Author(s): Ichiro Oda
-- hep-th/0008012 was replaced with a revised version
on Wed, 1 Nov 2000 06:25:19 GMT (16kb) --
Paper: hep-th/0008012
Comments: 17 pages, LaTex 2e, revised version (to appear in Phys. Rev. D)
Report-no: EDO-EP-31
URL: http://arXiv.org/abs/hep-th/0008012