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General Relativity and Quantum Cosmology, gr-qc,High Energy Physics - Theory, hep-th
Abstract:
We study the effective cosmological dynamics, emerging as the hydrodynamics
of simple condensate states, of a group field theory model for quantum gravity
coupled to a massless scalar field and reduced to its isotropic sector. The
quantum equations of motion for these group field theory 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 generalization of the Friedmann equations,
including quantum gravity modifications, in a specific regime of the theory.
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.
