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All are dimensionless constants. With $\frac{e^2}{\hbar c} \approx \frac{1}{137.036}$ Similarly there are constants for weak and colour charge. These basically are the probability over time of a particle emitting a photon, W (or Z)-boson or gluon respectively. The weak constant is of the same order as the electromagnetic constant. The colour constant ...

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I think that you are looking for the helicity suppression, this is simpler to understand for the decay of a $\pi$. In leptonic decays you can separate the hadronic part and the leptonic one. You will get for the matrix element something like that: \$ M \propto f_{\pi}p_{\mu}^{\pi}\bar{u}_{\nu_l}\gamma^{\mu}(1-\gamma_5)v_l \\ ...

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Low energy neutrino and antineutrino can annihilate into three photons, but with an extremely low cross-section. So it's not "never", it's "hardly ever" (http://www.sciencedirect.com/science/article/pii/0029558266902331)

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I would say the approach here is based on scale. I have no references on this, I am exposing my educated guess. I think there is a relation between the energy transfer and the relevant scale receiving this energy. That is how I would explain the difference between pushing a wood piece, with a rather slow movement, while a skilled martial artist is able to ...

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This question is experimentally accessible, despite the feebleness of the weak interaction, because the strong and electromagnetic interactions are symmetric under parity transformations and the weak interaction is not. The contribution to the binding energy is small enough that it's not a good way to think of things. Better is to continue the process of ...

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From this blog post of mine, one should be inclined to think that for large nuclei it can at least contribute to the spin-orbit force, and then to the correction to N=50 and N=82 nuclear shells. As QGR noted above, the exponential suppression of the potential does not need to be all the history. Note that usually the total potential in a nucleus is ...

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