In-Gyu Koh

The Strong CP Problem and Axion Invisibility

Abstract We introduce a new concept of automatic symmetry in order to set the guidelines for the Higgs content and couplings in grand unified theories. We then demonstrate that the global U(1) symmetries in the standard model and in the SU(5) model cannot satisfy the color anomaly condition and the automaticity condition simultaneously. We finally give the results for three types of SU(7) model in which a global U(1) symmetry arises automatically . Various situations are observed depending on the symmetry breaking patterns and charge assignments.

Quantum dimensions and modular forms in chiral conformal theory

Abstract Extended chiral field theories with an internal quantum symmetry are characterized by a modular formM(τ) covariant under a subgroup ΓN0ofΓ =SL(2,Z). This subgroup is known to be the modular group of a theory with twisted boundary To each modular invariant partition functionZ of the ADE classification of corresponds a formM but some of theMs are images of two differentZs.

Mass spectra in SU(5) supersymmetric models of grand unification with Higgs particles in representations 75 or 24

Abstract The results of a computation of mass spectra in SUSY models of grand unification in SU(5) are presented. The method uses systematically weight vectors as bases for representation spaces. It is briefly explained on an SU(3) model which, in this formalism, has all technical features occuring in higher groups. General criteria for the choice of Higgs representation are pointed out.

Locally supersymmetric grand unified theory with two-loop stable mass hierarchy☆

Abstract The local supersymmetric grand unified theory with 75, 50, 50∗, 5, 5∗ and two singlets is shown to have two-loop stable mass hierarchy in addition to the one-loop stability. The right local SUSY GUT can be selected out between this model and other SU(5) models by the measurement of the gluino mass, which is sensitive to heavy Higgs contents.

Grand unified models with several generations and without domain walls

Abstract The cosmological requirement of no domain wall gives a rather severe constraint to the number of fermion generations. We report on the results of our extensive search for grand unified models that can accomodate three or more generations of fermions and yet without suffering from the potentially catastrophic domain walls.

The low mass monopole and the invisible axion in grand unified theories

Abstract We construct an SU(7) grand unification model that contains both low-mass monopoles and an invisible axion. The method described here can easily be incorporated in any grand unified theory.