Isovector Axial Charge and Form Factors of Nucleons from Lattice QCD

2024/01/29 by Rajan Gupta, Gupta, Rajan · 2 citations
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Nuclear Theory (nucl-th) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions

paper · pdf · doi:10.48550/arxiv.2401.16614

openalex publication_date 2024/01/29 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30

Abstract

I present an overview of the calculations of the isovector axial vector form factor of the nucleon, G_A(Q²), using lattice QCD. Based on a comparison of results from various collaborations, a case is made that lattice results are now consistent within 10%. A similar level of uncertainty is found also in the axial charge g_A^u-d, the mean squared axial charge radius, ⟨ r_A² ⟩, the induced pseudoscalar charge g_P^∗, and the pion-nucleon coupling g_πNN. These lattice results for G_A(Q²) are already compatible with those obtained from the recent MINERνA experiment but lie 2-3σ higher than the phenomenological extraction from the old ν-deuterium bubble chamber scattering data for Q² > 0.3~GeV². Fits to our data show that the dipole ansatz does not have enough parameters to parameterize the form factor over the range 0 ≤ Q² ≤ 1~GeV², whereas even a z² truncation of the z-expansion or a low order Padé are sufficient. Looking ahead, lattice QCD calculations will provide increasingly precise results over the range 0 ≤ Q² \lesssim 1~GeV², and MINERνA-like experiments will extend the range to Q² ∼ 2~GeV² or higher. To increase precision of lattice data to the percent level, new developments are needed to address two related issues: the exponentially falling signal-to-noise ratio in all nucleon correlation functions and removing excited state contributions. Nevertheless, even with the current methodology, significant reduction in errors is expected over the next few years with higher statistics data on more ensembles closer to the physical point.

Cited by

• Pseudoscalar meson dominance, the pion-nucleon coupling constant and the Goldberger-Treiman discrepancy
• Method for high-precision determination of the nucleon axial structure using lattice QCD: Removing πN-state contamination

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• Investigating the axial structure of the nucleon based on large-volume lattice QCD at the physical point