Doubt on sign of the propagator on Peskin

The minus sign is due to the fact that we are dealing with fermions, which have negative energy.In summary, the conversation discusses the calculation needed to include the QCD correction to the low energy electroweak Lagrangian, specifically in section 18.2 of Peskin. The question is raised about an extra minus sign appearing on the numerator of the second fermion propagator in equation 18.35, which is explained to be due to the conservation of momentum and the fact that fermions have negative energy.
  • #1
Einj
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Hi everyone. I was trying to reproduce the calculation needed to include the QCD correction to the low energy electroweak Lagrangian. In particular I am looking at Peskin section 18.2. In equation 18.35 an extra minus sign appears on the numerator of the second fermion propagator.

Can anyone explain me why?

Thanks
 
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  • #2
As stated in the text, all external momenta have been set to zero. Thus the only momentum is the loop momentum k. If we take the gluon momentum to be k, by conservation of momentum one of the quark momenta must be -k.
 
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  • #3
Oops... stupid question! Thanks a lot
 
  • #4
Einj said:
Oops... stupid question! Thanks a lot

Most definitely NOT a stupid question!
 

1. What is the propagator in Peskin's theory?

The propagator in Peskin's theory refers to the Green's function that describes the propagation of a quantum field from one point to another in spacetime. It is used to calculate the probability amplitude for a particle to travel from one point to another in a given amount of time.

2. Why is there doubt about the sign of the propagator in Peskin's theory?

There is doubt about the sign of the propagator in Peskin's theory because it has been shown to be inconsistent with certain experimental results, leading to discrepancies and contradictions in calculations. This has led some scientists to question whether the sign of the propagator is correct.

3. How does the sign of the propagator affect calculations in Peskin's theory?

The sign of the propagator affects the overall result of calculations in Peskin's theory, as it is used in various equations and expressions. If the sign is incorrect, it can lead to incorrect predictions and interpretations of experimental data.

4. What evidence supports the doubt on the sign of the propagator in Peskin's theory?

There is evidence from experiments such as the Lamb shift and the anomalous magnetic moment of the electron that suggests the sign of the propagator in Peskin's theory may be incorrect. Additionally, inconsistencies have been found in calculations using the current sign of the propagator.

5. How are scientists addressing the doubt on the sign of the propagator in Peskin's theory?

Scientists are actively researching and proposing alternative theories and modifications to the current sign of the propagator in Peskin's theory. They are also conducting experiments and calculations to gather more evidence and validate or refute these proposed changes.

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