Chapter 1 Extra Dimensions

We begin with a discussion of a model with a flat extra dimension which addresses the flavor hierarchy of the Standard Model (SM) using profiles for the SM fermions in the extra dimension. We then show how flavor violation and contributions to the electroweak precision tests can be suppressed [even with O(TeV) mass scale for the new particles] in this framework by suitable modifications to the basic model. Finally, we briefly discuss a model with a warped extra dimension in which all the SM fields propagate and we sketch how this model “mimics” the earlier model in a flat extra dimension. In this process, we outline a “complete” model addressing the Planck-weak as well as the flavor hierarchy problems of the SM.