Extended locally monochromatic approximations of Strong-Field QED processes

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Hauptverfasser: Larin, Nikita, Seipt, Daniel
Format: Preprint
Veröffentlicht: 2025
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author Larin, Nikita
Seipt, Daniel
author_facet Larin, Nikita
Seipt, Daniel
contents Strong-field QED (SFQED) probability rates in the locally monochromatic approximation (LMA) have become an indispensable tool for simulations of processes like gamma-ray emission or electron-positron pair production in laser-particle collisions. We revisit the LMA derivation and explicitly demonstrate that it is based on the separation of time scales, neglection of the long-range interference effects and subsequent averaging over the cycle scale. Doing so, we obtain unambiguously LMA rates for arbitrary polarizations of the plane wave background. Additionally, we partially restore the finite bandwidth effects that are lost in the LMA derivation. The bandwidth-restored result we refer to as the LMA$^+$ and show that it agrees with the full SFQED predictions better than the standard LMA. We use LMA$^+$ to address previously inaccessible observables and formulate a new limitation on the applicability of locally monochromatic approximations in general. We provide analytical results for the angular-integrated LMA$^+$ probability rate and the fully differential probability that account for the finite bandwidth effects.
format Preprint
id arxiv_https___arxiv_org_abs_2506_04889
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Extended locally monochromatic approximations of Strong-Field QED processes
Larin, Nikita
Seipt, Daniel
High Energy Physics - Phenomenology
Plasma Physics
Strong-field QED (SFQED) probability rates in the locally monochromatic approximation (LMA) have become an indispensable tool for simulations of processes like gamma-ray emission or electron-positron pair production in laser-particle collisions. We revisit the LMA derivation and explicitly demonstrate that it is based on the separation of time scales, neglection of the long-range interference effects and subsequent averaging over the cycle scale. Doing so, we obtain unambiguously LMA rates for arbitrary polarizations of the plane wave background. Additionally, we partially restore the finite bandwidth effects that are lost in the LMA derivation. The bandwidth-restored result we refer to as the LMA$^+$ and show that it agrees with the full SFQED predictions better than the standard LMA. We use LMA$^+$ to address previously inaccessible observables and formulate a new limitation on the applicability of locally monochromatic approximations in general. We provide analytical results for the angular-integrated LMA$^+$ probability rate and the fully differential probability that account for the finite bandwidth effects.
title Extended locally monochromatic approximations of Strong-Field QED processes
topic High Energy Physics - Phenomenology
Plasma Physics
url https://arxiv.org/abs/2506.04889