Effective equations of motion and initial conditions for inflation in quantum cosmology

TL;DR

This paper derives effective equations for inflationary dynamics in quantum cosmology, incorporating initial conditions from quantum states, and analyzes their implications for the duration of inflation.

Contribution

It introduces a method to obtain effective inflation equations from quantum states and applies it to models with strong nonminimal coupling, predicting different inflation durations.

Findings

Tunneling state predicts finite inflation duration.

No-boundary state leads to infinite inflation.

Results align with observational constraints on inflation.

Abstract

We obtain effective equations of inflationary dynamics for the mean inflaton and metric fields in the no-boundary and tunneling quantum states of the Universe. In the slow roll approximation (taking the form of the local Schwiger-DeWitt expansion) effective equations follow from the Euclidean effective action on the DeSitter gravitational instanton. Effective equations are applied in the model of the inflaton scalar field coupled to the GUT sector of matter fields and also having a strong nonminimal coupling to the curvature. The inverse of its big negative nonminimal coupling constant, serves as a small parameter of the slow roll expansion and semiclassical expansion of quantum gravitational effects. As a source of initial conditions we use a sharp probability peak recently obtained in the one-loop approximation for the no-boundary and tunneling quantum states and belonging (in virtue of a strong nonminimal coupling) to the GUT energy scale much below the Planck scale. The obtained equations in the tunneling quantum state predict a finite duration of inflationary stage compatible with the observational status of inflation theory, whereas for the no-boundary state they lead to the infinite inflationary epoch with a constant inflaton field.