2016/02/29 by Daniele Oriti, Lorenzo Sindoni, Edward Wilson-Ewing · 1 citation
Physics and Astronomy · #Black Holes and Theoretical Physics #Friedmann equations #General relativity #Gravitation #Isotropy #Noncommutative and Quantum Gravity Theories #Quantum #Quantum Electrodynamics and Casimir Effect #Quantum fluctuation #Quantum gravity #Scalar (mathematics) #Scalar field #gr-qc #hep-th
paper · pdf · doi:10.1088/0264-9381/33/22/224001
published as Class.Quant.Grav.33:224001,2016 · 59 pages
openalex created_date 2016/06/24 · openalex publication_date 2016/10/20 · arxiv created 2016/10/24 · arxiv updated 2016/11/23 · openalex updated_date 2026/08/05
We study the effective cosmological dynamics, emerging as the hydrodynamics of simple condensate states, of a group field theory (GFT) model for quantum gravity coupled to a massless scalar field and reduced to its isotropic sector. The quantum equations of motion for these GFT condensate states are given in relational terms with respect to the scalar field, from which effective dynamics for spatially flat, homogeneous and isotropic space–times can be extracted. The result is a generalisation of the Friedmann equations, including quantum gravity modifications, in a specific regime of the theory corresponding to a Gross–Pitaevskii approximation where interactions are subdominant. The classical Friedmann equations of general relativity are recovered in a suitable semi-classical limit for some range of parameters of the microscopic dynamics. An important result is that the quantum geometries associated with these GFT condensate states are non-singular: a bounce generically occurs in the Planck regime. For some choices of condensate states, these modified Friedmann equations are very similar to those of loop quantum cosmology.