Imagine a positive and negative pion, their only interaction between each other would be due to electromagnetism and the weak force, right? It is not like these two pions can form neutral pions due to the strong force. Otherwise it would mean the pions have emitted "gluonic" radiation due to the difference in binding energies which is obviously impossible.

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    $\begingroup$ In some literature the “fictitious sigma meson” is treated as a two-pion molecule. See this related question for a more nuanced and contemporary view. $\endgroup$
    – rob
    Sep 12, 2022 at 19:23
  • $\begingroup$ This was almost exactly what I was going for. Thank you! $\endgroup$ Sep 12, 2022 at 19:25
  • $\begingroup$ Note the QCD in the answer, that is the strong force, that is always there for the quarks that make up the resonance, so your "only interactions" is not correct. $\endgroup$
    – anna v
    Sep 13, 2022 at 4:22

1 Answer 1


Do pions not interact with other pions via the strong force

Pions are bound states of quark anti quark that have a small lifetime, so pion pion scattering experiments are note easy to design. The forces that would enter in any calculation are the strong, the weak, and the electromagnetic, the strong by definition being the strongest. The hypothesis that the only forces are the weak and electromagnetic is wrong.


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