Unitarily inequivalent quantum cosmological bouncing models

TL;DR

This paper investigates the ambiguity in variable choice during quantization of bouncing cosmological models, revealing potential predictability issues that are less prominent in inflationary scenarios due to their monotonic scale factor behavior.

Contribution

It demonstrates that unitarily inequivalent quantizations in bouncing models can lead to incompatible predictions, highlighting a fundamental ambiguity absent in inflationary models.

Findings

Ambiguity in variable choice affects quantum predictions in bouncing models.

Inflationary models avoid this ambiguity due to monotonic scale factor.

Bouncing scenarios may face predictability issues because of this ambiguity.

Abstract

By quantising the background as well as the perturbations in a simple one fluid model, we show that there exists an ambiguity in the choice of relevant variables, potentially leading to incompatible observational physical predictions. In a classical or quantum inflationary background, the exact same canonical transformations lead to unique predictions, so the ambiguity we put forward demands a semiclassical background with a sufficiently strong departure from classical evolution. The latter condition happens to be satisfied in bouncing scenarios, which may thus be having predictability issues. Inflationary models could evade such a problem because of the monotonic behavior of their scale factor; they do, however, initiate from a singular state which bouncing scenarios aim at solving.