Packaging particles in curved spacetimes

TL;DR

This paper examines the limitations of using wave packets for defining the S-matrix in curved spacetimes, highlighting conceptual issues and proposing a more general approach for scattering calculations.

Contribution

It demonstrates that wave packet methods are insufficient in curved spacetimes and introduces a new approach for scattering calculations in such contexts.

Findings

Wave packets do not fully resolve singularities in curved spacetime S-matrix definitions.

Standard textbook methods are inadequate for general curved spacetime scattering.

A proposed method for more accurate scattering calculations in curved spacetimes.

Abstract

Scattering calculations in curved spacetime are technically complicated and, in the case of a general spacetime metric, quite impossible. Even in the cases where perturbative scattering calculations can be done one has to be careful about what kind of particles are sensible to measure. Curved spacetime quantum field theories are then less conceptually clear than those in flat spacetime. In this article, we investigate an aspect of this conceptual confusion - the use of wave packets in defining the S-matrix. Wave packets are used in most standard textbook treatments to construct particle states and remove certain singularities in the definition of the S-matrix. We show that this method does not completely work in curved spacetimes first in a general way and then by way of a specific model. We also discuss related effects and suggest a method for doing curved spacetime scattering calculations. Our conclusion is that the most general method for scattering calculations in curved spacetimes requires the use of wave packets, which are typically absent in the literature.