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Given that each quark flavor has a particular electric charge (i.e., either +2/3 or -1/3): how do these charges effect the internal dynamics of hadrons? Do the attractive and repulsive effects of electromagnetism play a meaningful role in hadron dynamics (e.g., how protons (uud) and neutrons (udd) remain relatively stable), or does the strength of the strong force completely dominate these dynamics?

In other words, what is the overall role and effect of electromagnetism within (i.e., within the interior of, rather than external to) hadrons?

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    $\begingroup$ Hint: Isospin symmetry. $\endgroup$
    – Qmechanic ♦
    Commented Nov 8, 2023 at 7:09
  • $\begingroup$ The charge radius of the neutron is negative…. $\endgroup$
    – Cosmas Zachos
    Commented Nov 8, 2023 at 12:13

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As a rough order of magnitude estimate you may consider the ratio $\frac{m_n-m_p}{m_p} \simeq 0.0013$, i.e. electromagnetism and the $u,d$ quark mass difference affect this ratio only at the per mille level.

An even better example is the ratio $\frac{M_\pi^\pm-M_\pi^0}{M_\pi}\simeq 0.03$, being practically a purely electromagnetic effect as contributions originating from the $u,d$ quark mass difference are heavily suppressed in that case.

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  • $\begingroup$ According to physics.stackexchange.com/a/34262/219989, " it's mostly the fact that the down quark is heavier than the up quark that makes the neutron heavier than the proton" - not the different charge. $\endgroup$
    – Nadav Har'El
    Commented Nov 8, 2023 at 7:53
  • $\begingroup$ @NadavHar'El I have now included now both effects in my answer. $\endgroup$
    – Hyperon
    Commented Nov 8, 2023 at 8:00
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    $\begingroup$ For a long time, QCD simulations simply ignored the electromagnetic interaction as being too small a perturbation. A first estimate by considering the nuclei as a roughly constant charge density liquid drop provides a great averaged contribution. Only in the recent decade have people started to add the perturbation of actual QED interaction to the behaviour of quarks. $\endgroup$
    – naturallyInconsistent
    Commented Nov 8, 2023 at 17:54

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