String MSSM through flipped SU(5) from Z_{12} orbifold

TL;DR

This work presents a concrete string-derived MSSM from a ${\bf Z}_{12-I}$ orbifold with flipped ${\rm SU}(5)$. By analyzing the massless spectrum from untwisted and twisted sectors, the authors obtain three ${\bf 16}_{flip}$ families and a pair of Higgs quintets, while exotics are shown to be removable at high scales through higher-order singlet VEVs, yielding a phenomenologically viable ${\cal S}$MSSM. The flipped SU(5) GUT is broken by a rank-lowering mechanism via ${\bf 10}_{1}+\overline{\bf 10}_{-1}$, and the gauge couplings can unify with $\sin^2\theta_W^0=\frac{3}{8}$ after running with exotics near the GUT scale. The model also achieves R-parity, doublet-triplet splitting, and a plausible Yukawa structure (including a top Yukawa from $T_6T_2T_4$), illustrating a concrete string-based route to the MSSM with realistic features. Overall, it demonstrates that explicit string constructions can realize a low-energy spectrum close to the MSSM with controlled exotics and realistic unification, subject to high-scale decoupling of nonessential states.

Abstract

In a $Z_{12-I}$ orbifold compactification through an intermediate flipped SU(5), the string MSSM (${\cal S}$MSSM) spectra (three families, one pair of Higgs doublets, and neutral singlets) are obtained with the Yukawa coupling structure. The GUT $\sin^2θ_W^0=\frac38$, even with exotics in the twisted sector, can be run to the observed electroweak scale value by mass parameters of vectorlike exotics near the GUT scale. We also obtain R-parity and doublet-triplet splitting.