http://arxiv.org/abs/1604.06023
Recent years have seen great progress towards deriving quantum cosmology models from the effective dynamics of condensate states in group field theory (GFT), where ‘cosmology is the hydrodynamics of quantum gravity’; the classical Friedmann dynamics for homogeneous, isotropic universes, as well as loop quantum cosmology (LQC) corrections to general relativity have been shown to emerge from fundamental quantum gravity. We take one further step towards strengthening the link with LQC and show, in a rather wide class of GFT models for gravity coupled to a free massless scalar field and for generic initial conditions, that GFT condensates dynamically reach a low spin phase of many quanta of geometry, in which all but an exponentially small number of quanta are characterised by a single spin $j_0$ (i.e. by a constant volume per quantum). In one particular simple and natural case, this spin is the lowest one, $j_0=1/2$. The type of quantum state usually assumed in the derivation of LQC is hence derived from the quantum dynamics of GFT, and shown to be generic. As the low spin regime is reached, the dynamics of the total volume follows precisely the classical Friedmann equations. The latter result confirms and extends recent results by Oriti, Sindoni and Wilson-Ewing in the same setting.
S. Gielen
Thu, 21 Apr 16
42/61
Comments: 14 pages, revtex
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