Using Z3 asymmetric orbifolds in heterotic string theory, we construct N=1 SUSY three-generation models with the standard model gauge group SU(3)_C times SU(2)_L times U(1)_Y and the left-right symmetric group SU(3)_C times SU(2)_L times SU(2)_R times U(1)_{B-L}. One of the models possesses a gauge flavor symmetry for the Z3 twisted matter.
We search for realistic supersymmetric standard-like models from SO(32) heterotic string theory on factorizable tori with multiple magnetic fluxes. Three chiral ganerations of quarks and leptons are derived from the adjoint and vector representations
of SO(12) gauge groups embedded in SO(32) adjoint representation. Massless spectra of our models also include Higgs fields, which have desired Yukawa couplings to quarks and leptons at the tree-level.
We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N=1 super Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show po
ssible patterns of Yukawa matrices. Some examples of numerical studies are also shown.
Recently it was proposed that the ten dimensional tachyonic superstring vacua may serve as good starting points for the construction of viable phenomenological models. Such phenomenologically viable models enlarge the space of possible string solutio
ns, and may offer novel insight into some of the outstanding problems in string phenomenology. In this paper we present a three generation standard--like model that may be regarded as a compactification of a ten dimensional tachyonic vacuum. We discuss the features of the model as compared to a similar model that may be regarded as compactification of the ten dimensional $SO(16)times SO(16)$ heterotic-string. We further argue that in the four dimensional model all the geometrical moduli are fixed perturbatively, whereas the dilaton may be fixed by hidden sector non--perturbative effects.
Grand unification groups (GUTs) are constructed from SO(32) heterotic string via $Z_{12-I}$ orbifold compactification. So far, most phenomenological studies from string compactification relied on $EE8$ heterotic string, and this invites the SO(32) he
terotic string very useful for future phenomenological studies. Here, spontaneous symmetry breaking is achieved by Higgsing of the anti-symmetric tensor representations of SU($N$). The anti-SU($N$) presented in this paper is a completely different class from the flipped-SU($N$)s from the spinor representations of SO($2N$). Here, we realize chiral representations: $tsixoplus 5cdot ineb $ for a SU(9) GUT and $3{{ten}_Loplus {fiveb}_L}$ for a SU(5)$$ GUT. In particular, we confirm that the non-Abelian anomalies of SU(9) gauge group vanish and hence our compactification scheme achieves the key requirement. We also present the Yukawa couplings, in particular for the heaviest fermion, $t$, and lightest fermions, neutrinos. In the supersymmetric version, we present a scenario how supersymmetry can be broken dynamically via the confining gauge group SU(9). Three families in the visible sector are interpreted as the chiral spectra of SU(5)$$ GUT.
From the string partition function, we discuss the mass-shell and GSO projection conditions valid for Kaluza-Klein (KK) as well as massless states in the heterotic string theory compactified on a nonprime orbifold. Based on the obtained conditions we
construct a 4D string standard model, which is embedded in a 6D SUSY GUT by including KK states above the compactification scale. We discuss the stringy threshold corrections to gauge couplings, including the Wilson line effects.