A POSSIBLE NEW DIMENSION AT A FEW TEV

We examine the possibility of the existence of a large internal dimension at relatively low energies of the order of a few TeV. Such a dimension is a general prediction of perturbative string theories, which relate its size to the supersymmetry breaking scale. We point out that, contrary to our naive expectations, this scenario is consistent with perturbative unification up to the Planck scale, in a particular class of "four"-dimensional string models. Furthermore, it has spectacular phenomenological consequences, whose main effects are discussed. © 1990.