Orbifold phenomenology

In this chapter, we review several attempts toward obtaining a supersymmetric standard model from the E₈ × E′₈ heterotic string and some phenomenological implications. In Chaps. 6-9, we discussed in length the theoretical framework for orbifolded superstrings. We restricted our discussion to the E₈ × E′₈ heterotic string, chiefly because breaking the chain of E₈ down to the SU(5) or SU(3)³ goes through the intermediate 27 of E₆. This is an important observation since the fifteen chiral fields (2.8) of the standard model(SM) are contained in the fundamental 27 of E₆ or in the spinor 16 of SO(10). By restricting ourselves to only this chain, we can automatically achieve the correct charge assignments, coming from 16 of SO(10). On the other hand, if the intermediate step cannot contain 27 of E₆, it is most probable that exotically charged particles(exotics) would appear. But this argument utilizes matter only from the untwisted sector. For twisted sector matter, SO(32) breaking can be useful as commented in Sect. 10.4.