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Nucleon axial and pseudoscalar form factors using twisted-mass fermion ensembles at the physical point
Alexandrou, Constantia Bacchio, Simone Constantinou, Martha Finkenrath, Jacob Frezzotti, Roberto Kostrzewa, Bartosz Koutsou, Giannis Spanoudes, Gregoris Urbach, Carsten
Alexandrou, Constantia
Bacchio, Simone
Constantinou, Martha
Finkenrath, Jacob
Frezzotti, Roberto
Kostrzewa, Bartosz
Koutsou, Giannis
Spanoudes, Gregoris
Urbach, Carsten
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2024-02-05
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Physics
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https://doi.org/10.1103/physrevd.109.034503
Abstract
We compute the nucleon axial and pseudoscalar form factors using three 𝑁𝑓 =2 +1 +1 twisted-mass fermion ensembles with all quark masses tuned to approximately their physical values. The values of the lattice spacings of these three physical point ensembles are 0.080, 0.068, and 0.057 fm and spatial sizes 5.1, 5.44, and 5.47 fm, respectively, yielding 𝑚𝜋𝐿 >3.6. Convergence to the ground-state matrix elements is assessed using multistate fits. We study the momentum dependence of the three form factors and check the partially conserved axial-vector current (PCAC) hypothesis and the pion pole dominance (PPD). We show that in the continuum limit, the PCAC and PPD relations are satisfied. We also show that the Goldberger-Treimann relation is approximately fulfilled and determine the Goldberger-Treiman discrepancy. Our final results are 𝑔𝐴 =1.245(28)(14) for the nucleon axial charge, ⟨𝑟2𝐴⟩ =0.339(48)(06)fm2 for the axial radius, 𝑔𝜋𝑁𝑁 ≡ lim𝑄2→−𝑚2𝜋𝐺𝜋𝑁𝑁(𝑄2) =13.25(67)(69) for the pion-nucleon coupling constant, and 𝐺𝑃(0.88𝑚2𝜇) ≡𝑔*𝑃 =8.99(39)(49) for the induced pseudoscalar form factor at the muon capture point.
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Physical Review D, Vol. 109, Iss. 3
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