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Excited-state contamination is one of the dominant uncertainties in latticecalculations of the nucleon axial-charge, $g_A$. Recently published results inleading-order chiral perturbation theory (ChPT) predict the excited-statecontamination to be independent of the nucleon interpolator and positive.However, empirical results from numerical lattice calculations show negativecontamination (downward curvature), indicating that present-day calculationsare not in the regime where the leading-order ChPT predictions apply. In thispaper we show that, under plausible assumptions, one can reproduce the behaviorof lattice correlators by taking into account final-state $N \pi$ interactions,in particular the effect of the Roper resonance, and by postulating a signchange in the infinite-volume $N \to N \pi$ axial-vector transition amplitude.

On the effect of excited states in lattice calculations of the nucleon axial charge