Semiclassical predictions regarding a pre-inflationary era and its effects on the power spectrum

TL;DR

This paper explores how a pre-inflationary, radiation-dominated era influences the cosmic microwave background power spectrum, revealing suppression at large angles and oscillations depending on the quantum state of scalar fields.

Contribution

It introduces a simple model combining classical radiation and a cosmological constant to analyze pre-inflationary effects on the CMB power spectrum, considering various quantum states.

Findings

Power spectrum suppressed at large angles.

Oscillations in the power spectrum with state-dependent amplitudes.

Effects depend on the choice of quantum state for scalar fields.

Abstract

An investigation is undertaken into the properties and effects of a preinflationary era during at least part of which semiclassical gravity was valid. It is argued that if the Universe (or our part of it) was approximately homogeneous and isotropic during that era, then the Universe was likely to have been radiation dominated. A simple model in which the Universe contains classical radiation and a cosmological constant is used to investigate potential effects of such a preinflationary era on the cosmic microwave background. The power spectrum is computed using the mode functions of a quantized massless minimally coupled scalar field. Various choices of state for this field are considered, including adiabatic vacuum states of various orders and the vacuum state that would naturally occur if the Universe made a sudden transition from being radiation dominated to de Sitter space. In all cases investigated, there is a suppression of the power spectrum at large angles, and, when plotted as a function of the momentum parameter, there are always oscillations with state-dependent amplitudes.