Yoshiharu Kawamura

Triplet-Doublet Splitting, Proton Stability and an Extra Dimension

We propose a new possibility to reconcile the coupling unification scenario with the triplet-doublet mass splitting based on a 5-dimensional supersymmetric model with SU(5) gauge symmetry. It is shown that the minimal supersymmetric standard model is derived on a 4-dimensional wall through compactification on S 1 /(Z2 × Z � 2). In this paper, we propose a new possibility to reconcile the coupling unification scenario with the triplet-doublet mass splitting. The coupling unification originates from the existence of a unified gauge symmetry, G, in a high-energy theory on a higher-dimensional space-time. The full symmetry is not realized in the low-energy physics, where light particles play an essential role. The symmetry G is reduced by the presence of non-universal values of the intrinsic parity on a compact space among components in each multiplet of G. We show that the SUSY part of the Lagrangian in the MSSM is derived on a 4-dimensional (4D) wall through compactification upon the orbifold S 1 /(Z2 × Z � 2), with a suitable assignment of Z2 × Z � 2 parity, from a 5D SUSY model based on G = SU(5). No particles appear other than the MSSM particles in the massless state, and the triplet-doublet mass splitting is realized by the Z2 × Z � 2 projection. We also discuss proton stability in our model.

Gauge Symmetry Reduction from the Extra Space S1/Z2

We study a mechanism of symmetry transition upon compactification of a 5-dimensional field theory on

Split Multiplets, Coupling Unification and an Extra Dimension

S^1/Z_2

ZN orbifold models

. The transition occurs unless all components in a multiplet of a symmetry group have a common

Low-energy efFective Lagrangian in unified theories with nonuniversal supersymmetry-breaking terms

Z_2

Dynamical rearrangement of gauge symmetry on the orbifold S1/Z2

parity on

Soft scalar masses in string models with anomalous U(1) symmetry

S^1/Z_2

Probing the symmetry-breaking pattern using sfermion masses

. This mechanism is applied to a reduction of SU(5) gauge symmetry in grand unified theory, and phenomenological implications are discussed.

Generic formula of soft scalar masses in string models

We study a gauge coupling unification scenario based on a non-supersymmetric 5-dimensional model. Through an orbifold compactification, we obtain the Standard Model with split multiplets on a 4-dimensional wall, which is compatible with a grand unification.

Phenomenological constraints on SUSY SU(5) GUTs with nonuniversal gaugino masses

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.