Horizontal symmetry in Higgs sector of GUT with U(1)_A symmetry

In a series of papers, we pointed out that an anomalous $U(1)_A$ gauge symmetry naturally solves various problems in grand unified theories (GUTs) and that a horizontal gauge symmetry, $SU(2)_H$ or $SU(3)_H$, not only realizes the unification of three generation quarks and leptons in fewer multiplets but also solves the supersymmetric flavor problem. In this paper, we examine the possibility that the Higgs sectors of the GUT symmetry and of the horizontal symmetry are unified, that is, there are some Higgs fields whose vacuum expectation values (VEVs) break both the GUT gauge symmetry and the horizontal symmetry at the same time. Although the scale of the VEVs become too large to suppress the flavor changing neutral current processes sufficiently, the unification is possible. In addition, for the $SU(3)_H$ models, the $SU(3)_H$ gauge anomaly is cancelled in the unified models without introducing additional fields in contrast with the previous models in which the Higgs sectors are not unified.Comment: 35 page

Gauge Coupling Unification with Anomalous U(1)_A Gauge Symmetry

Recently we proposed a natural scenario of grand unified theories with anomalous U(1)_A gauge symmetry, in which doublet-triplet splitting is realized in SO(10) unification using Dimopoulos-Wilczek mechanism and realistic quark and lepton mass matrices can be obtained in a simple way. The scenario has an additional remarkable feature that the symmetry breaking scale and the mass spectrum of super heavy particles are determined essentially by anomalous U(1)_A charges. Therefore once all the anomalous U(1)_A charges are fixed, the gauge coupling flows can be calculated. We examine several models in which the gauge coupling unification is realized. Examining the conditions for the coupling unification, we show that when all the fields except those of the minimal SUSY standard model become super-heavy, the unification scale generically becomes just below the usual GUT scale \Lambda_G\sim 2\times 10^{16} GeV and the cutoff scale becomes around \Lambda_G. Since the lower GUT scale leads to shorter life time of nucleon, the proton decay via dimension six operator p\to e^+\pi^0 can be seen in future experiment. On the other hand, the lower cutoff scale than the Planck scale may imply the existence of extra dimension in which only gravity modes can propagate.Comment: LATeX 26 pages, 1 figure, V3:the economical condition and typos are correcte

Duality of a Supersymmetric Standard Model

We examine a dual theory of a Supersymmetric Standard Model(SSM) in terms of an $SU(3)_C$ gauge group. In this scenario, it is naturally understood that at least one quark (the top quark) should be heavy, i.e., almost the same order as the weak scale. Moreover, the supersymmetric Higgs mass parameter $\mu$ can naturally be expected to be small. This model automatically induces nine pairs of composite Higgs fields, which may be observed in the near future.Comment: 9 pages, LaTe

Neutrino masses, anomalous U(1) gauge symmetry and doublet-triplet splitting

We propose an attractive scenario of grand unified theories in which doublet-triplet splitting is beautifully realized in SO(10) unification using Dimopoulos-Wilczek mechanism. The anomalous U(1)_A gauge symmetry plays essential roles in the doublet-triplet splitting mechanism. It is interesting that the anomalous U(1)_A charges determine the unification scale and mass spectrum of additional particles as well as the order of Yukawa couplings of quarks and leptons. For the neutrino sector, bi-maximal mixing angles are naturally obtained and proton decay via dimension 5 operators is suppressed. It is suggestive that the anomalous U(1)_A gauge symmetry motivated by superstring theory excellently solves the two biggest problems in grand unified theories, fermion mass hierarchy problem and doublet-triplet splitting problem.Comment: 20 pages, typos are corrected, refs are adde

Vector-like Strong Coupling theory with small S and T parameters

We propose a mechanism which can reduce the Peskin and Takeuchi's S, T and U parameters in dynamical electroweak symmetry breaking models. It is interesting that not only S but also T parameter can become small even if there exists large isospin violation in fermion condensation. For example, when we take the $SU(2)_L\times U(1)_Y$ breaking mass of up-type fermion $m_U=1$ TeV and that of down-type $m_D=0$, we get S$\sim 0.001 N$ and T$\sim 0.05 N$ for the $SU(2)_L\times U(1)_Y$ invariant masses $M=10$ TeV. The point is that these parameters are suppressed by $SU(2)_L\times U(1)_Y$ invariant masses which the vector-like fermions can have