Probing Minimal 5D Extensions of the Standard Model: From LEP to an e^+e^- Linear Collider

We derive new improved constraints on the compactification scale of minimal 5-dimensional (5D) extensions of the Standard Model (SM) from electroweak and LEP2 data and estimate the reach of an e^+e^- linear collider such as TESLA. Our analysis is performed within the framework of non-universal 5D models, where some of the gauge and Higgs fields propagate in the extra dimension, while all fermions are localized on a S^1/Z_2 orbifold fixed point. Carrying out simultaneous multi-parameter fits of the compactification scale and the SM parameters to the data, we obtain lower bounds on this scale in the range between 4 and 6 TeV. These fits also yield the correlation of the compactification scale with the SM Higgs mass. Investigating the prospects at TESLA, we show that the so-called GigaZ option has the potential to improve these bounds by about a factor 2 in almost all 5D models. Furthermore, at the center of mass energy of 800 GeV and with an integrated luminosity of 10^3 fb^-1, linear collider experiments can probe compactification scales up to 20-30 TeV, depending on the control of systematic errors.