A D-brane alternative to unification

We propose a minimal embedding of the Standard Model spectrum in a D-brane configuration of type I string theory. The SU(3) color and SU(2) weak inter actions arise from two different collections of branes. The model is neithe r grand unified nor supersymmetric but it naturally leads to the right pred iction of the weak angle for a string scale of the order of a few TeV. It r equires two Higgs doublets and guarantees proton stability. (C) 2000 Publis hed by Elsevier Science B.V.