A Small Cosmological Constant, Grand Unification and Warped Geometry

We will show that it is possible to obtain the observed value for the fourdimensional cosmological constant Λ4 by an exponential suppression of an initially Planck-sized constant. It is a surprising feature that the suppression-length corresponds to the GUT-scale. To make the relationship explicit, we consider a set-up consisting of two positive tension domain-walls, separated by a distance corresponding to the inverse of the GUT-scale and show how a realistic Λ4 is obtained through a warp-factor of the five-dimensional theory. It is then pointed out, that the embedding of the set-up into IIB string-theory naturally describes a spontaneously broken SU(6) SUSY GUT with interesting consequences for the doublet-triplet splitting problem of GUT-theories. Furthermore, the various hypercharge assignments of the SM matter fields arise in a simple way from a consistency argument and composition of two sorts of “basic” open string states. [email protected]