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The question is really in the title with this one, I just need a little bit of clarity, consider beta-minus decay, which is an interaction governed by the weak nuclear force, $$n\to p^+ +e^- +\bar v_e$$ Here, the corresponding Feymann Diagram is

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which clearly indicates the $W^-$boson as the exchange particle, acting as proof that the interaction occurs due to the weak nuclear force. The question is, if neutron and protons are subject to the strong nuclear force, how can they be involved in weak interactions?

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  • $\begingroup$ A particle absolutely can be subject to several forces at once. Protons interact with all four fundamental forces, in fact. $\endgroup$
    – Noiralef
    Commented Nov 2, 2017 at 13:09
  • $\begingroup$ It was also called "The Weak Nuclear Force" long before electroweak unification. $\endgroup$
    – JEB
    Commented Nov 2, 2017 at 14:20

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You have to think about the internal structure of protons and neutrons. Neutrons have two down valence quarks and one up valance quark. Protons have two up valance quarks and one down valance quark. At the fundamental level what happens when a neutron decays into a proton is that a down quark from the neutron changes its flavor into an up quark by emitting a $W^{-}$ boson. Quarks do interact through weak interaction.

Here is the Feynman Diagram for beta$^{-}$ decay.

Feynman Diagram - Beta decay

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  • $\begingroup$ You could move the OP's argument one step down: «if [quarks] are subject to the strong nuclear force, how can they be involved in weak interactions?» $\endgroup$
    – user154997
    Commented Nov 2, 2017 at 14:12
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It's not either-or.

Protons and neutrons are subject to the strong force AND the weak force AND the electromagnetic force. And, indeed gravity. The same is true for the quarks that make them up.

Often the strong force effects (cross sections, decays etc) are much larger than weak force effects so one can neglect everything but the strong force. But if an effect is forbidden for the strong force (as beta decay certainly is, because leptons don't feel the strong force) it can give the weak force effects a chance to show themselves.

Gluons and photons are the only (known) particles that don't feel the weak force.

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Well protons and neutrons on top of being subjected to the strong force interact with the weak force. This is because all fermions(left handed fermions) and all anti-fermions(right handed fermions). So one of the quarks can change from one form to another. This results in protons turning into neutrons(also neutrons turning into protons). Well quarks interact with the strong force as that is their force. Also all particles for the most part interact with the weak force(fermions).

http://ecuip.lib.uchicago.edu/multiwavelength-astronomy/astrophysics/06.html

In this article it shows that quarks can interact with strong and weak forces.

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