Spin polarisability of the nucleon at NLO in the chiral expansion

TL;DR

This paper calculates the next-to-leading order contribution to the nucleon's spin polarisability within heavy-baryon chiral perturbation theory, revealing significant corrections that challenge precise predictions.

Contribution

It provides the first NLO calculation of the nucleon spin polarisability in chiral perturbation theory, highlighting the importance of higher-order effects.

Findings

NLO contribution is nearly twice the leading order in magnitude.

The sign of the NLO correction is opposite to the leading term.

Current theoretical predictions for the spin polarisability are unreliable due to large corrections.

Abstract

We present a calculation of the fourth-order (NLO) contribution to spin-dependent forward Compton scattering in heavy-baryon chiral perturbation theory. No low-energy constants, except for the anomalous magnetic moments of the nucleon, enter at this order. The fourth-order piece of the spin polarisability of the proton turns out to be almost twice the size of the leading piece, with the opposite sign. This leads to the conclusion that no prediction can currently be made for this quantity.