Cosmological perturbations with inverse-volume corrections in loop quantum cosmology

TL;DR

This paper resolves ambiguities in cosmological perturbation equations with inverse-volume corrections in loop quantum cosmology by extending the anomaly-free algebra to spatially closed backgrounds, leading to unique counterterms and quantum-corrected spectra.

Contribution

It introduces a method to fix counterterm ambiguities by using a spatially closed background, enabling consistent derivation of perturbation equations with inverse-volume corrections.

Findings

Unique fixing of counterterms in closed background

Derivation of gauge-invariant perturbation equations

Quantum-corrected scalar and tensor spectra

Abstract

Although the cosmological perturbations with inverse-volume corrections from loop quantum cosmology have been studied using the anomaly-free algebra approach in much of the literature, there still remains an important issue that some counterterms in the perturbed constraints cannot be uniquely fixed on the spatially flat Friedmann-Robterson-Walker background, which causes ambiguities in the perturbation equations. In this paper, we show that this problem can be overcome by extending the anomaly-free algebra to the spatially closed Friedmann-Robterson-Walker background. We find that a consistent deformed algebra can be obtained in the spatially closed case, and each counter term can be uniquely fixed in terms of the inverse-volume correction functions; then, by taking the large $r_o$ limit, we recover the anomaly-free Hamiltonian on the spatially flat background. Using this Hamiltonian we obtain the gauge invariant cosmological perturbations for scalar, vector and tensor modes in the spatially flat case. Moreover, we also derive the quantum-corrected Mukhanov equations, from which the scalar and tensor spectral indices with inverse-volume corrections are given. Some key cosmological perturbation equations obtained in this paper are different from those in previous literature.