A "transforming" interaction...
Nature uses the weak interaction as a tool when it needs to transform matter. The weak interaction involves particle in pairs: for example, neutron with proton, down quarks with up, electron with neutrino, positron with antineutrino. In each of these "doublets", the electric charge of the two particles differ by one unit. It is by changing its electrical charge and thus its nature, that the weak interaction converts a member of the doublet into another.
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