Cosmological particle creation: Fluctuations and an ensemble picture

TL;DR

This paper investigates quantum particle creation in cosmology, highlighting fluctuations around mean values and proposing an ensemble interpretation using localized wave packets, with implications for understanding reheating after inflation.

Contribution

It introduces an ensemble framework for cosmological particle creation using localized wave packets, addressing nonlocality and fluctuations in particle number.

Findings

Particle number fluctuations are significant and deviate from the mean.

An ensemble interpretation clarifies the meaning of particle number in quantum fields.

Reexamines reheating after inflation with the new ensemble perspective.

Abstract

We point out that in the context of quantum fields in time dependent classical backgrounds, the number of created particles with a given momentum largely deviates about its mean value. Since the corresponding Fourier modes are nonlocal, this deviation shows that the expectation value of the number operator can only make sense in an ensemble of spacetimes. Using a complete orthonormal family of localized wave packets, we show how an ensemble interpretation can be given to cosmological particle creation in local terms. The reheating process following inflation is reexamined in the light of this construction.