A general-covariant concept of particles in curved background

TL;DR

This paper develops a local particle current concept in curved spacetime for scalar fields, exploring how different two-point function choices affect local conservation and particle production descriptions.

Contribution

It introduces a general-covariant local particle current in curved backgrounds, analyzing its dependence on two-point function choices and their implications for local conservation.

Findings

A specific two-point function choice yields local non-conservation and particle production.

Another natural choice results in a locally conserved particle current.

The local description aligns with global Bogoliubov transformation results.

Abstract

A local current of particle density for scalar fields in curved background is constructed. The current depends on the choice of a two-point function. There is a choice that leads to local non-conservation of the current in a time-dependent gravitational background, which describes local particle production consistent with the usual global description based on the Bogoliubov transformation. Another choice, which might be the most natural one, leads to the local conservation of the current.