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Quantum Field Theory

Weak Interaction

Weak Interaction in Picture Of the 4 different kinds of forces in the universe, gravity is attractive; electromagnetic force can be attractive or repulsive; the strong force provides a powerful attraction at short distance; the weak force works in very short distance, its action is to change one form of particle into another such as the beta decay of a free neutron in Figure 03k (strong force in stable nucleus inhibits the neutrons from beta decay). Note that the simple picture in Figure 03k already embraced the conservation of mass-energy, charge, and lepton number (nl).

Figure 03k Weak Interaction in Picture [view large image]

The strength of these forces varies according to the separation between particles, but in term of their coupling constants the ratio between the strong, electric, weak, and gravity is about 1 : 10-2 : 10-13 : 10-38. The understanding of the weak force took many twists and turns.

Its historical development includes the discovery of neutrino, the introduction of Fermi's theory, the violation of parity, the selection of V - A interaction, its adoption to the gauge theory and finally incorporation into the Standard Model (see next section). All these subjects will be presented in some details below.

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