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2018
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.
2000
A search for the uni cation of quantum theory and gravity has forced mathematical physicists to re-evaluate the meaning of geometry itself. The surprising answer has led to an explosion of research papers, a vast collection of examples, and to revolutions in at least three branches of pure mathematics. It o¬ers insights into the origin of the universe and the nature of physical reality.
Journal of Geometry and Physics, 1989
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.
Journal of Mathematical Physics, 2000
Quantum groups emerged in the latter quarter of the 20th century as, on the one hand, a deep and natural generalisation of symmetry groups for certain integrable systems, and on the other as part of a generalisation of geometry itself powerful enough to make sense in the quantum domain. Just as the last century saw the birth of classical geometry, so the present century sees at its end the birth of this quantum or noncommutative geometry, both as an elegant mathematical reality and in the form of the first theoretical predictions for Planck-scale physics via ongoing astronomical measurements. Noncommutativity of spacetime, in particular, amounts to a postulated new force or physical effect called cogravity.
2008
This dissertation is based on research done at the Mathematical Physics sector of the International School for Advanced Studies of Trieste, during the period from October 2003 to June 2007. It is divided into two parts: the first part (Chapters 1-2) is an account of the general theory and a collection of some general notions and results; the second part (Chapters 3-5) contains the original work, carried out under the supervision of Prof. Ludwik D abrowski and Prof. Giovanni Landi. Part of the original material presented here has been published or submitted as a preprint in the following papers:
2018
This paper introduces some basic ideas and formalism of physics in non-commutative geometry. My goals are three-fold: first to introduce the basic formal and conceptual ideas of non-commutative geometry, and second to raise and address some philosophical questions about it. Third, more generally to illuminate the point that deriving spacetime from a more fundamental theory requires discovering new modes of `physically salient' derivation.
Journal of Physics A: Mathematical and General, 1996
A finite set can be supplied with a group structure which can then be used to select (classes of) differential calculi on it via the notions of left-, right-and bicovariance. A corresponding framework has been developed by Woronowicz, more generally for Hopf algebras including quantum groups. A differential calculus is regarded as the most basic structure needed for the introduction of further geometric notions like linear connections and, moreover, for the formulation of field theories and dynamics on finite sets. Associated with each bicovariant first order differential calculus on a finite group is a braid operator which plays an important role for the construction of distinguished geometric structures. For a covariant calculus, there are notions of invariance for linear connections and tensors. All these concepts are explored for finite groups and illustrated with examples. Some results are formulated more generally for arbitrary associative (Hopf) algebras. In particular, the problem of extension of a connection on a bimodule (over an associative algebra) to tensor products is investigated, leading to the class of 'extensible connections'. It is shown that invariance properties of an extensible connection on a bimodule over a Hopf algebra are carried over to the extension. Furthermore, an invariance property of a connection is also shared by a 'dual connection' which exists on the dual bimodule (as defined in this work).
2002
We discuss the construction of finite noncommutative geometries on Hopf algebras and finite groups in the 'quantum groups approach'. We apply the author's previous classification theorem, implying that calculi in the factorisable case correspond to blocks in the dual, to classify differential calculi on the quantum codouble D * (G) = kG>◭k(G) of a finite group G. We give D * (S 3) as an example including its exterior algebra and lower cohomology. We also study the calculus on D * (A) induced from one on a general Hopf algebra A in general and specialise to D * (G) = U (g)>◭k[G] as a noncommutative isometry group of an enveloping algebra U (g) as a noncommutative space.
Czechoslovak Journal of Physics, 2003
Journal of Mathematical Physics, 2008
Journal of Geometry and Physics, 1993
This is an introduction to the old and new concepts of non-commutative (N.C.) geometry. We review the ideas underlying N.C. measure and topology, N.C. differential calculus, N.C. connections on N.C. vector bundles, and N.C. Riemannian geometry by following A. Connes' point of view.
Quantum Groups and Lie Theory, 2002
We outline the recent classification of differential structures for all main classes of quantum groups. We also outline the algebraic notion of 'quantum manifold' and 'quantum Riemannian manifold' based on quantum group principal bundles, a formulation that works over general unital algebras.
Toward a New Understanding of Space, Time and Matter, 2009
We provide a self-contained introduction to the quantum group approach to noncommutative geometry as the next-to-classical effective geometry that might be expected from any successful quantum gravity theory. We focus particularly on a thorough account of the bicrossproduct model noncommutative spacetimes of the form [t, xi] = ıλxi and the correct formulation of predictions for it including a variable speed of light. We also study global issues in the Poincaré group in the model with the 2D case as illustration. We show that any off-shell momentum can be boosted to infinite negative energy by a finite Lorentz transformaton.
Particles and Fields: Proceedings of the X Jorge André Swieca Summer School, 1999
Quantum Gravity Mathematical Models and Experimental Bounds, 2007
This is a self-contained introduction to quantum Riemannian geometry based on quantum groups as frame groups, and its proposed role in quantum gravity. Much of the article is about the generalisation of classical Riemannian geometry that arises naturally as the classical limit; a theory with nonsymmetric metric and a skew version of metric compatibilty. Meanwhile, in quantum gravity a key ingredient of our approach is the proposal that the differential structure of spacetime is something that itself must be summed over or 'quantised' as a physical degree of freedom. We illustrate such a scheme for quantum gravity on small finite sets.
arXiv (Cornell University), 2022
In this paper, we revise the concept of noncommutative vector fields introduced previously in [1, 2], extending the framework, adding new results and clarifying the old ones. Using appropriate algebraic tools certain shortcomings in the previous considerations are filled and made more precise. We focus on the correspondence between so-called Cartan pairs and first-order differentials. The case of free bimodules admitting more friendly "coordinate description" and their braiding is considered in more detail. Bimodules of right/left universal vector fields are explicitly constructed.
Classical and Quantum Gravity, 2005
Journal of Noncommutative Geometry, 2014
We discuss generalizations of the notion of i) the group of unitary elements of a (real or complex) finite dimensional C * -algebra, ii) gauge transformations and iii) (real) automorphisms, in the framework of compact quantum group theory and spectral triples. The quantum analogue of these groups are defined as universal (initial) objects in some natural categories. After proving the existence of the universal objects, we discuss several examples that are of interest to physics, as they appear in the noncommutative geometry approach to particle physics: in particular, the C * -algebras M n (R), M n (C) and M n (H), describing the finite noncommutative space of the Einstein-Yang-Mills systems, and the algebras A F = C⊕H⊕M 3 (C) and A ev = H ⊕ H ⊕ M 4 (C), that appear in Chamseddine-Connes derivation of the Standard Model of particle physics minimally coupled to gravity. As a byproduct, we identify a "free" version of the symplectic group Sp(n) (quaternionic unitary group).
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