W boson vertices

by kaksmet
Tags: boson, vertices
 P: 91 First of all remember that an interaction vertex in the lagrangian can represent several different processes in feynman diagrams. the $W^{-}u\bar{d}$ term in the lagrangian can be the decay $W^{+}\rightarrow u\bar{d}$ or the annhilation $d\bar{u}\rightarrow W^{-}$ , both with the same coupling (including the same phase) the conjugate decay and annihilation processes will come from the hermitian conjugate term in the lagrangian, and they will have opposite phase. A useful way to remember which processes will have the same phase and which will not is to remember that the CPT inversed process has the same coupling (including the same phase). In our case $W^{+}\rightarrow u\bar{d}$ is the CPT inversed process of $d\bar{u}\rightarrow W^{-}$ , since each particle is replaced by its antiparticle and the time direction is reversed.