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Propagators

With each internal line connecting two vertices one has to be assoicated with a propagator:


\begin{picture}(240,5)
\Text(0,0)[l]{\bf Spin-0}
\put( 60,0){\line(1,0){20}}
\p...
...1,0){8}}
\put(180,0){\line(1,0){20}}
\put(220,0){\line(1,0){20}}
\end{picture}


\begin{displaymath}
\frac{i}{p^2-m^2}
\end{displaymath} (7.377)


\begin{picture}(240,5)
\Text(0,0)[l]{\bf Spin-1/2}
\put( 60,0){\vector(1,0){92}}
\put(152,0){\line(1,0){88}}
\end{picture}


\begin{displaymath}
\frac{i}{\not{\;\!\!\!p}-m} = i\frac{\not{\;\!\!\!p}+m}{p^2-m^2}
\end{displaymath} (7.378)


\begin{picture}(240,40)(0,-20)
\Text(0,0)[l]{\bf Photon}
\put( 60,0){\line(0,1){...
....1}}
\put(82.5,-20){\line(1,0){0.1}}
\Photon(60,0)(240,0){20}{6}
\end{picture}


\begin{displaymath}
\frac{i}{k^2}\left( -g^{\mu\nu} + (1-\zeta) \frac{k^\mu k^\nu}{k^2} \right)
\end{displaymath} (7.379)

for a general $\zeta$ gauge. Calculations are usually performed in Lorentz or Feynman gauge with $\zeta=1$ and photon propagator


\begin{displaymath}
\frac{-ig^{\mu\nu}}{k^2} .
\end{displaymath} (7.380)



Douglas M. Gingrich (gingrich@ ualberta.ca)
2004-03-18