Quantum Nature of the Big Bang: Improved dynamics

TL;DR

This paper introduces an improved Hamiltonian constraint in loop quantum cosmology, leading to a quantum bounce at Planck-scale densities and resolving previous issues with low-density bounces, thereby enhancing the theory's consistency.

Contribution

The paper presents a new Hamiltonian constraint that ensures the quantum bounce occurs only at Planck-scale densities, improving the physical realism of loop quantum cosmology models.

Findings

Quantum bounce occurs at Planck-scale density.

Quantum evolution remains deterministic across the Planck regime.

The new dynamics resolve the weakness of low-density bounces.

Abstract

An improved Hamiltonian constraint operator is introduced in loop quantum cosmology. Quantum dynamics of the spatially flat, isotropic model with a massless scalar field is then studied in detail using analytical and numerical methods. The scalar field continues to serve as `emergent time', the big bang is again replaced by a quantum bounce, and quantum evolution remains deterministic across the deep Planck regime. However, while with the Hamiltonian constraint used so far in loop quantum cosmology the quantum bounce can occur even at low matter densities, with the new Hamiltonian constraint it occurs only at a Planck-scale density. Thus, the new quantum dynamics retains the attractive features of current evolutions in loop quantum cosmology but, at the same time, cures their main weakness.