A relational Hamiltonian for group field theory

TL;DR

This paper develops a relational Hamiltonian framework for group field theory using a scalar field as a clock, leading to quantum cosmological models that reproduce Friedmann dynamics and predict a bounce replacing the big bang singularity.

Contribution

It introduces a relational Hamiltonian for group field theory and demonstrates its application to condensate states, connecting quantum gravity with classical cosmology.

Findings

Exact agreement with Friedmann equations in the classical limit

Quantum corrections replace the big-bang with a bounce

Framework enables a relational quantum dynamics approach

Abstract

Using a massless scalar field as a clock variable, the Legendre transform of the group field theory Lagrangian gives a relational Hamiltonian. In the classical theory, it is natural to define 'equal relational time' Poisson brackets, where 'equal time' corresponds to equal values of the scalar field clock. The quantum theory can then be defined by imposing 'equal relational time' commutation relations for the fundamental operators of the theory, with the states being elements of a Fock space with their evolution determined by the relational Hamiltonian operator. A particularly interesting family of states are condensates, as they are expected to correspond to the cosmological sector of group field theory. For the relational Hamiltonian considered in this paper, the coarse-grained dynamics of a simple type of condensate states agree exactly with the Friedmann equations in the classical limit, and also include quantum gravity corrections that ensure the big-bang singularity is replaced by a bounce.