Primordial perturbations in kinetically dominated regimes of general relativity and hybrid quantum cosmology

TL;DR

This paper investigates how scalar field potentials influence primordial perturbations during kinetically dominated early universe phases, affecting their effective mass and vacuum state, with implications for observable cosmological anisotropies.

Contribution

It provides a detailed analysis of the effects of scalar potentials on primordial perturbations in kinetically dominated regimes within general relativity and quantum cosmology, highlighting modifications to effective mass and vacuum selection.

Findings

Scalar potentials modify the effective mass of perturbations.

Vacuum state choices depend on the potential and background dynamics.

Potential effects influence observable cosmological anisotropies.

Abstract

Scalar fields with an energy density dominated by its kinetic part may have played a relevant role in the very early stages of the Universe. Compared to the standard inflationary paradigm, they may lead to modifications in observable quantities, e.g. the anisotropies found in the cosmic microwave background. Kinetically dominated regimes arise in classical fast-roll scenarios as well as in quantum bouncing cosmologies. For instance, kinetic dominance is typical in interesting preinflationary phases of Loop Quantum Cosmology. In this work, we analyze the leading-order effects that the presence of a scalar field potential causes on the primordial cosmological perturbations in these kinetically dominated epochs. These effects can be grouped in two sets, namely, those that affect the effective mass of the perturbations and those that affect the choice of their vacuum state. The effective mass is modified directly by terms that include the potential, but also indirectly by the change in the background dynamics and the relation between the parameterization of these dynamics and the conformal time, usually employed to describe the evolution of the perturbations. On the other hand, away from de Sitter inflation, the Bunch-Davies state is no longer the most natural vacuum at all scales. Recent proposals suggest to modify it by carrying out certain Hamiltonian diagonalization with a suitable asymptotic behavior at large wavenumber scales. Both this diagonalization condition and the imposed asymptotic behavior depend on the effective mass of the perturbations, and therefore the selected vacuum state varies in the presence of the scalar field potential.