Kang-Sin Choi

Quarks and leptons from orbifolded superstring

This book is a guide for all those who want to explore the standard model using string theory. The approach pursued is “halfway” between a textbook and advanced research work and, accordingly, the book will allow both graduate students and particle phenomenologists to easily get acquainted with this fascinating field. In this new edition the authors report on the status quo of the standard model following the discovery of the Higgs Boson, as well as the latest results concerning physics beyond the standard model. They present a formal introduction to string orbifolds and explain in detail how the massless states and the Kaluza-Klein spectra can be derived from the partition function. In turn, they provide an overview of orbifold phenomenology, by introducing the key aspects of string orbifolds in the context of SUSY standard models. In closing, the authors discuss the Grand Unified Theories (GUTs) from orbifolds and share key concepts regarding Calabi-Yau compactifications, M-theory and F-theory.

Dynkin diagram strategy for orbifolding with Wilson lines

Abstract A simple method for breaking gauge groups by orbifolding is presented. We extend the method of Kac and Peterson to include Wilson lines. The complete classification of the gauge group breaking, e.g., from heterotic string, is now possible. From this Dynkin diagram technique, one can easily visualize the origin and the symmetry pattern of the surviving gauge group.

Three family Z3 orbifold trinification, MSSM and doublet–triplet splitting problem

Abstract A Z 3 orbifold compactification of E 8 × E 8 ′ heterotic string is considered toward a trinification SU (3) 3 with three light families. The GUT scale VEVs of the SU (2) W × U (1) Y × SU (3) c singlet chiral fields in two sets of the trinification spectrum allow an acceptable symmetry breaking pattern toward MSSM. We show that a doublet–triplet splitting is related to the absence of a Δ B nonzero operator.

Unification in intersecting brane models

We propose a unification scenario for supersymmetric intersecting brane models. The quarks and leptons are embedded into adjoint representations of

Spectra of heterotic strings on orbifolds

SO(32)

Higgsino mass matrix ansatz for MSSM

, which are obtained by type I string and broken by compactification on orbifolds. Its single unified gauge coupling can give rise to different gauge couplings below the unification scale, due to effects of magnetic fluxes. The crucial mechanism is brane recombination preserving supersymmetry.

Z2 orbifold compactification of heterotic string and 6D SO(16) and E7×SU(2) flavor unification models

Abstract We obtain the spectrum of heterotic strings compactified on orbifolds, focusing on its algebraic structure. Affine Lie algebra provides its current algebra and representations. In particular, the twisted spectrum and the Abelian charge are understood. A twisted version of algebra is used in the homomorphism from the orbifold action to the group action. The relation between the conformal weight and the mass gives a useful rule.

Softening of the supersymmetry flavor problem from asymptotically free bulk interactions

Abstract An ansatz, Det M H =0, for the Higgsino mass matrix is suggested toward the minimal supersymmetric standard model (MSSM). Small instanton solutions effective around the GUT scale can fulfill this condition. An argument that the couplings contain a moduli field is given for a dynamical realization of this Higgsino mass matrix ansatz. We also present a string orbifold trinification toward this realization.

Gauge unification via stable brane recombination

Abstract A Z 2 orbifold compactification of the heterotic string is considered. The resulting 6D GUT groups can be SO (16) or E 7 × SU (2) plus some hidden sector groups. The N =4 supersymmetry is reduced to N =2. In particular, the SO (16) 6D model with one spinor representation 128 can reduce to the previous 5D SO (16) or SO (14) family unification models after compactifying the sixth dimension. To obtain one spinor, we have to take into account the left-over center of SO (16). We also comment on the E 7 × SU (2) model.

Dual description of the brane world cosmological constant with HMNPQ

Recently, it was pointed out that soft masses of the supersymmetric gauge theories with extra dimensions tend to a flavor conserving point, which is a desirable scenario in gravity mediation models. We point out that in 6D we must consider the anomaly-free condition in addition to the condition on asymptotic freedom. From this, we find that