Cosmological Particle Production without Quantum Fields

TL;DR

This paper explores particle production in cosmology from a first quantized perspective, providing new methods to compute occupation numbers and the wavefunction of produced particles, extending understanding beyond quantum field theory.

Contribution

It introduces a first quantized approach to particle production in cosmology, including techniques to calculate occupation numbers and the two-particle wavefunction.

Findings

Derived occupation numbers from vacuum persistence amplitude and Green's function.

Established a method to obtain the two-particle wavefunction of produced quanta.

Extended particle production analysis to extended objects like strings and membranes.

Abstract

In a cosmological setting, particle production is ubiquitous. It may occur as a consequence of the expansion of the background or because a field couples to other degrees of freedom that evolve with time. The process is well understood in the context of quantum field theory, and calculable as long as the produced quanta are weakly interacting. For extended objects like strings and membranes a second quantized formulation is much less developed than for particles. In this light, we revisit particle production from a first quantized perspective. We show how to obtain occupation numbers, both from the vacuum persistence amplitude and from the Green's function. We also derive the much less studied but phenomenologically interesting two-particle wavefunction of the produced quanta.