Particle creation in the effective action method

TL;DR

This paper develops a systematic method using the nonlocal effective action to calculate particle creation by external fields, linking quantum particle production to classical radiation phenomena.

Contribution

It provides a novel, systematic derivation of particle creation effects from the effective action framework applicable to arbitrary external fields.

Findings

Derived a simple functional form for particle creation energy in external fields.

Linked quantum particle production to classical radiation via the radiation moment.

Analyzed vacuum radiation of an electrically charged source.

Abstract

The effect of particle creation by nonstationary external fields is considered as a radiation effect in the expectation-value spacetime. The energy of created massless particles is calculated as the vacuum contribution in the energy-momentum tensor of the expectation value of the metric. The calculation is carried out for an arbitrary quantum field coupled to all external fields entering the general second-order equation. The result is obtained as a functional of the external fields. The paper gives a systematic derivation of this result on the basis of the nonlocal effective action. Although the derivation is quite involved and touches on many aspects of the theory, the result itself is remarkably simple. It brings the quantum problem of particle creation to the level of complexity of the classical radiation problem. For external fields like the electromagnetic or gravitational field there appears a quantity, the radiation moment, that governs both the classical radiation of waves and the quantum particle production. The vacuum radiation of an electrically charged source is considered as an example. The research is aimed at the problem of backreaction of the vacuum radiation.