| Sumario: | The light-quark mass dependence of the nucleon axial isovector charge (gA) has been studied up to next-to-next-to-leading order, O(p4), in relativistic chiral perturbation theory using extended-on-mass-shell renormalization, without and with explicit Δ(1232) degrees of freedom. We show that in the Δ-less case, at this order, the flat trend of gA(Mπ) exhibited by state-of-the-art lattice QCD (LQCD) results cannot be reproduced using low energy constants extracted from pion-nucleon elastic and inelastic scattering. A satisfactory description of these LQCD data is only achieved in the theory with Δ. From this fit, we report gA(Mπ(phys))=1.260±0.012, close to the experimental result, and d16=-0.88±0.88 GeV-2, in agreement with its empirical value. The large uncertainties are of theoretical origin, reflecting the difference between O(p3) and O(p4) that still persists at large Mπ in presence of the Δ.
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