Astronomy and Astrophysics – Astrophysics – General Relativity and Quantum Cosmology
Scientific paper
2002-10-18
Nucl.Phys. B663 (2003) 231-279
Astronomy and Astrophysics
Astrophysics
General Relativity and Quantum Cosmology
Latex,39 pages,8 figures, v3: minor changes, typos in some formulas corrected, comments added, discussion of results improved
Scientific paper
10.1016/S0550-3213(03)00378-X
We analyse the classical and quantum geometry of the Barrett-Crane spin foam model for four dimensional quantum gravity, explaining why it has to be considering as a covariant realization of the projector operator onto physical quantum gravity states. We discuss how causality requirements can be consistently implemented in this framework, and construct causal transiton amplitudes between quantum gravity states, i.e. realising in the spin foam context the Feynman propagator between states. The resulting causal spin foam model can be seen as a path integral quantization of Lorentzian first order Regge calculus, and represents a link between several approaches to quantum gravity as canonical loop quantum gravity, sum-over-histories formulations, dynamical triangulations and causal sets. In particular, we show how the resulting model can be rephrased within the framework of quantum causal sets (or histories).
Livine Etera R.
Oriti Daniele
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