Quarks and Leptons From Orbifolded Superstring

Using the successful standard model of particle physics but without clear guidance beyond it, it is a di? cult task to write a physics book beyond the standard model from a phenomenological point of view. At present, there is no major convincing inner space related experimental evidence against the standard model. The neutrino oscillation phenomena can be considered part of it by including a singlet ? eld in the spectrum. Only the outer space - servations on matter asymmetry, dark matter, and dark energy hint at the phenomenological need for an extension; however, there has been theoretical need for almost three decades, chie? y because of the gauge hierarchy problem in the standard model. Thus, it seems that going beyond the standard model hinges on the des- ability of resolving the hierarchy problem. At the ? eld theory level, it is fair to say that the hierarchy problem is not as desperate as the nonrenormalizab- ity problem present in the old V–A theory of weak interactions on the road to the standard model. An extension beyond the standard model can easily be ruled out as witnessed in the case of technicolor. However, a consistent framework with supersymmetry for a resolution of the hierarchy problem has been around for a long time. Even its culprit “superstring” has been around for twenty years, and the most remarkable thing about this supersymmetric extension is that it is still alive.