In a finite box the axial-vector current matrix element between two nucleons requires a larger set of form factors than the usual two employed in infinite volume; the complete one-loop expressions are derived in SU(2) chiral EFT with Delta degrees of freedom.
Extraction of nucleon axial charge and radius from lattice QCD results using baryon chiral perturbation theory
2 Pith papers cite this work. Polarity classification is still indexing.
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abstract
We calculate the nucleon axial form factor up to the leading one-loop order in a covariant chiral effective field theory with the $\Delta(1232)$ resonance as an explicit degree of freedom. We fit the axial form factor to the latest lattice QCD data and pin down the relevant low-energy constants. The lattice QCD data, for various pion masses below $400$ MeV, can be well described up to a momentum transfer of $\sim 0.6$ GeV. The $\Delta(1232)$ loops contribute significantly to this agreement. Furthermore, we extract the axial charge and radius based on the fitted values of the low energy constants. The results are: $g_A=1.237(74)$ and $\langle r_A^2\rangle =0.263(38)~{\rm fm}^2$. The obtained coupling $g_A$ is consistent with the experimental value if the uncertainty is taken into account. The axial radius is below but in agreement with the recent extraction from neutrino quasi-elastic scattering data on deuterium, which has large error bars. Up to our current working accuracy, $r_A$ is predicted only at leading order, i.e., one-loop level. A more precise determination might need terms of $\mathcal{O}(p^5)$.
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NNLO ChPT with explicit Delta fits lattice data to extract g_A = 1.257 ± 0.011 and axial radius squared 0.312 ± 0.037 fm² at the physical point.
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Decomposition of the axial-vector current in a finite box
In a finite box the axial-vector current matrix element between two nucleons requires a larger set of form factors than the usual two employed in infinite volume; the complete one-loop expressions are derived in SU(2) chiral EFT with Delta degrees of freedom.
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Extraction of the nucleon axial form factor from Lattice QCD using NNLO chiral perturbation theory
NNLO ChPT with explicit Delta fits lattice data to extract g_A = 1.257 ± 0.011 and axial radius squared 0.312 ± 0.037 fm² at the physical point.