Observational consequences of Bianchi I spacetimes in loop quantum cosmology

TL;DR

This paper investigates how anisotropic Bianchi I models in loop quantum cosmology influence cosmic perturbations and the CMB, revealing observable anisotropic signatures and quantum entanglement effects that align with some Planck satellite observations.

Contribution

It extends perturbation analysis in loop quantum cosmology to anisotropic Bianchi I models, predicting distinctive CMB features and entanglement effects.

Findings

Anisotropic bounce causes quadrupolar modulation in CMB.

Quantum entanglement between scalar and tensor modes affects polarization.

Predictions are consistent with current observational constraints.

Abstract

Anisotropies generically dominate the earliest stages of expansion of a homogeneous universe. They are particularly relevant in bouncing models, since shears grow in the contracting phase of the cosmos, making the isotropic situation unstable. This paper extends the study of cosmological perturbations in loop quantum cosmology (LQC) to anisotropic Bianchi I models that contain a bounce followed by a phase of slow-roll inflation. We show that, although the shear tensor dilutes and the universe isotropizes soon after the bounce, cosmic perturbations retain memory of this short anisotropic phase. We develop the formalism needed to describe perturbations in anisotropic, effective LQC, and apply it to make predictions for the cosmic microwave background (CMB), while respecting current observational constraints. We show that the anisotropic bounce induces: (i) anisotropic features in all angular correlation functions in the CMB, and in particular a quadrupolar modulation that can account for a similar feature observed in the temperature map by the Planck satellite, and (ii) quantum entanglement between scalar and tensor modes, that manifests itself in temperature-polarization (T-B and E-B) correlations in the CMB.