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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Qmechanic
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Solidification
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5Search term: residual strong force. – rob Aug 14 '23 at 16:44
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5How do atoms interact despite their overall neutrality? – Jon Custer Aug 14 '23 at 16:48
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@JonCuster They can interact via dipole-dipole interaction. for example. What is the analog here? – Solidification Aug 14 '23 at 17:33
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1Study pion exchange, a decent analog. – Cosmas Zachos Aug 14 '23 at 17:35
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2maybe my answer here and links therein about the residual strong force will help https://physics.stackexchange.com/q/35331/ – anna v Aug 14 '23 at 17:46
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Also see my answer here: https://physics.stackexchange.com/q/288357/ – Lewis Miller Aug 15 '23 at 02:07
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I think this question deserves the opportunity for its own answer unless a closer duplicate can be found. The relevant paragraph in the current "duplicate" hardly seems sufficient: "Nucleons can also interact. In the low energy effective field theory description of nucleons, the relevant degrees of freedom are nucleons and pions, which are color-neutral objects. Nucleons attract each other by exchanging pions." In any event, the OP might want to look at "A reappraisal of the mechanism of pion exchange and its implications for the teaching of particle physics". – David Bailey Aug 15 '23 at 18:26
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Can one actually explain pions and other mesons in terms of "residual force"? It's like asking for the relationship between confinement and chiral symmetry breaking... – Mitchell Porter Aug 17 '23 at 07:54
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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
Cerise
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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.
David Bailey
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