The Vacuum State of Primordial Fluctuations in Hybrid Loop Quantum Cosmology

TL;DR

This paper examines how the choice of vacuum state influences the primordial power spectra in hybrid Loop Quantum Cosmology, highlighting differences between adiabatic and non-oscillating vacua during the preinflationary bounce.

Contribution

It provides a detailed analysis of vacuum choices in hybrid Loop Quantum Cosmology and their impact on primordial fluctuations, including the effects of initial conditions at the bounce.

Findings

Adiabatic vacua cause suppressed large-scale power and rapid oscillations.

Non-oscillating vacuum results in large-scale power suppression without oscillations.

Oscillations are linked to initial adiabatic conditions in kinetic dominance.

Abstract

We investigate the role played by the vacuum of the primordial fluctuations in hybrid Loop Quantum Cosmology. We consider scenarios where the inflaton potential is a mass term and the unperturbed quantum geometry is governed by the effective dynamics of Loop Quantum Cosmology. In this situation, the phenomenologically interesting solutions have a preinflationary regime where the kinetic energy of the inflaton dominates over the potential. For these kind of solutions, we show that the primordial power spectra depend strongly on the choice of vacuum. We study in detail the case of adiabatic states of low order and the non-oscillating vacuum introduced by Mart\'in de Blas and Olmedo, all imposed at the bounce. The adiabatic spectra are typically suppressed at large scales, and display rapid oscillations with an increase of power at intermediate scales. In the non-oscillating vacuum, there is power suppression for large scales, but the rapid oscillations are absent. We argue that the oscillations are due to the imposition of initial adiabatic conditions in the region of kinetic dominance, and that they would also be present in General Relativity. Finally, we discuss the sensitivity of our results to changes of the initial time and other data of the model.