Sparticle spectrum and dark matter in type I string theory with an intermediate scale

The supersymmetric particle spectrum is calculated in type I string theorie s formulated as orientifold compactifications of type IIB string theory. A string scale at an intermediate value of 10(11)-10(12) GeV is assumed and e xtra vector-like matter states are introduced to allow unification of gauge coupling constants to occur at this scale. The qualitative features of the spectrum are compared with Calabi-Yau compactification of the weakly coupl ed heterotic string and with the eleven dimensional supergravity limit of M -theory. Some striking differences are observed. Assuming that the lightest neutralino provides the dark matter in the universe, further constraints o n the sparticle spectrum are obtained. Direct detection rates for dark matt er are estimated. (C) 2000 Elsevier Science B.V. All rights reserved.