The light-quark mass dependence of the nucleon axial charge

Abstract

The light-quark mass dependence of the nucleon axial isovector charge (gA) has been analysed up to NNLO, O(p4), in relativistic chiral perturbation theory using extended-on-mass-shell renormalization, without and with explicit Delta(1232) degrees of freedom. In the Delta-less case at this order, the gA(Mpi) dependence of lattice QCD simulations cannot be reproduced using low energy constants extracted from pion-nucleon phenomenology. A good description of these LQCD data is only accomplished in the theory with Delta. From this fit we obtain gA(Mpiphys)=1.260(12) close to the experimental results and d16= -0.88(88) GeV-2 in agreement with pi N-> pi pi N. The sizeable errors are of theoretical origin, reflecting the difference between O(p3) and O(p4) at large Mpi.