2-D Gravity as Gauge Theories with Extended Groups

The interaction of matter with gravity in two dimensional spacetimes can be supplemented with a geometrical force analogous to a Lorentz force produced on a surface by a constant perpendicular magnetic field. In the special case of constant curvature, the relevant symmetry does not lead to the de Sitter or the Poincar'e algebra but to an extension of them by a central element. This richer structure suggests to construct a gauge theory of 2-D gravity that reproduces the Jackiw-Teitelboim model and the string inspired model. Moreover matter can be coupled in a gauge invariant fashion. Classical and quantized results are discussed. Based on a talk given at the XXIIIth International Conference on Differential Geometric Methods in Theoretical Physics. Ixtapa, Mexico. September 1993.