Ultraviolet Finite Quantum Field Theory on Quantum Spacetime

 We discuss a formulation of quantum field theory on quantum space time where the perturbation expansion of the S-matrix is term by term ultraviolet finite. The characteristic feature of our approach is a quantum version of the Wick product at coinciding points: the differences of coordinates q _j −q _k are not set equal to zero, which would violate the commutation relation between their components. We show that the optimal degree of approximate coincidence can be defined by the evaluation of a conditional expectation which replaces each function of q _j −q _k by its expectation value in optimally localized states, while leaving the mean coordinates invariant. The resulting procedure is to a large extent unique, and is invariant under translations and rotations, but violates Lorentz invariance. Indeed, optimal localization refers to a specific Lorentz frame, where the electric and magnetic parts of the commutator of the coordinates have to coincide [11]. Employing an adiabatic switching, we show that the S-matrix is term by term finite. The matrix elements of the transfer matrix are determined, at each order in the perturbative expansion, by kernels with Gaussian decay in the Planck scale. The adiabatic limit and the large scale limit of this theory will be studied elsewhere. Received: 15 January 2003 / Accepted: 20 March 2003 Published online: 5 May 2003 RID="*" ID="*" Research supported by MIUR and GNAMPA-INDAM RID="*" ID="*" Research supported by MIUR and GNAMPA-INDAM Communicated by H. Araki and D. Buchholz     

Quantum Geometry on Quantum Spacetime: Distance,Area and Volume Operators

We develop the first steps towards an analysis of geometry on the quantum spacetime proposed in Doplicher et al. (Commun Math Phys 172:187–220, 1995). The homogeneous elements of the universal differential algebra are naturally identified with operators living in tensor powers of Quantum Spacetime; this allows us to compute their spectra. In particular, we consider operators that can be interpreted as distances, areas, 3- and 4-volumes.     

Poincaré covariance and κ-Minkowski spacetime

A fully Poincaré covariant model is constructed as an extension of the κ-Minkowski spacetime. Covariance is implemented by a unitary representation of the Poincaré group, and thus complies with the original Wigner approach to quantum symmetries. This provides yet another example (besides the DFR model), where Poincaré covariance is realised à la Wigner in the presence of two characteristic dimensionful parameters: the light speed and the Planck length. In other words, a Doubly Special Relativity (DSR) framework may well be realised without deforming the meaning of “Poincaré covariance”.     

Twisted Covariance as a Non-Invariant Restriction of the Fully Covariant DFR Model

We discuss twisted covariance over the noncommutative spacetime algebra generated by the relations [q_q^m,q_qⁿ]=iq^mn{[q_\theta^\mu,q_\theta^\nu]=i\theta^{\mu\nu}} , where the matrix θ is treated as fixed (not a tensor), and we refrain from using the asymptotic Moyal expansion of the twists.