U-duality (sub-)groups and their topology

Abstract

We discuss some consequences of the fact that symmetry groups appearing in compactified (super-)gravity may be non-simply connected. The possibility to add fermions to a theory results in a simple criterion to decide whether a 3-dimensional coset sigma model can be interpreted as a dimensional reduction of a higher dimensional theory. Similar criteria exist for higher dimensional sigma models, though less decisive. Careful examination of the topology of symmetry groups rules out certain proposals for M-theory symmetries, which are not ruled out at the level of the algebra's. We conclude with an observation on the relation between the ``generalized holonomy'' proposal, and the actual symmetry groups resulting from E_10 and E_11 conjectures.

LaTeX, 8 pages, 2 tables, 1 figure, uses IOP-style files. Contributed to the proceedings of the RTN-workshop ``The quantum structure of space-time and the geometrical nature of the fundamental interactions,'', Copenhagen, Denmark, september 2003