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Search Results: 1 - 10 of 229004 matches for " Joseph C. Varilly "
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An Introduction to Noncommutative Geometry
Joseph C. Varilly
Physics , 1997,
Abstract: This is the introduction and bibliography for lecture notes of a course given at the Summer School on Noncommutative Geometry and Applications, sponsored by the European Mathematical Society, at Monsaraz and Lisboa, Portugal, September 1-10, 1997. In the published version, an epilogue of recent developments and many new references from 1998-2006 have been added. 1. Commutative geometry from the noncommutative point of view. 2. Spectral triples on the Riemann sphere. 3. Real spectral triples, the axiomatic foundation. 4. Geometries on the noncommutative torus. 5. The noncommutative integral. 6. Quantization and the tangent groupoid. 7. Equivalence of geometries. 8. Action functionals. 9. Epilogue: new directions.
The interface of noncommutative geometry and physics
Joseph C. Varilly
Physics , 2002,
Abstract: The progress of noncommutative geometry has been crucially influenced, from the beginning, by quantum physics: we review this development in recent years. The Standard Model, with its central role for the Dirac operator, led to several formulations culminating in the concept of a real spectral triple. String theory then came into contact with NCG, leading to an emphasis on Moyal-like algebras and formulations of quantum field theory on noncommutative spaces. Hopf algebras have yielded an unexpected link between the noncommutative geometry of foliations and perturbative quantum field theory. The quest for a suitable foundation of quantum gravity continues to promote fruitful ideas, among them the spectral action principle and the search for a better understanding of "noncommutative spaces".
Noncommutative geometry and quantization
Joseph C. Varilly
Physics , 1999,
Abstract: We examine some recent developments in noncommutative geometry, including spin geometries on noncommutative tori and their quantization by the Shale-Stinespring procedure, as well as the emergence of Hopf algebras as a tool linking index theory and renormalization calculations
Quantum symmetry groups of noncommutative spheres
Joseph C. Varilly
Mathematics , 2001, DOI: 10.1007/s002200100490
Abstract: We show that the noncommutative spheres of Connes and Landi are quantum homogeneous spaces for certain compact quantum groups. We give a general construction of homogeneous spaces which support noncommutative spin geometries.
Hopf algebras in noncommutative geometry
Joseph C. Varilly
Mathematics , 2001,
Abstract: We give an introductory survey to the use of Hopf algebras in several problems of noncommutative geometry. The main example, the Hopf algebra of rooted trees, is a graded, connected Hopf algebra arising from a universal construction. We show its relation to the algebra of transverse differential operators introduced by Connes and Moscovici in order to compute a local index formula in cyclic cohomology, and to the several Hopf algebras defined by Connes and Kreimer to simplify the combinatorics of perturbative renormalization. We explain how characteristic classes for a Hopf module algebra can be obtained from the cyclic cohomology of the Hopf algebra which acts on it. Finally, we discuss the theory of noncommutative spherical manifolds and show how they arise as homogeneous spaces of certain compact quantum groups.
Orbifolds are not commutative geometries
Adam Rennie,Joseph C. Varilly
Mathematics , 2007,
Abstract: In this note we show that the crucial orientation condition for commutative geometries fails for the natural spectral triple of an orbifold M/G.
Reconstruction of manifolds in noncommutative geometry
Adam Rennie,Joseph C. Varilly
Mathematics , 2006,
Abstract: We show that the algebra A of a commutative unital spectral triple (A,H,D) satisfying several additional conditions, slightly stronger than those proposed by Connes, is the algebra of smooth functions on a compact spin manifold.
Dixmier traces on noncompact isospectral deformations
Victor Gayral,Bruno Iochum,Joseph C. Varilly
Mathematics , 2005,
Abstract: We extend the isospectral deformations of Connes, Landi and Dubois-Violette to the case of Riemannian spin manifolds carrying a proper action of the noncompact abelian group $R^l$. Under deformation by a torus action, a standard formula relates Dixmier traces of measurable operators to integrals of functions on the manifold. We show that this relation persists for actions of $R^l$, under mild restrictions on the geometry of the manifold which guarantee the Dixmier traceability of those operators.
Riemannian manifolds in noncommutative geometry
Steven Lord,Adam Rennie,Joseph C. Varilly
Mathematics , 2011, DOI: 10.1016/j.geomphys.2012.03.004
Abstract: We present a definition of Riemannian manifold in noncommutative geometry. Using products of unbounded Kasparov modules, we show one can obtain such Riemannian manifolds from noncommutative spin^c manifolds; and conversely, in the presence of a spin^c structure. We also show how to obtain an analogue of Kasparov's fundamental class for a Riemannian manifold, and the associated notion of Poincar\'e duality. Along the way we clarify the bimodule and first-order conditions for spectral triples.
From geometric quantization to Moyal quantization
Jose M. Gracia-Bondia,Joseph C. Varilly
Physics , 1994, DOI: 10.1063/1.531059
Abstract: We show how the Moyal product of phase-space functions, and the Weyl correspondence between symbols and operator kernels, may be obtained directly using the procedures of geometric quantization, applied to the symplectic groupoid constructed by ``doubling'' the phase space.
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