What is a loop (in Feynman Diagrams)?

In summary, a loop in physics refers to a self-interaction of particles, represented by a loop in a Feynman diagram. In this particular case, the loop can be modeled as a self-interaction by mass with a factor of -im^2. The loop can take on any momentum through virtual particles, and when there are additional external lines on the loop, it represents new physical processes. This loop may also be referred to as vacuum polarization.
  • #1
Sekonda
207
0
Hey,

I was wondering what exactly a loop is of this kind :

Loop.png


I understand the initial & final four momentums to be the same and so there is no boundary on the possible allowed momentums in the loop.

My professor said the loop is equal to (or can be modeled as) the self-interaction by mass with factor -im^2.

My question is what does this loop represent? I think it is just a self-interaction which can take any momentum by means of 'off-shell' or virtual particles, does this mean all self-interactions regardless of their momenta are virtual particles when represented by a loop or only ones constrained to some set of momenta's?

Thanks,
SK
 
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  • #2
That particular loop doesn't make much sense, since it gets absorbed in the definition of a proton. Where it matters is when you have additional external lines on the loop. These represent new physical processes.
 
  • #3

Related to What is a loop (in Feynman Diagrams)?

What is a loop in Feynman Diagrams?

A loop in Feynman Diagrams refers to a closed line that connects two vertices in a particle interaction. It represents the exchange of a virtual particle between two particles involved in the interaction.

What is the purpose of including loops in Feynman Diagrams?

Including loops in Feynman Diagrams allows for a more accurate representation of particle interactions. It takes into account the effects of virtual particles, which cannot be observed directly but have a significant impact on the behavior of particles.

How do loops affect the calculation of amplitudes in Feynman Diagrams?

Loops can complicate the calculation of amplitudes in Feynman Diagrams as they introduce additional mathematical terms. However, they are necessary for a more precise calculation and can lead to a better understanding of the underlying physics.

Can loops be observed in experiments?

No, loops cannot be directly observed in experiments. They are a mathematical tool used to describe the behavior of particles and their interactions. However, their effects can be observed indirectly through the behavior of particles in experiments.

Are loops present in all Feynman Diagrams?

Not all Feynman Diagrams contain loops. They are only present in diagrams that involve interactions between particles with mass. For example, electromagnetic interactions do not involve loops as photons, the virtual particles exchanged, have zero mass.

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