVCS) off the nucleon using chiral perturbation theory ( χ PT ). The polarized VVCS contains a wealth of information on the spin structure of the nucleon which is relevant to the calculation of the two-photon-exchange effects in atomic spectroscopy and electron scattering. We report on a complete next-to-leading-order calculation of the polarized VVCS amplitudes S 1 ( ν , Q 2 ) and S 2 ( ν , Q 2 ) , and the corresponding polarized spin structure functions g 1 ( x , Q 2 ) and g 2 ( x , Q 2 ) . Our results for the moments of polarized structure functions, partially related to different spin polarizabilities, are compared to other theoretical predictions and “data-driven” evaluations, as well as to the recent Jefferson Lab measurements. By expanding the results in powers of the inverse nucleon mass, we reproduce the known “heavy-baryon” expressions. This serves as a check of our calculation, as well as demonstrates the differences between the manifestly Lorentz-invariant baryon χ PT and heavy-baryon frameworks.