Noriyasu Ohtsubo

ZN orbifold models

ZN orbifolds are studied because of the possibility to dispose of six extra dimensions of E8×E′8 heterotic string theory and in order to obtain a realistic effective low-energy theory. All the independent embeddings of ZN rotations are classified using both procedures with shifts and rotations of an E8×E8 root lattice. SU5×U14×(Hidden Gauge Group) models are elucidated as examples among the models obtained. It is explained how the ZN orbifold models are modified when the Wilson-line mechanism turns on by making use of an example of a semi-standard model derived from the Z7 orbifold.

Geometrical aspects of Z(N) orbifold phenomenology

We study the geometrical and phenomenological aspects of ZN orbifold models. Conditions on the background moduli and Wilson lines are clarified. We investigate the explicit ZN-invariant states through a modified GSO projection and calculate Yukawa coupling conditions due to space-group and SO(10) invariance. We estimate a contribution of a holomorphic instanton to the couplings.

Yukawa coupling condition of ZN orbifold models

Abstract Yukawa coupling conditions of Z N orbifold models are studied. We obtain physical states of Z N orbifold models explicitly. The selection rule of the space group and SO(10) invariance are investigated.

Gauge Groups of ZN Orbifold Models

Z_N orbifold models which have N=1 space-time supersymmetry are cxamined. All gauge groups of Z_N orbifold models are classified completely.

Z4 and Z6 orbifold models

Abstract Z4 and Z6 models with abelian embeddings are studied. The complete classification of gauge groups and matter fields is given. There exist 12, 58 and 61 models in Z4, Z6-I and Z6-II orbifold models, respectively.

Minimal string unification and constraint on hidden sector

We examine whether a minimal string model possessing the same massless spectra as the MSSM can be obtained from

Allowed Yukawa couplings of ZN×ZM orbifold models

Z_4

Z7 orbifold models

,

Study of minimal string unification in Z8 orbifold models

Z_6

Z8 and Z12 orbifold models

and