New answers tagged feynman-diagrams
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Calculating a Feynman diagram with the helicity basis
I found my mistake; the other outgoing particle has an angle $\theta + \pi$ and not also $\theta$. Then the polarization bispinor acquires a phase of $\pi/2$. This answer was based on this post.
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Understanding Feynman Diagrams in Loop Corrections to the propagator $\phi ^3 $ theory
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And to be precise:
$$\tilde{\Delta }(k^2 )=\frac{1}{k^2 +m^2 -i\epsilon }\tag{14.3}$$
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Why is (as Srednicki shows):
$$\int \frac{d^dl}{(2\pi )^d}\tilde{\Delta }((l+k)^2)\tilde{\Delta }(l^2 )$$
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Understanding Feynman Diagrams in Loop Corrections to the propagator $\phi ^3 $ theory
I was asked to expand my comment to an answer. Maybe it would be useful to keep in mind a more physical notion of what the loop diagrams represent.
Recall we are trying to understand our interacting ...
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2PI Effective Action from Double Legendre Transformation
It is difficult to find an explicit reference that really shows this property, but one can convince oneself from eq. (2.17) in PhysRevD.10.2428. Note here that the constant is the log of the free ...
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Feynman rule for scalar QED vertex
It may be easier for you to expand the interaction action term in Fourier space:
$$
\begin{align}
iS_I &= e\int A^\mu(x)(\phi^*(x)\partial_\mu\phi(x)-\phi(x)\partial_\mu\phi^*(x))d^4x \\
&= ie\...
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