14,694 research outputs found

### 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

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