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

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 $G_{\mathrm{A}}(Q^2)$ is at the 5 percent level for source-sink separations of 2 fm and shows almost no dependence on the momentum transfer $Q^2$. In contrast, for the induced pseudo scalar form factor $G_{\mathrm{P}}(Q^2)$ the nucleon-pion-state contribution shows a rather strong dependence on $Q^2$ and leads to a 10 to 40 percent underestimation of $G_{\mathrm{P}}(Q^2)$ 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.

7 pages, 3 figures. Talk given at Lattice 2018

References in corpus (3)

• Iso-vector axial form factors of the nucleon in two-flavour lattice QCD
• Nucleon form factors on a large volume lattice near the physical point in 2+1 flavor QCD
• Multi-hadron-state contamination in nucleon observables from chiral perturbation theory

Cited by in corpus (5)

• Nucleon form factors on a large volume lattice near the physical point in 2+1 flavor QCD
• $N\pi$-state contamination in lattice calculations of the nucleon axial form factors
• Solving the PCAC puzzle for nucleon axial and pseudoscalar form factors
• Hints and challenges in heavy flavor physics
• A new method for suppressing excited-state contaminations on the nucleon form factors