# Time evolution in deparametrized models of loop quantum gravity

## TL;DR

This paper introduces a perturbative approximation method for analyzing quantum evolution in deparametrized loop quantum gravity models, enabling more precise computation of physical states and observables over time.

## Contribution

It develops a perturbative approach based on quantum mechanics to approximate the spectral decomposition of Hamiltonians in deparametrized LQG models, facilitating evolution analysis.

## Key findings

- Successfully applied the method to models with scalar and dust fields as time variables.
- Demonstrated the computation of volume and curvature expectation values over time.
- Provided a first step towards controlling the dynamics in deparametrized LQG.

## Abstract

An important aspect in understanding the dynamics in the context of deparametrized models of LQG is to obtain a sufficient control on the quantum evolution generated by a given Hamiltonian operator. More specifically, we need to be able to compute the evolution of relevant physical states and observables with a relatively good precision. In this article, we introduce an approximation method to deal with the physical Hamiltonian operators in deparametrized LQG models, and apply it to models in which a free Klein-Gordon scalar field or a non-rotational dust field is taken as the physical time variable. This method is based on using standard time-independent perturbation theory of quantum mechanics to define a perturbative expansion of the Hamiltonian operator, the small perturbation parameter being determined by the Barbero-Immirzi parameter $\beta$. This method allows us to define an approximate spectral decomposition of the Hamiltonian operators and hence to compute the evolution over a certain time interval. As a specific example, we analyze the evolution of expectation values of the volume and curvature operators starting with certain physical initial states, using both the perturbative method and a straightforward expansion of the expectation value in powers of the time variable. This work represents a first step towards achieving the goal of understanding and controlling the new dynamics developed in [25, 26].