Semiclassical Mixmaster Universe

TL;DR

This paper investigates the semiclassical behavior of the Mixmaster universe with a scalar field, revealing multiple bounces, anisotropy fluctuations, and reduced chaos due to spacetime discreteness effects.

Contribution

It introduces a semiclassical framework for Mixmaster cosmology with scalar fields, analyzing effects of spacetime discreteness and quantum corrections on dynamics.

Findings

Effective cosmology exhibits multiple small bounces before expansion.

Anisotropies fluctuate significantly during bounces, especially with matter.

Chaos is reduced in effective models compared to classical Mixmaster universe.

Abstract

We present a semiclassical study of the Mixmaster cosmology minimally coupled to a massive scalar field in the Hamiltonian formalism, with focus on three distinct scenarios: the classical cosmology coupled to the quantized scalar field, and "effective" cosmology, with spacetime discreteness corrections, coupled to the classical scalar field, and to the quantized scalar field. We find several results: (i) the effective cosmology undergoes several small bounces before expanding, with scalar field excitations rising through the bounce; (ii) anisotropies rise and fall as the universe undergoes a bounce, a feature that is enhanced with matter; (iii) Lyapunov exponents reveal that chaos is reduced in the effective systems compared to the classical case.