2025/05/11 by Aoki, Yasumichi, Ishikawa, Ken-Ichi, Kuramashi, Yoshinobu +6 · 2 citations
#FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2505.06854
We performed a precise calculation of physical quantities related to the axial structure of the nucleon using 2+1 flavor lattice QCD gauge configuration (PACS10 configuration) generated at the physical point with lattice volume larger than (10 fm)4 by the PACS Collaboration. The nucleon matrix element of the axial-vector current has two types of the nucleon form factors, the axial-vector (FA) form factor and the induced pseudoscalar (FP) form factor. Recently lattice QCD simulations have succeeded in reproducing the experimental value of the axial-vector coupling, gA, determined from FA(q2) at zero momentum transfer q2=0, at a percent level of statistical accuracy. However, the FP form factor so far has not reproduced the experimental values well due to strong πN excited-state contamination. Therefore, we proposed a simple subtraction method for removing the so-called leading πN-state contribution, and succeeded in reproducing the values obtained by two experiments of muon capture on the proton and pion electro-production for FP(q2). The novel approach can also be applied to the nucleon pseudoscalar matrix element to determine the pseudoscalar (GP) form factor with the help of the axial Ward-Takahashi identity. The resulting form factors, FP(q2) and GP(q2), are in good agreement with the prediction of the pion-pole dominance model. In the new analysis, the induced pseudoscalar coupling gP^∗ and the pion-nucleon coupling gπNN can be evaluated with a few percent accuracy including systematic uncertainties using existing data calculated at two lattice spacings.