The endpoint formalism for the calculation of electromagnetic radiation and its applications in astroparticle physics

TL;DR

The paper introduces the endpoint formalism for calculating electromagnetic radiation, demonstrating its versatility and application in astroparticle physics, especially for complex scenarios beyond classical mechanisms.

Contribution

It presents a universal endpoint formalism that unifies microscopic and macroscopic views of radio emission from air showers, applicable in Monte Carlo simulations.

Findings

Explains the non-Cherenkov nature of Askaryan radiation.

Applied in REAS3 code to unify emission models.

Reproduces classical radiation mechanisms in appropriate limits.

Abstract

We present the "endpoint" formalism for the calculation of electromagnetic radiation and illustrate its applications in astroparticle physics. We use the formalism to explain why the coherent radiation from the Askaryan effect is not in general Cherenkov radiation, as the emission directly results from the time-variation of the net charge in the particle shower. Secondly, we illustrate how the formalism has been applied in the air shower radio emission code REAS3 to unify the microscopic and macroscopic views of radio emission from extensive air showers. Indeed, the formalism is completely universal and particularly well-suited for implementation in Monte Carlo codes in the time- and frequency-domains. It easily reproduces well-known "classical mechanisms" such as synchrotron radiation, Vavilov-Cherenkov radiation and transition radiation in the adequate limits, but has the advantage that it continues to work in realistic, complex situations, where the "classical mechanisms" tend to no longer apply and adhering to them can result in misleading interpretations.