# On the coherent emission of radio frequency radiation from high energy particle showers

## TL;DR

This paper analyzes the conditions under which radio frequency emission from high-energy cosmic ray showers is coherent, providing a detailed analytical formulation that unifies coherent and incoherent mechanisms, with applications to Cherenkov and geosynchrotron radiation.

## Contribution

It offers a comprehensive analytical framework for understanding coherence conditions in radio emissions from cosmic ray showers, extending prior simplified assumptions.

## Key findings

- Derived a unified formula for coherent and incoherent emissions.
- Confirmed the coherence conditions for Cherenkov radiation.
- Validated the approach with applications to geosynchrotron radiation.

## Abstract

Extended Air Showers produced by cosmic rays impinging on the earth atmosphere irradiate radio frequency radiation through different mechanisms. Upon certain conditions, the emission has a coherent nature, with the consequence that the emitted power is not proportional to the energy of the primary cosmic rays, but to the energy squared. The effect was predicted in 1962 by Askaryan and it is nowadays experimentally well established and exploited for the detection of ultra high energy cosmic rays. In this paper we discuss in details the conditions for coherence, which in literature have been too often taken for granted, and calculate them analytically, finding a formulation which comprehends both the coherent and the incoherent emissions. We apply the result to the Cherenkov effect, obtaining the same conclusions derived by Askaryan, and to the geosynchrotron radiation.