International Center for Mathematical Modeling, Växjö University, Vejdes plats 7, 351 95 Växjö, Sweden; Andrei.Khrennikov(at)msi.vxu.se
Received 3 August 2001, accepted 26 August 2003 by K. Fredenhagen
(approx. 9 pages)
Department of Physics and Astronomy, University of Missouri-Columbia, Columbia MO 65211, USA; MashhoonB(at)missouri.edu
Received 22 August 2003, revised 11 September 2003,
accepted 11 September 2003 by F. W. Hehl
(approx. 15 pages)
Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, 80805 München, Germany; klein(at)mppmu.mpg.de
Received 3 September 2003,
accepted 13 September 2003 by F. W. Hehl
(approx. 40 pages)