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Particles that transform non-trivially under color $SU(3)$ interact via strong nuclear force. However, neutrons and protons, despite being color singlets, interact via the strong force. How do we account for this from QCD?

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    $\begingroup$ Search term: residual strong force. $\endgroup$
    – rob
    Aug 14, 2023 at 16:44
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    $\begingroup$ How do atoms interact despite their overall neutrality? $\endgroup$
    – Jon Custer
    Aug 14, 2023 at 16:48
  • $\begingroup$ @JonCuster They can interact via dipole-dipole interaction. for example. What is the analog here? $\endgroup$ Aug 14, 2023 at 17:33
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    $\begingroup$ Study pion exchange, a decent analog. $\endgroup$ Aug 14, 2023 at 17:35
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    $\begingroup$ maybe my answer here and links therein about the residual strong force will help physics.stackexchange.com/q/35331 $\endgroup$
    – anna v
    Aug 14, 2023 at 17:46

2 Answers 2

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How do atoms interact despite their overall neutrality? They can interact via dipole-dipole interaction. for example. What is the analog here

Despite that every nucleon has white color , the particles which make up the nucleon dont have white color.If you have 2 nucleons very close to each other , some quarks from 1 nucleon will interact with the quarks of the 2nd nucleon

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Neutral objects constructed from charged constituents always feel a contact force when they touch. This is true for any type of charge, and is why we don't fall through the floor even though both us and the floor are (usually) electrically neutral. As @Cerise notes in their answer, once the neutral objects start to overlap, their charged constituents "see" each other and interact.

The details of the interaction depend on the system. As discussed in this answer to "Attraction and repulsion between atoms", neutral atoms are attracted at short distances because their electrons mutually polarize, and then at even shorter distances the atoms repel each other because of Pauli Exclusion. As discussed in this answer to "Can a composite boson like the pion be an exchange particle for the strong nuclear force?", nucleons start to interact when they are close enough to exchange quarks, and the range of such forces is extended because the exchange can be in the form of colour-neutral quark-antiquark meson states such as pions. You might find Peter Dunne's article on "A reappraisal of the mechanism of pion exchange and its implications for the teaching of particle physics" helpful.

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