Data:	Mercoledì 13 Ottobre 2004, Ore 16.30
Luogo:	Aula 1101, Dip. Matematica, U. Roma "Tor Vergata"
Speaker:	Mihaly Weiner, Università di Roma "Tor Vergata"
Titolo:	UNIQUENESS OF THE STRESS-ENERGY TENSOR
Abstract:	While quantities like total energy or momentum have a clear physical meaning (and a well-established mathematical description), there are some ambiguities regarding their local distribution. For example, the requirements that the energy density should be a local quantity whose integral over space is the total energy, in the classical theory of the Electromagnetic Field do not fix a unique expression for such a density. Considering a Conformal Quantum Field Theory in 2 spacetime dimensions, or even more specifically, a chiral component of such a theory (given as a net of von Neumann algebras associated to the arcs of the unit circle together with a representation of the Moebius group), as it will be explained, the equivalent question is the following. Can there be more than one representation of the group Diff+(S1) which is compatible with the local structure, acts in a covariant manner on the net of von Neumann algebras, and is an extension of the Moebius symmetry. With the help of a new result regarding the representation theory of Diff+(S1) in the above mentioned case we prove uniqueness. Applications, such as a proof for the automatic commutation between vacuum preserving gauge symmetries and diffeomorphism symmetries, and new constructions of nets exhibiting no diffeomorphism symmetry will be also discussed in the lecture.