Nucleon-pion-state contamination in lattice calculations of the axial form factors of the nucleon

2018/08/27 by Bar, Oliver
#FOS: Physical sciences #High Energy Physics - Lattice (hep-lat)

paper · doi:10.48550/arxiv.1808.08738

Abstract

The nucleon-pion-state contribution to QCD two- and three-point functions used in the calculation of the axial form factors of the nucleon are studied in chiral perturbation theory. For physically small quark masses the nucleon-pion states are expected to dominante the excited-state contamination at large euclidean time separations. To leading order in chiral perturbation theory the results depend on two experimentally well-known low-energy constants only and the nucleon-pion-state contribution can be reliably estimated. The nucleon-pion-state contribution to the axial form factor G_{\rm A}(Q²) is at the 5 percent level for source-sink separations of 2 fm and shows almost no dependence on the momentum transfer Q². In contrast, for the induced pseudo scalar form factor G_{\rm P}(Q²) the nucleon-pion-state contribution shows a rather strong dependence on Q² and leads to a 10 to 40 percent underestimation of G_{\rm P}(Q²) at small momentum transfers. Applying the ChPT results to recent lattice data generated by the PACS collaboration we find agreement with experimental data and the predictions of the pion-pole dominance model.

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