Nothing anomalous about two-loop HBCPT: consistency with the LET for spin-dependent Compton scattering

TL;DR

This paper demonstrates that two-loop heavy-baryon chiral perturbation theory (HBCPT) results for spin-dependent Compton scattering are consistent with low energy theorems, confirming the theory's validity at this order.

Contribution

It provides the first consistency check of two-loop HBCPT against low energy theorems for spin-dependent Compton scattering.

Findings

Sum of two-loop processes vanishes as photon energy approaches zero.

Results confirm the validity of two-loop HBCPT for this process.

Supports the theoretical framework's consistency with established low energy theorems.

Abstract

The leading order contributions of processes involving anomalous pion-photon vertices to forward spin-dependent Compton scattering from nucleons are considered in heavy-baryon chiral perturbation theory. These all involve the exchange of three pions between one or two photons and the nucleon, and hence are two-loop processes. We find that the sum of these processes vanishes in the manner predicted by the low energy theorem of Low, Gell-Mann and Goldberger as the photon energy goes to zero. This provides the first consistency test of two-loop HBCPT.