Affiliation: | (1) INSEAD, F-77305 Fontainebleau, France;(2) Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, USSR;(3) Present address: Dublin Institute for Advanced Studies, Dublin 4, Ireland;(4) Present address: Instituut voor Theoretische Fysica, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium |