Abstract
The free fermionic construction of the heterotic string in four dimensions produced a large space of three-generation models with the underlying embedding of the Standard Model states. The symmetry is broken to a subgroup directly at the string scale. Over the past few years free fermionic models with the Pati-Salam and flipped subgroups have been classified. In this paper we extend this classification program to models in which the symmetry is broken at the string level to the (SU421) subgroup. The subspace of free fermionic models that we consider corresponds to symmetric orbifolds. We provide a general argument that shows that this class of SU421 free fermionic models cannot produce viable three-generation models.
- Received 18 January 2015
DOI:https://doi.org/10.1103/PhysRevD.91.066006
© 2015 Published by the American Physical Society