## Zero-slope limit of the compactified closed bosonic string

We investigate, in the low-energy limit of the closed bosonic string theory, the role of the toroidal compactification, in which the extra spatial coordinates are circular with radius [ital R]. We explicitly show that the double limit [alpha][prime][r arrow]0 and [ital R][r arrow]0, performed on the tree scattering amplitude of four massless scalar particles, leads to four-dimensional amplitudes describing a diffusion due to the exchange of a scalar, spin-1, and spin-2 particle and that it is not influenced by the compactification procedure adopted.