منابع مشابه
Positivity of Spin Foam Amplitudes
The amplitude for a spin foam in the Barrett–Crane model of Riemannian quantum gravity is given as a product over its vertices, edges and faces, with one factor of the Riemannian 10j symbols appearing for each vertex, and simpler factors for the edges and faces. We prove that these amplitudes are always nonnegative for closed spin foams. This means one can use the Metropolis algorithm to comput...
متن کاملThe Construction of Spin Foam Vertex Amplitudes
Spin foam vertex amplitudes are the key ingredient of spin foam models for quantum gravity. These fall into the realm of discretized path integral, and can be seen as generalized lattice gauge theories. They can be seen as an attempt at a 4-dimensional generalization of the Ponzano–Regge model for 3d quantum gravity. We motivate and review the construction of the vertex amplitudes of recent spi...
متن کاملSpin Foam Models
While the use of spin networks has greatly improved our understanding of the kinematical aspects of quantum gravity, the dynamical aspects remain obscure. To address this problem, we deene the concept of a `spin foam' going from one spin network to another. Just as a spin network is a graph with edges labeled by representations and vertices labeled by intertwining operators, a spin foam is a 2-...
متن کاملSpin Foam Perturbation Theory
We study perturbation theory for spin foam models on triangulated manifolds. Starting with any model of this sort, we consider an arbitrary perturbation of the vertex amplitudes, and write the evolution operators of the perturbed model as convergent power series in the coupling constant governing the perturbation. The terms in the power series can be efficiently computed when the unperturbed mo...
متن کاملCausality in Spin Foam Models
We compute Teitelboim’s causal propagator in the context of canonical loop quantum gravity. For the Lorentzian signature, we find that the resultant power series can be expressed as a sum over branched, colored two-surfaces with an intrinsic causal structure. This leads us to define a general structure which we call a “causal spin foam”. We also demonstrate that the causal evolution models for ...
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ژورنال
عنوان ژورنال: Classical and Quantum Gravity
سال: 2002
ISSN: 0264-9381,1361-6382
DOI: 10.1088/0264-9381/19/8/316