Inferring the breakdown scales of the chiral expansions for gA and mN

Journal article, 2026

We apply Bayesian inference to the order-by-order chiral perturbation theory (xPT) expansions for the axial-vector coupling constant gA and the nucleon mass mN, and thereby infer the scales at which xPT breaks down for these two observables. Using a pointwise Bayesian analysis, we find that the inferred breakdown scales are notably different for the two observables. For the chiral expansion of gA, we obtain 251+20-50 MeV and 211+20-30 MeV using two distinct sets of low-energy constants, while for the chiral expansion of mN we infer a significantly larger breakdown scale of 491+60-90 MeV.