Author(s): Olindo Corradini and Zurab Kakushadze
-- hep-th/0009022 was replaced with a revised version
on Wed, 1 Nov 2000 02:40:52 GMT (10kb) --
Paper: hep-th/0009022
Comments: 11 pages, revtex; a minor misprint corrected (to appear in Phys.
Lett. B)
Report-no: YITP-00-37
URL: http://arXiv.org/abs/hep-th/0009022