# What is the mechanism of the Askaryan effect?

(Quoted largely from Wikipedia): Askaryan radiation, known otherwise as the Askaryan effect, is a phenomenon which occurs when a particle traveling faster than the phase velocity of light in a dense dielectric produces a shower of secondary charged particles which contain a charge anisotropy, and thus emits a cone of coherent radiation in the radio part of the electromagnetic spectrum.

As I understand it, on a very high level, the Askaryan effect is similar in nature to the Cherenkov effect (whereby charged particles moving with velocity $$>> c$$ in the vacuum emit radiation), producing radiation by "twanging" atoms, pushing electrons into higher energy states which, of course, subsequently return, "emitting" photons (I could well be wrong, however).

Unfortunately, much (all?) of the information out there on this is buried deep within research papers, and is rather inaccessible.

My question is, what is the mechanism of the Askaryan effect? How does a particle go from traveling through "space", to encountering some matter, to producing coherent radiation, on a low level? What, specifically is meant by charge anisotropy here (I could define it, however I'm not sure what it looks like here), and how is it relevant? That is, I'm looking for a more detailed understanding of what exactly is going on here, including the math where important.

This video has the definition also the history and the use of the effect mainly in neutrino experiments aiming at very high energy neutrinos.

Very high energy cosmic rays hitting the atmosphere create air showers

An air shower is an extensive (many kilometres wide) cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray (i.e. one of extraterrestrial origin) enters the atmosphere.

The detectors have to be spread in large areas to catch the shower of produced particles and get the energy of the incoming cosmic .

It was proposed by Askaryan in the 1960s that very high energy cosmic rays hitting a dense dielectric would produce a shower with the dielectric and the charged particles of the shower would produce coherent low energy electromagnetic radiation, characteristic of the shower.

The effect has been seen in laboratory , and it is important for primary cosmic neutrino experiments. High energy cosmic neutrinos can reach the surface of the earth without interacting, and then, when hitting the ice, for example, the shower of secondary particles creates a coherent radio frequency wavefront due to the interaction with the lattice and atoms of the dielectric.

There are a number of articles , example, proposing calculations for the neutrino experiments. This talk explains the use of the radiation in experiments. In effect the radio frequency comes from the coherent cerenkov effect of the secondary charged particles.

The idea of Askaryan relies on the excess of negative charges in the shower, since positrons tend to disappear through their annihilation into photons, and further electrons are created via Compton scattering by photons. If the number of electrons and positrons is the same, emission would not occur because the electric field generated by opposite charges is equal (in module) and opposite (in sign)

etc.

thanks for drawing my attention to this effect and its use.