Springer Berlin HeidelbergBerlin/HeidelbergSpringer1313010.1007/13130.1029-84791029-847932745009Journal of High Energy PhysicsJ. High Energ. Phys.PhysicsElementary Particles, Quantum Field TheoryQuantum Field Theories, String TheoryClassical and Quantum Gravitation, Relativity TheoryQuantum PhysicsPhysics and Astronomy2020202012551612020823202052020The Author(s)2020130641911.1315010.1007/JHEP05(2020)126126126Nucleon axial structure from lattice QCDRegular Article - Theoretical Physics15920205262020110202031320204242020526The Author(s)2020131302020202055The RQCD collaborationGunnarS.Baligunnar.bali@ur.deLorenzoBarcalorenzo1.barca@ur.deSaraCollinssara.collins@ur.deMichaelGrubermichael1.gruber@ur.deMariusLöfflermarius.loeffler@ur.deAndreasSchäferandreas.schaefer@ur.deWolfgangSöldnerwolfgang.soeldner@ur.dePhilippWeinphilipp.wein@ur.deSimonWeishäuplsimon.weishaeupl@ur.deThomasWurmthomas.wurm@ur.degrid.7727.50000 0001 2190 5763Institut für Theoretische PhysikUniversität RegensburgUniversitätsstraße 31D-93040RegensburgGermanygrid.22401.350000 0004 0502 9283Department of Theoretical PhysicsTata Institute of Fundamental ResearchHomi Bhabha RoadMumbai400005IndiaAbstractWe present a new analysis method that allows one to understand and model excited state contributions in observables that are dominated by a pion pole. We apply this method to extract axial and (induced) pseudoscalar nucleon isovector form factors, which satisfy the constraints due to the partial conservation of the axial current up to expected discretization effects. Effective field theory predicts that the leading contribution to the (induced) pseudoscalar form factor originates from an exchange of a virtual pion, and thus exhibits pion pole dominance. Using our new method, we can recover this behavior directly from lattice data. The numerical analysis is based on a large set of ensembles generated by the CLS effort, including physical pion masses, large volumes (with up to 963 × 192 sites and Lmπ = 6.4), and lattice spacings down to 0.039 fm, which allows us to take all the relevant limits. We find that some observables are much more sensitive to the choice of parametrization of the form factors than others. On the one hand, the z-expansion leads to significantly smaller values for the axial dipole mass than the dipole ansatz (${M}_{A}^{z-\mathit{exp}}$$$ {M}_A^{z-\mathit{\exp}} $$ = 1.02(10) GeV versus ${M}_{A}^{\text{dipole}}$$$ {M}_A^{\mathrm{dipole}} $$ = 1.31(8) GeV). On the other hand, we find that the result for the induced pseudoscalar coupling at the muon capture point is almost independent of the choice of parametrization (${g}_{P}^{\ast z-\mathit{exp}}$$$ {g}_P^{\ast z-\mathit{\exp}} $$ = 8.68(45) and ${g}_{P}^{\ast \text{dipole}}$$$ {g}_P^{\ast \mathrm{dipole}} $$ = 8.30(24)), and is in good agreement with both, chiral perturbation theory predictions and experimental measurement via ordinary muon capture. We also determine the axial coupling constant gA.KeywordsLattice QCDNeutrino PhysicsNonperturbative EffectsArXiv ePrint: 1911.13150Electronic supplementary materialThe online version of this article (https://doi.org/10.1007/JHEP05(2020)126) contains supplementary material, which is available to authorized users.