FROM THE TYPE-I STRING TO M-THEORY - A CONTINUOUS CONNECTION

It is well known that the SO(32) and E-8 x E-8 heterotic strings can b e continuously connected to each other in nine dimensions, Since the s trong-coupling duals of these theories are respectively the SO(32) Typ e I theory and M-theory compactified on a line segment, there should b e a corresponding continuous connection between the Type I string and M-theory. In this paper, we give an explicit construction of this dual connecting theory. Our construction also enables us to realize the E- 8 x E-8 heterotic string as a D-string soliton of the Type I theory. T his provides a useful alternative description of the D-brane bound sta tes previously discussed from a Type I' point of view. (C) 1998 Elsevi er Science B.V.