A COSMOLOGICAL CONSTANT WITH D⁴ xS¹ xM⁵COMPACTIFICATION OF CHIRAL CLOSED STRING

A cosmological constant has been derived from compactification of chiral closed-string. The (3+l)-dimensional space-time D⁴ has de-Sitter or anti-de-Sitter geometry. The compact space M⁵ is a Einstein manifold or a hyperbolic manifold. Some properties about tachyon and massless ghost have been discussed.