Description

These notes arose from a series of lectures first presented at the Scuola Interna- zionale Superiore di Studi Avanzati and the International Centre for Theoretical Physics in Trieste in July 1980 and then, in an extended form, at the Universities of Sofia (1980-81) and Bielefeld (1981). Their objective has been two-fold. First, to introduce theorists with some background in group representations to the notion of twistors with an emphasis on their conformal properties; a short guide to the literature on the subject is designed to compensate in part for the imcompleteness and the one-sidedness of our review. Secondly, we present a systematic study of po- sitive energy conformal orbits in terms of twistor flag manifolds. They are interpre- ted as cl assi ca 1 phase spaces of "conformal parti cl es"; a characteri sti c property of such particles is the dilation invariance of their mass spectrum which, there fore, consists either of the point zero or of the infinite interval 222 o