Syndrome de Segawa : étude clinique de 2 familles tunisiennes

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=130MeV. 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).