New answers tagged s-matrix-theory
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$S$-matrix element in QED (1st Order)
The interaction $\mathcal{L}_{I}$ has just one power of the electromagnetic field. So your Fourier expansion of $A^{\mu}$ only contains terms with a single photon creation or annihilation operator. ...
Buzz♦
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Pole at Infinity of a 1-loop scalar bubble diagram
You have to think about it as having to deform your integration contour to avoid the roots $\alpha_\pm$. When you move along the real $s$ axis, the roots move as follows (the arrows indicate ...
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How are $t$ and $u$ channel processses different?
Well, you are right in that the two diagrams you show for the Compton scattering are indeed equivalent. However, these are neither t- nor u-channel diagrams; the diagrams you show are s-channel ...
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How are $t$ and $u$ channel processses different?
The dependence of the processes on the moemnta are entirely different, being roughly
$$
\frac{1}{(p_2-p_4)^2 -m^2}
$$
for the first and
$$
\frac{1}{(p_2-p_3)^2 -m^2}
$$
for the second.
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