Constraining Quantum Initial Conditions before Inflation

TL;DR

This paper explores various initial quantum states before inflation, comparing their observational signatures and finding no strong preference among them, while also proposing frozen initial conditions as an alternative explanation for CMB observations.

Contribution

It systematically analyzes different pre-inflationary quantum vacuum choices and introduces frozen initial conditions as a viable alternative to quantum vacuum inflation.

Findings

Different vacua produce distinguishable observational signatures.

No significant evidence favors any specific vacuum choice over others.

Frozen initial conditions can replicate inflationary predictions for CMB anisotropies.

Abstract

We theoretically and observationally investigate different choices of initial conditions for the primordial mode function that are imposed during an epoch preceding inflation. By deriving predictions for the observables resulting from several alternate quantum vacuum prescriptions we show some choices of vacua are theoretically observationally distinguishable from others. Comparing these predictions to the Planck 2018 observations via a Bayesian analysis shows no significant evidence to favour any of the quantum vacuum prescriptions over the others. In addition we consider frozen initial conditions, representing a white-noise initial state at the big-bang singularity. Under certain assumptions the cosmological concordance model and frozen initial conditions are found to produce identical predictions for the cosmic microwave background anisotropies. Frozen initial conditions may thus provide an alternative theoretic paradigm to explain observations that were previously understood in terms of the inflation of a quantum vacuum.