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The Spin-Foam Approach to Quantum Gravity [PDF]
Living Reviews in Relativity, 2013 This article reviews the present status of the spin-foam approach to the quantization of gravity. Special attention is payed to the pedagogical presentation of the recently-introduced new models for four-dimensional quantum gravity.
Alejandro Perez
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Spin Foams and Canonical Quantization [PDF]
Symmetry, Integrability and Geometry: Methods and Applications, 2012 This review is devoted to the analysis of the mutual consistency of the spin foam and canonical loop quantizations in three and four spacetime dimensions.
Sergei Alexandrov +2 more
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Spin foams and noncommutative geometry [PDF]
Classical and Quantum Gravity, 2010 We extend the formalism of embedded spin networks and spin foams to include topological data that encode the underlying three-manifold or four-manifold as a branched cover. These data are expressed as monodromies, in a way similar to the encoding of the gravitational field via holonomies.
Domenic Denicola +5 more
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Positivity of spin foam amplitudes [PDF]
Classical and Quantum Gravity, 2002 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. As a corollary,
John C. Baez, J. Daniel Christensen
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Spin foams as Feynman diagrams [PDF]
2001: A Relativistic Spacetime Odyssey, 2000 It has been recently shown that a certain non-topological spin foam model can be obtained from the Feynman expansion of a field theory over a group. The field theory defines a natural ``sum over triangulations'', which removes the cut off on the number of degrees of freedom and restores full covariance.
Michael Reisenberger, Carlo Rovelli
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The Hessian in Spin Foam Models [PDF]
Annales Henri Poincaré, 2019 Abstract We fill one of the remaining gaps in the asymptotic analysis of the vertex amplitudes of the Engle–Pereira–Rovelli–Livine (EPRL) spin foam models: We show that the Hessian is nondegenerate for the stationary points that corresponds to geometric nondegenerate 4 simplices. Our analysis covers the case when all faces are spacelike.
Wojciech KAMIŃSKI +3 more
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Spin angular momentum modulation via spin–orbit interaction in fractional orbital angular momentum beams [PDF]
NanophotonicsLight exhibits both spin and orbital angular momentum (SAM and OAM). These two forms of angular momentum remain independent in paraxial fields, but become coupled in confined fields through spin–orbit interactions (SOI).
Chen Xusheng +4 more
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, 2016 I discuss how to impose causality on spin-foam models, separating forward and backward propagation, turning a given triangulation to a 'causal set', and giving asymptotically the exponential of the Regge action, not a cosine. I show the equivalence of the prescriptions which have been proposed to achieve this.
Giorgio Immirzi
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Loop quantum cosmology and spin foams [PDF]
Physics Letters B, 2009 Loop quantum cosmology (LQC) is used to provide concrete evidence in support of the general paradigm underlying spin foam models (SFMs). Specifically, it is shown that: i) the physical inner product in the timeless framework equals the transition amplitude in the deparameterized theory; ii) this quantity admits a %convergent vertex expansion a la SFMs ...
Abhay Ashtekar +2 more
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The Construction of Spin Foam Vertex Amplitudes [PDF]
Symmetry, Integrability and Geometry: Methods and Applications, 2013 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.
Eugenio Bianchi, Frank Hellmann
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