New geometric and field theoretic aspects of a radiation dominated universe

TL;DR

This paper explores a novel inhomogeneous spacetime derived from a radiation dominated universe, revealing unique geometric, horizon, and quantum field properties, including new particle creation phenomena.

Contribution

It introduces a new conformally transformed spacetime metric with distinctive properties and analyzes its implications for horizon structure and quantum field quantization.

Findings

Static observers see no horizon in the new spacetime

Non-static observers can encounter horizons similar to Rindler horizons

The new metric allows a different quantization of scalar fields and shows particle creation

Abstract

The homogeneous and isotropic radiation dominated universe, following the inflationary stage, is expressed as a spherically symmetric and inhomogeneous spacetime upon a power law type conformal transformation of the null (cosmological) coordinates. This new spacetime metric has many interesting properties. While the static observers, at a fixed position in this new spacetime, do not see any horizon, some non-static observers encounter a horizon due to their motion which is analogous to the situation of Rindler observers in Minkowski spacetime. The symmetry of the new metric offers a unitarily inequivalent quantization of the massless scalar field and provides a new example of particle creation. We calculate the particle content of the cosmological vacuum state with respect to the static observer in this new spacetime who, with respect to cosmological time, is freely falling in asymptotic past and future but accelerated in between.