- #1
Elmo
- 35
- 6
- TL;DR Summary
- Basically this :
Why do we have to take the trace of the numerator when calculating the vacuum polarization loop ?
Sorry I just typed out my query .For some reason I can't seem to find the buttons for attaching files on this thread.
When writing the QED vacuum polarization loop, the numerator ,consisting momenta slashed + m from the fermion propagators and the two gamma matrices, has a trace over all of it.
Yet we do not take traces in other loop diagrams like fermion self energy or vertex correction.
Couldn't figure out why. Some clarification on it will be most helpful.
My best (and very vague) guess is that it has got something to do with the spinor completeness relation.
For reference see page 308 of Schwartz.
When writing the QED vacuum polarization loop, the numerator ,consisting momenta slashed + m from the fermion propagators and the two gamma matrices, has a trace over all of it.
Yet we do not take traces in other loop diagrams like fermion self energy or vertex correction.
Couldn't figure out why. Some clarification on it will be most helpful.
My best (and very vague) guess is that it has got something to do with the spinor completeness relation.
For reference see page 308 of Schwartz.