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Quantum Damping of Cosmological Shear: A New Prediction from Loop Quantum Cosmologies

Wen-Cong Gan, Leila L. Graef, Rudnei O. Ramos, Gustavo S. Vicente, Anzhong Wang

Abstract

We analyze the dynamics of the Bianchi I universe in modified loop quantum cosmology (Model I, or mLQC-I), uncovering a robust mechanism for isotropization. As in the standard LQC, the classical singularities are resolved by quantum bounce. Remarkably, mLQC-I exhibits a distinctive feature: following the bounce, the shear is dynamically suppressed and decays rapidly to zero within the deep quantum regime. This occurs independently of the collapsing matter fields, leading to a natural quantum isotropization. Consequently, the three spatial directions expand rapidly to macroscopic scales, producing a homogeneous and isotropic universe directly from the quantum epoch without fine-tuning. Our findings demonstrate that mLQC-I not only resolves singularities but also provides a more effective pathway for suppressing anisotropies than other models, thereby reinforcing its viability as a description of the early universe.

Quantum Damping of Cosmological Shear: A New Prediction from Loop Quantum Cosmologies

Abstract

We analyze the dynamics of the Bianchi I universe in modified loop quantum cosmology (Model I, or mLQC-I), uncovering a robust mechanism for isotropization. As in the standard LQC, the classical singularities are resolved by quantum bounce. Remarkably, mLQC-I exhibits a distinctive feature: following the bounce, the shear is dynamically suppressed and decays rapidly to zero within the deep quantum regime. This occurs independently of the collapsing matter fields, leading to a natural quantum isotropization. Consequently, the three spatial directions expand rapidly to macroscopic scales, producing a homogeneous and isotropic universe directly from the quantum epoch without fine-tuning. Our findings demonstrate that mLQC-I not only resolves singularities but also provides a more effective pathway for suppressing anisotropies than other models, thereby reinforcing its viability as a description of the early universe.
Paper Structure (5 sections, 14 equations, 2 figures)

This paper contains 5 sections, 14 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Bianchi I Universe in mLQC-I
  3. Shear in loop quantum cosmologies
  4. Numerical Results
  5. Conclusions

Figures (2)

  • Figure 1: Results for $a_i(t)$ and $a(t)$ for the cases of GR (panel a), LQC (panel b) and mLQC-I (panel c) for the Bianchi I universe filled with dust. The evolution for the shear scalar $\sigma^2(t)$ for each of these cases is shown in panel d. Initial conditions are imposed at $t = 0$.
  • Figure 2: The shear $\sigma^2(t)$ as a function of time in mLQC-I for the cases of a radiation fluid, a massless scalar field, a scalar field with an ekpyrotic potential, and a scalar field with a polynomial chaotic potential. Note that the massless case is almost indistinguishable from the polynomial chaotic case. All results are obtained with the same initial conditions given in the content at the moment $t =0$.