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An accelerated electron emits photons (which once was the problem for the old atomic model because it implies the electron should spiral down on the nucleus, which it to a certain extent does in discrete steps, but it halts in the lowest available orbital). It's discussed in this question.

Bremsstrahlung (German for "deceleration radiation") occurs when a charge is decelerated. For example, a charge entering an electric field, or interacting with another electron. Which is understandable as the field around the electron undergoes a sudden change.

If we express this by means of a Feynman diagram with the time axis vertically and the space axis horizontally (a procedure which can be doubted, but defended just as well), the associated Feynman diagram is simple:

enter image description here

Do we simply add a curly external leg to an outgoing leg, corresponding to a real photon? Like we can add bubbles to them, like for the anomalous magnetic moment:

enter image description here

The right side of the diagram stays the same.

Can we, for Bremsstrahlung, just add a real external photon curly?

DanielC
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MatterGauge
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  • note that the process $e^-e^- \to \gamma$ (as depicted in your second diagram) cannot be put on-shell, so it cannot describe a physical process, but rather a vertex correction –  Jun 08 '22 at 08:36
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    Yes, just add real photons to the external legs. Actually, all these processes involving electrons already radiated soft and collinear photons, most of them virtual. So much so that this leads to the famous infrared divergences of QED, which are canceled by internal loops. Bremsstrahlung is simply some of these photons going on-shell due to a hard momentum transfer to the charged particle.. – Vinicius Névoa Jun 08 '22 at 08:36
  • see these lowest order diagrams for brems https://physics.stackexchange.com/questions/187934/quantum-mechanics-prediction-for-bremsstrahlung/187935#187935 also this https://www.sarthaks.com/454203/draw-feynman-diagrams-for-a-bremsstrahlung-b-pair-production – anna v Jun 08 '22 at 11:08
  • @annav It's all clear in the meantime. But thanks anyway! – MatterGauge Jun 08 '22 at 11:15
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    @yyy That's why I write it's connected to the right part of the upper diagram, which stays the same. – MatterGauge Jun 08 '22 at 11:16

1 Answers1

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Actually, the Feynman diagram for Bremsstrahlung is that of Compton scattering with the little difference that the incoming photon at the "first" vertex is a virtual one that is generated by a nucleus the electron is scattered at. The electrons "feels" its electromagnetic field symbolized by a virtual photon in the Compton scattering Feynman diagram and emits a real photon (the Bremsstrahlung photon -- the outgoing photon) at the "second" vertex, while the electron exits. Of course corresponding higher order diagrams with loops could be also taken into account, however, their effect is according to perturbation theory minor.

Frederic Thomas
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