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We examine the polarized doubly-virtual Compton scattering (VVCS) off thenucleon using chiral perturbation theory ($\chi$PT). The polarized VVCScontains a wealth of information on the spin structure of the nucleon which isrelevant to the calculation of the two-photon-exchange effects in atomicspectroscopy and electron scattering. We report on a completenext-to-leading-order (NLO) calculation of the polarized VVCS amplitudes$S_1(\nu, Q^2)$ and $S_2(\nu, Q^2)$, and the corresponding polarized spinstructure functions $g_1(x, Q^2)$ and $g_2(x,Q^2)$. Our results for the momentsof polarized structure functions, partially related to different spinpolarizabilities, 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 reproducethe known "heavy-baryon" expressions. This serves as a check of ourcalculation, as well as demonstrates the differences between the manifestlyLorentz-invariant baryon $\chi$PT (B$\chi$PT) and heavy-baryon (HB$\chi$PT)frameworks.

physical review. d/physical review. d.

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