Standard-like models with broken supersymmetry from type-I string vacua

We construct D = 4 type-I vacua with massless content remarkably close to t hat of the standard model of particle physics. They are tachyon-free non-su persymmetric models which are obtained starting with a standard D = 4, N = 1 compact type-IIB orientifold and adding the same number of Dp-branes and anti-Dp-branes distributed at different points of the underlying orbifold. Supersymmetry-breaking is felt by the observable world either directly, by gravity mediation or gauge mediation, depending on the brane configuration. We construct several simple three generation examples with the gauge group of the standard model or its left-right symmetric extensions. The models c ontain a number of U(1) gauge groups whose anomalies are cancelled by a gen eralized Green-Schwarz mechanism. These U(1)'s are broken but may survive a s global symmetries providing for a flavour structure to the models. The va lue of the string scale may be lowered down to the intermediate scale (as r equired in the gravity mediation case) or down to 1-100 TeV for the non-SUS Y models. Thus the present models are the first semirealistic string vacua realizing the possibility of a low string scale. The unbalanced force betwe en the pairs of Dp- and anti-Dp-branes provides for an effect which tends t o compactify some of the extra dimensions but no others. This could provide a new mechanism for radius stabilization.