TeV-scale Z' bosons in intersecting D-brane SM-like models

Recent string constructions with intersecting D6 and D5 brane models succeeded in predicting in the low energy limit a symmetry group and a fermionic spectrum similar to that of the SM. In such constructions additional U(1) fields are a generic presence and they (or linear combinations thereof) become massive through a string mechanism which couples them to RR two-forms. $U(1)_Y$ of hypercharge emerges as a linear combination of the initial U(1) symmetries while the massive U(1) fields induce (through mixing with Z boson) corrections on Z mass. $\rho$ parameter constraints on the latter allow one to set lower bounds on the string scale in the TeV region. These can then be used to {\it predict} lower bounds on the masses of the additional $Z'$ bosons, without specific assumptions about the compactification volume.