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advanced_notions:quantum_field_theory:nfrared_divergences
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Infrared Divergences
Why is it interesting?
Layman
Explanations in this section should contain no formulas, but instead colloquial things like you would hear them during a coffee break or at a cocktail party.
Student
In this section things should be explained by analogy and with pictures and, if necessary, some formulas.
Researcher
Scattering amplitudes in perturbative QED and gravity suffer from infrared divergences. These well understood divergences arise from our inability to distinguish between a “hard” particle with or without “soft hair”. (In non-abelian theories there are also collinear IR divergences. As these are absent in QED (and also in gravity) we will not discuss them here.) Hence, a physical asymptotic state entering any scattering process is a super-position of the hard particle with all possible soft hair arrangements. The way to construct the physical asymptotic states that yield an IR safe S-matrix was put forward by Kulish and Faddeev [10]. In their construction, the dressed incoming and outgoing states diagonalize the interacting asymptotic Hamiltonian. Once the S-matrix of these dressed electrons is expanded in perturbation theory, the cancellation of IR divergences is ensured by the existence of soft theorems.https://arxiv.org/pdf/1607.08599.pdf
Examples
- Example1
- Example2:
FAQ
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advanced_notions/quantum_field_theory/nfrared_divergences.1510577263.txt.gz · Last modified: 2017/12/04 08:01 (external edit)
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