Renormalization and a non-adiabatic vacuum choice in a radiation-dominated universe

TL;DR

This paper explores a special non-adiabatic vacuum state in a radiation-dominated universe, demonstrating its consistency with renormalization despite unconventional ultraviolet behavior caused by early-time conformal symmetry.

Contribution

It introduces a novel non-adiabatic vacuum state based on early-time conformal symmetry and analyzes its renormalization properties in a radiation-dominated universe.

Findings

The non-adiabatic vacuum state is consistent with renormalization.

Ultraviolet behavior includes oscillatory terms unlike conventional states.

The approach connects early-time conformal symmetry with vacuum choice.

Abstract

Vacuum and particles can be naturally defined in the adiabatic regime of an expanding universe. In general, however, there is no preferred choice of a vacuum state, unless the spacetime background possesses special symmetries. In the absence of symmetries the standard viewpoint is to construct distinguished adiabatic states permitting renormalizability of the stress-energy tensor. We study a special non-adiabatic vacuum for a massive scalar field in a radiation-dominated universe defined by imposing early-times conformal symmetry. We show that this state is consistent with renormalization, despite its ultraviolet behaviour is not the conventional one due to the emergence of oscillatory terms.