On the effective theory of low-scale orientifold string vacua

The effective field theory of the minimal low scale orientifold models is developed. It describes universal features of related orientifold vacua in string theory. It contains, beyond the Standard Model fields, an MSSM-like Higgs sector and three anomalous (massive) U(1) gauge bosons. All renormalizable couplings are included as well as some dimension-five couplings that are important for anomaly cancellation. The Higgs symmetry breaking induces mixing between the anomalous U(1) gauge bosons, the photon and Z0. This mixing as well as the anomaly related cubic vector boson couplings is potentially important for discriminating such models from other theories containing Zs. Some interesting tree-level processes are also evaluated.