A Fock space structure for the diffeomorphism invariant Hilbert space of loop quantum gravity and its applications

• Published in: Classical and quantum gravity Vol. 40; no. 22; pp. 225002 - 225026
• Main Authors: Sahlmann, Hanno, Sherif, Waleed
• Format: Journal Article
• Language: English
• Published: IOP Publishing 16.11.2023
• Subjects: coherent states; diffeomorphism invariance; Fock space; group field theory; loop quantum gravity
• ISSN: 0264-9381; 1361-6382
• DOI: 10.1088/1361-6382/acfb6f

Abstract Loop quantum gravity (LQG) is a quantization program for gravity based on the principles of QFT and general covariance of general relativity. Quantum states of LQG describe gravitational excitations based on graphs embedded in a spatial slice of spacetime. We show that, under certain assumptions on the class of diffeomorphisms, the space of diffeomorphism invariant states carries a Fock space structure. The role of one-particle excitations for this structure is played by the diffeomorphism invariant states based on graphs with a single (linked) component. This means, however, that a lot of the structure of the diffeomorphism invariant Hilbert space remains unresolved by this structure. We show how the Fock structure allows to write at least some condensate states of group field theory as diffeomorphism invariant coherent states of LQG in a precise sense. We also show how to construct other interesting states using this Fock structure. We finally explore the quantum geometry of single- and multi-particle states and tentatively observe some resemblance to geometries with a single or multiple components, respectively.