Abstract
The axial charge of the nucleon gA and the pion decay constant fπ are computed in two-flavor lattice QCD. The simulations are carried out on lattices of various volumes and lattice spacings. Results are reported for pion masses as low as mπ=130 MeV. Both quantities, gA and fπ, suffer from large finite size effects, which to leading order ChEFT and ChPT turn out to be identical. By considering the naturally renormalized ratio gA/fπ, we observe a universal behavior as a function of decreasing quark mass. From extrapolating the ratio to the physical point, we find gAR=1.29(5)(3), using the physical value of fπ as input and r0=0.50(1) to set the scale. In a subsequent calculation we attempt to extrapolate gA and fπ separately to the infinite volume. Both volume and quark mass dependencies of gA and fπ are found to be well described by ChEFT and ChPT. We find at the physical point gAR=1.24(4) and fπR=89.6(1.1)(1.8) MeV. Both sets of results are in good agreement with experiment. As a by-product we obtain the low-energy constant l¯4=4.2(1).
Highlights
The axial charge g A of the nucleon is a fundamental measure of nucleon structure
In Appendix A we show, based on predictions of ChEFT and ChPT adapted to the finite volume, that the leading corrections to g A and fπ are identical and cancel in the ratio g A / fπ
The renormalized axial charge g in the infinite volume plotted against m2π (∞), together with the experimental value g A = 1.27 (×)
Summary
The axial charge g A of the nucleon is a fundamental measure of nucleon structure. While g A has been known accurately for many years from neutron β decays, a calculation of g A from first principles still presents a significant challenge. Though it is standard practice nowadays to compute the renormalization constant nonperturbatively (see, for example, [6,7]), some scope of uncertainty remains [8] Another common feature is that g A and fπ seem to be affected by large finite size corrections, in particular at small pion masses, which to leading order ChEFT and ChPT [9,10,11] appear to be the same in both cases. The calculations are done with two flavors of nonperturbatively O (a) improved Wilson fermions and Wilson plaquette action [13], including simulations at virtually physical pion mass and on a variety of lattice volumes. This allows for a separate extrapolation of both g A and fπ to the infinite volume and the physical point
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
