A proposal for analysing the classical limit of kinematic loop gravity

Abstract

We analyse the classical limit of kinematic loop quantum gravity in which the diffeomorphism and Hamiltonian constraints are ignored. We show that there are no quantum states in which the primary variables of the loop approach, namely the SU(2) holonomies along all possible loops, approximate their classical counterparts. At most a countable number of loops must be specified. To preserve spatial covariance, we choose this set of loops to be based on physical lattices specified by the quasiclassical states themselves. We construct `macroscopic' operators based on such lattices and propose that these operators be used to analyse the classical limit. Thus, our aim is to approximate classical data using states in which appropriate macroscopic operators have low quantum fluctuations.

Although, in principle, the holonomies of `large' loops on these lattices could be used to analyse the classical limit, we argue that it may be simpler to base the analysis on an alternate set of `flux'-based operators. We explicitly construct candidate quasiclassical states in two spatial dimensions and indicate how these constructions may generalize to three dimensions. We discuss the less robust aspects of our proposal with a view towards possible modifications. Finally, we show that our proposal also applies to the diffeomorphism-invariant Rovelli model which couples a matter reference system to the Hussain-Kucha{r} model.