The plausible relativistic physical variables describing a spinning, charged and massive particle are, besides the charge itself, its Minkowski (four) po sition X, its relativistic linear (four) momentum P and also its so-called Lorentz (four) angular momentum E # 0, the latter forming four trans lation invariant part of its total angular (four) momentum M. Expressing these variables in terms of Poincare covariant real valued functions defined on an extended relativistic phase space [2, 7J means that the mutual Pois son bracket relations among the total angular momentum functions Mab and the linear momentum functions pa have to represent the commutation relations of the Poincare algebra. On any such an extended relativistic phase space, as shown by Zakrzewski [2, 7], the (natural?) Poisson bracket relations (1. 1) imply that for the splitting of the total angular momentum into its orbital and its spin part (1. 2) one necessarily obtains (1. 3) On the other hand it is always possible to shift (translate) the commuting (see (1. 1)) four position xa by a four vector ~Xa (1. 4) so that the total angular four momentum splits instead into a new orbital and a new (Pauli-Lubanski) spin part (1. 5) in such a way that (1. 6) However, as proved by Zakrzewski [2, 7J, the so-defined new shifted four a position functions X must fulfill the following Poisson bracket relations: (1.

For more than 70 years, quantum field theory (QFT) can be seen as a driving force in the development of theoretical physics. The developed ideas and techniques of QFT have been successfully applied, in particular, within the phenomenological description of particle physics and solid state physics. Equally fascinating is the fruitful impact which QFT had in rather remote areas of mathematics, like Gromov-Witten and Donaldson-Witten invariants of low dimensional manifolds and for modular forms in relation to string theory. More recent developments in QFT also attack the problem to formulate a quantum version of gravity. However, there is no 'QFT as such', but instead there are only various mathematical approaches, aiming to make the basic ideas of QFT more rigorous. Such a rigorous understanding seems indispensable, in particular, to get a better understanding of how a physically reasonable quantum theory of gravity may look like.

The present book features some of the different approaches, different physical viewpoints and techniques used to make the notion of quantum field theory more precise. This concerns algebraic, analytic, geometric, and stochastic aspects. For example, there will be discussed deformation theory, and the holographic AdS/CFT correspondence. The book also contains more recent developments like the use of category theory and topos theoretic methods to describe QFT. This volume emerged from the 3rd 'Blaubeuren Workshop: Recent Developments in Quantum Field Theory', held in July 2007 at the Max Planck Institute of Mathematics in the Sciences in Leipzig/Germany. All of the contributions to the volume are peer reviewed and committed to the idea of this workshop series: 'To bring together outstanding experts working in the field of mathematics and physics to discuss in an open atmosphere the fundamental questions at the frontier of theoretical physics'.

The first part of a two-volume set concerning the field of Clifford (geometric) algebra, this work consists of thematically organized chapters that provide a broad overview of cutting-edge topics in mathematical physics and the physical applications of Clifford algebras. This volume is devoted specifically to the mathematical aspects of Clifford algebras and their applications in physics. Algebraic geometry, cohomology, non-communicative spaces, "q"-deformations and the related quantum groups, and projective geometry provide the basis for algebraic topics covered. Physical applications and extensions of physical theories such as the theory of quaternionic spin, a projective theory of hadron transformation laws, and electron scattering are also presented, showing the broad applicability of Clifford geometric algebras in solving physical problems. Treatment of the structure theory of quantum Clifford algebras, the connection to logic, group representations, and computational techniques including symbolic calculations and theorem proving rounds out the presentation.