Loop Quantum Gravity on Dynamical Lattice and Improved Cosmological Effective Dynamics with Inflaton

TL;DR

This paper develops a new dynamical lattice approach in Loop Quantum Gravity to derive improved cosmological effective dynamics, resolving singularities and incorporating inflation, with results similar to established LQC models.

Contribution

It introduces a dynamic lattice framework in LQG for cosmology, enhancing previous models by resolving singularities and integrating inflationary dynamics.

Findings

Recovers FLRW cosmology at low energy density

Resolves big-bang singularity with a bounce

Emerges de-Sitter spacetime and cosmological constant from quantum effects

Abstract

In the path integral formulation of the reduced phase space Loop Quantum Gravity (LQG), we propose a new approach to allow the spatial cubic lattice (graph) to change dynamically in the physical time evolution. The equations of motion of the path integral derive the effective dynamics of cosmology from the full LQG, when we focus on solutions with homogeneous and isotropic symmetry. The resulting cosmological effective dynamics with the dynamical lattice improves the effective dynamics obtained earlier from the path integral with fixed spatial lattice: The improved effective dynamics recovers the FLRW cosmology at low energy density and resolves the big-bang singularity with a bounce. The critical density $\rho_c$ at the bounce is Planckian $\rho_c\sim \Delta^{-1}$ where $\Delta$ is a Planckian area serving as certain UV cut-off of the effective theory. The effective dynamics gives the unsymmetric bounce and has the de-Sitter (dS) spacetime in the past of the bounce. The cosmological constant $\Lambda_{eff}$ of the dS spacetime is emergent from the quantum effect $\Lambda_{eff}\sim\Delta^{-1}$. These results are qualitatively similar to the properties of $\bar{\mu}$-scheme Loop Quantum Cosmology (LQC). Moreover, we generalize the earlier path integral formulation of the full LQG by taking into account the coupling with an additional real scalar field, which drives the slow-roll inflation of the effective cosmological dynamics. In addition, we discuss the cosmological perturbation theory on the dynamical lattice, and the relation to the Mukhanov-Sasaki equation.