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Can we determine the exact size of the nucleon?: A comprehensive study of different radii

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arxiv 2503.08847 v3 pith:OGFL2AXO submitted 2025-03-11 hep-ph hep-exhep-lat

classification hep-phhep-exhep-lat
keywords nucleonradiiradiusstructurechargeinternalsizecomprehensive
verification ladder T0 review T1 audit T2 compute T3 formal
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The concept of nucleon radii plays a central role in our understanding of the internal structure of protons and neutrons, providing critical insights into the non-perturbative regime of quantum chromodynamics (QCD). While the charge radius is often interpreted as the ``size" of the nucleon, this interpretation is an oversimplification that overlooks the multifaceted nature of nucleon structure. This paper provides a comprehensive overview of the different nucleon radii, including the charge and magnetic radii, the axial radius, and the emerging concepts of mechanical and mass radii. We discuss the definitions as well as the experimental, theoretical and phenomenological determinations of these radii, highlighting their distinct physical origins and implications. By synthesizing recent experimental results and theoretical advancements, we emphasize that each radius reflects a specific aspect of the nucleon's internal structure, such as its electric charge distribution, magnetic properties, weak interactions, or internal mechanical stress. In particular, we address the common but misleading interpretation of the proton radius as a simple measure of its size, underscoring the nuanced and context-dependent nature of nucleon radii. Through this exploration, we aim to clarify the roles of these radii in characterizing nucleon structure and to identify open questions that remain to be addressed. This work contributes to a deeper understanding of the nucleon and its significance in the broader context of particle and nuclear physics.

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Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Mass radius and D-term of atomic nuclei in relativistic mean field theory

    nucl-th 2026-05 unverdicted novelty 7.0 of 10

    D-term of nuclei exhibits kinks at magic neutron numbers, showing strong sensitivity of mechanical properties to shell structure.

  2. Extraction of the nucleon axial form factor from Lattice QCD using NNLO chiral perturbation theory

    hep-ph 2026-06 conditional novelty 6.0 of 10

    A global NNLO chiral-perturbation-theory fit with explicit Delta to lattice-QCD axial form factors gives g_A = 1.257 ± 0.011 and r_A² = 0.312 ± 0.037 fm².

  3. The Nucleon Axial Form Factor from Elementary Target Data

    hep-ex 2025-12 conditional novelty 6.0 of 10

    The nucleon axial form factor from hydrogen and lattice-QCD data falls more slowly with Q² than deuterium-based fits, indicating deuterium extractions are biased low.

  4. Implications of exclusive photon leptoproduction measurements for the proton charge-radius puzzle

    hep-ph 2026-07 conditional novelty 5.0 of 10

    After excluding or cutting low-|t| CLAS 2018 data, BH-dominated EP measurements yield a proton charge radius smaller than the PDG average and consistent with PRad and muonic hydrogen.

  5. Gravitational form factors of the nucleon in the Skyrme model based on scale-invariant chiral perturbation theory

    hep-ph 2025-07 conditional novelty 5.0 of 10

    A Skyrme model with a dilaton field attributes the proton's negative internal pressure and confining force to the gluonic scale anomaly, and reproduces the lattice QCD D(t) form factor.

  6. Extraction of the nucleon axial form factor from Lattice QCD using NNLO chiral perturbation theory

    hep-ph 2026-06 unverdicted novelty 4.0 of 10

    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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