Localized Particle States and Dynamics Gravitational Effects

TL;DR

This paper investigates the unique behavior of localized scalar particles in de Sitter space, revealing persistent energy oscillations and spread-out interactions, with implications for detecting ultralow-mass scalar particles in an expanding universe.

Contribution

It constructs explicit localized particle and wave packet states in de Sitter space and analyzes their energies and detector responses, highlighting novel quantum field effects in curved spacetime.

Findings

Localized states exhibit perpetual energy oscillations.

Wave packets show spread-out energy interactions.

Numerical results confirm theoretical predictions.

Abstract

Scalar particles--i.e., scalar-field excitations--in de Sitter space exhibit behavior unlike either classical particles in expanding space or quantum particles in flat spacetime. Their energies oscillate forever, and their interactions are spread out in energy. Here it is shown that these features characterize not only normal-mode excitations spread out over all space, but localized particles or wave packets as well. Both one-particle and coherent states of a massive, minimally coupled scalar field in de Sitter space, associated with classical wave packets, are constructed explicitly. Their energy expectation values and corresponding Unruh-DeWitt detector response functions are calculated. Numerical evaluation of these quantities for a simple set of classical wave packets clearly displays these novel features. Hence, given the observed accelerating expansion of the Universe, it is possible that observation of an ultralow-mass scalar particle could yield direct confirmation of distinct predictions of quantum field theory in curved spacetime.