Low Energy States and CPT invariance at the Big Bang

TL;DR

This paper constructs and analyzes quantum vacuum states in a radiation-dominated, CPT-invariant universe, ensuring ultraviolet regularity and Hadamard conditions, and proposes these as effective quantum vacua at the Big Bang.

Contribution

It extends the States of Low Energy proposal to spin-1/2 fields in FLRW spacetime and demonstrates their suitability as self-consistent quantum vacua at the Big Bang.

Findings

States satisfy Hadamard/adiabatic condition

Vacua minimize smeared energy density

States are consistent candidates for Big Bang quantum vacuum

Abstract

In this paper, we analyze the quantum vacuum in a radiation-dominated and CPT-invariant universe by further imposing the quantum states to be ultraviolet regular i.e., satisfying the Hadamard/adiabatic condition. For scalar fields, this is enforced by constructing the vacuum via the States of Low Energy proposal. For spin-$\frac{1}{2}$ fields, we extend this proposal for a FLRW spacetime and apply it for the radiation-dominated and CPT-invariant universe. We focus on minimizing the smeared energy density around the Big Bang and give strong evidence that the resulting states satisfy the Hadamard/adiabatic condition. These states are then self-consistent candidates as effective Big Bang quantum vacuum from the field theory perspective.