An Introduction to Noncommutative Geometry (original) (raw)

1997, Eprint Arxiv Physics 9709045

The lecture notes of this course at the EMS Summer School on Noncommutative Geometry and Applications in September, 1997 are now published by the EMS. Here are the contents, preface and updated bibliography from the published book. Contents 1 Commutative Geometry from the Noncommutative Point of View 1.1 The Gelfand-Naȋmark cofunctors 1.2 The Γ functor 1.3 Hermitian metrics and spin c structures 1.4 The Dirac operator and the distance formula 2 Spectral Triples on the Riemann Sphere 2.1 Line bundles and the spinor bundle 2.2 The Dirac operator on the sphere S 2 2.3 Spinor harmonics and the spectrum of D / 2.4 Twisted spinor modules 2.5 A reducible spectral triple 3 Real Spectral Triples: the Axiomatic Foundation 3.1 The data set 3.2 Infinitesimals and dimension 3.3 The first-order condition 3.4 Smoothness of the algebra 3.5 Hochschild cycles and orientation 3.6 Finiteness of the K-cycle 3.7 Poincaré duality and K-theory 3.8 The real structure Geometries on the Noncommutative Torus 4.1 Algebras of Weyl operators 4.2 The algebra of the noncommutative torus 4.3 The skeleton of the noncommutative torus 4.4 A family of spin geometries on the torus The Noncommutative Integral 5.1 The Dixmier trace on infinitesimals 5.2 Pseudodifferential operators 5.3 The Wodzicki residue 5.4 The trace theorem 5.5 Integrals and zeta residues Quantization and the Tangent Groupoid 6.1 Moyal quantizers and the Moyal deformation 6.2 Smooth groupoids 6.3 The tangent groupoid 6.4 Moyal quantization as a continuity condition 6.5 The hexagon and the analytical index 6.6 Quantization and the index theorem Equivalence of Geometries 7.1 Unitary equivalence of spin geometries 7.2 Morita equivalence and connections 7.3 Vector bundles over noncommutative tori 7.4 Morita-equivalent toral geometries 7.5 Gauge potentials Action Functionals 8.1 Algebra automorphisms and the metric 8.2 The fermionic action 8.3 The spectral action principle 8.4 Spectral densities and asymptotics Epilogue: New Directions 9.1 Noncommutative field theories 9.2 Isospectral deformations 9.3 Geometries with quantum group symmetry 9.4 Other developments

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LTCC Lectures on Noncommutative Differential Geometry

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Noncommutative geometry is the idea that when geometry is done in terms of coordinate algebras, one does not really need the algebra to be commutative. We provide an introduction to the relevant mathematics from a constructive ‘differential algebra’ point of view that works over general fields and includes the noncommutative geometry of quantum groups as well as of finite groups. We also mention applications to models of quantum spacetime.

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The structure of amanifold can be encoded in the commutative algebra of functions on the manifold it sell-this is usual-. In the case of a non com.mut.ative algebra thereis no underlying manifold and the usual concepts and tools of diffe.rential geometry (differentialforms, De Rham cohomology, vector bundles, connections, elliptic operators, index theory.. .) have to be generalized. This is the subject of non commutative differential geometry and is believed to be of fundamental importance in our understanding of quantum field theories. The presentpaper is an introduction for the non specialist and a review oftheprincipal results on the field.

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Noncommutative geometry is based on an idea that an associative algebra can be regarded as "an algebra of functions on a noncommutative space". The major contribution to noncommutative geometry was made by A. Connes, who, in particular, analyzed Yang-Mills theories on noncommutative spaces, using important notions that were introduced in his papers (connection, Chern character, etc). It was found recently that Yang-Mills theories on noncommutative spaces appear naturally in string/M-theory; the notions and results of noncommutative geometry were applied very successfully to the problems of physics.

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Contemporary Mathematics, 2011

In this paper we prove a formula for the analytic index of a basic Dirac-type operator on a Riemannian foliation, solving a problem that has been open for many years. We also consider more general indices given by twisting the basic Dirac operator by a representation of the orthogonal group. The formula is a sum of integrals over blowups of the strata of the foliation and also involves eta invariants of associated elliptic operators. As a special case, a Gauss-Bonnet formula for the basic Euler characteristic is obtained using two independent proofs.

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