516 research outputs found
Higher-Dimensional QCD without the Strong CP Problem
QCD in a five-dimensional sliced bulk with chiral extra-quarks on the
boundaries is generically free from the strong CP problem. Accidental axial
symmetry is naturally present except for suppressed breaking interactions,
which plays a role of the Peccei-Quinn symmetry to make the strong CP phase
sufficiently small.Comment: 7 pages, late
Super- and CP-symmetric QCD in Higher Dimensions
An extremely precise global symmetry is necessary in the Peccei--Quinn
solution to the strong CP problem. Such symmetry arises when colored chiral
fermions are localized in an internal space. We present a supersymmetric model
that incorporates the above mechanism. Extra colored chiral multiplets around
the supersymmetry-breaking scale are a generic prediction of the supersymetric
model.Comment: 10 page
Product-Group Unification in Type IIB String Thoery
The product-group unification is a model of unified theories, in which
masslessness of the two Higgs doublets and absence of dimension-five proton
decay are guaranteed by a symmetry. It is based on SU(5) x U(N) (N=2,3) gauge
group. It is known that various features of the model are explained naturally,
when it is embedded in a brane world. This article describes an idea of how to
accommodate all the particles of the model in Type IIB brane world. The
GUT-breaking sector is realized by a D3--D7 system, and chiral quarks and
leptons arise from intersection of D7-branes. The D-brane configuration can be
a geometric realization of the non-parallel family structure of quarks and
leptons, an idea proposed to explain the large mixing angles observed in the
neutrino oscillation. The tri-linear interaction of the next-to-minimal
supersymmetric standard model is obtained naturally in some cases.Comment: 33 pages, 5 figure
Model Building with Gauge-Yukawa Unification
In supersymmetric theories with extra dimensions, the Higgs and matter fields
can be part of the gauge multiplet, so that the Yukawa interactions can arise
from the gauge interactions. This leads to the possibility of gauge-Yukawa
coupling unification, g_i=y_f, in the effective four dimensional theory after
the initial gauge symmetry and the supersymmetry are broken upon orbifold
compactification. We consider gauge-Yukawa unified models based on a variety of
four dimensional symmetries, including SO(10), SU(5), Pati-Salam symmetry,
trinification, and the Standard Model. Only in the case of Pati-Salam and the
Standard Model symmetry, we do obtain gauge-Yukawa unification. Partial
gauge-Yukawa unification is also briefly discussed.Comment: 23 page
Analysis of strain and stacking faults in single nanowires using Bragg coherent diffraction imaging
Coherent diffraction imaging (CDI) on Bragg reflections is a promising
technique for the study of three-dimensional (3D) composition and strain fields
in nanostructures, which can be recovered directly from the coherent
diffraction data recorded on single objects. In this article we report results
obtained for single homogeneous and heterogeneous nanowires with a diameter
smaller than 100 nm, for which we used CDI to retrieve information about
deformation and faults existing in these wires. The article also discusses the
influence of stacking faults, which can create artefacts during the
reconstruction of the nanowire shape and deformation.Comment: 18 pages, 6 figures Submitted to New Journal of Physic
Structure and Magnetism of Neutral and Anionic Palladium Clusters
The properties of neutral and anionic Pd_N clusters were investigated with
spin-density-functional calculations. The ground state structures are
three-dimensional for N>3 and they are magnetic with a spin-triplet for 2<=N<=7
and a spin nonet for N=13 neutral clusters. Structural- and spin-isomers were
determined and an anomalous increase of the magnetic moment with temperature is
predicted for a Pd_7 ensemble. Vertical electron detachment and ionization
energies were calculated and the former agree well with measured values for
anionic Pd_N clusters.Comment: 5 pages, 3 figures, fig. 2 in color, accepted to Phys. Rev. Lett.
(2001
Semi-simple group unification in the supersymmetric brane world
The conventional supersymmetric grand unified theories suffer from two
serious problems, the large mass splitting between doublet and triplet Higgs
multiplets, and the too long lifetime of the proton. A unification model based
on a semi-simple group SU(5)_{GUT} \times U(3)_H has been proposed to solve
both of the problems simultaneously. Although the proposed model is perfectly
consistent with observations, there are various mysteries. In this paper, we
show that such mysterious features in the original model are naturally
explained by embedding the model into the brane world in a higher dimensional
space-time. In particular, the relatively small gauge coupling constant of the
SU(5)_{GUT} at the unification energy scale is a consequence of relatively
large volume of extra dimensions. Here, we put the SU(5)_{GUT} gauge multiplet
in a 6-dimensional bulk and assume all fields in the U(3)_H sector to reside on
a 3-dimensional brane located in the bulk. On the other hand, all chiral
multiplets of quarks, leptons and Higgs are assumed to reside on a 3-brane at a
T^2/Z_4 orbifold fixed point. The quasi-N=2 supersymmetry in the hypercolor
U(3)_H sector is understood as a low-energy remnant of the N=4 supersymmetry in
a 6-dimensional space-time. We further extend the 6-dimensional model to a
10-dimensional theory. Possible frameworks of string theories are also
investigated to accommodate the present brane-world model. We find that the
type IIB string theory with D3-D7 brane structure is an interesting candidate.Comment: 45 pages, including 1 figure, minor correctio
Comprehensive characterization of molecular interactions based on nanomechanics
Molecular interaction is a key concept in our understanding of the biological mechanisms of life. Two physical properties change when one molecular partner binds to another. Firstly, the masses combine and secondly, the structure of at least one binding partner is altered, mechanically transducing the binding into subsequent biological reactions. Here we present a nanomechanical micro-array technique for bio-medical research, which not only monitors the binding of effector molecules to their target but also the subsequent effect on a biological system in vitro. This label-free and real-time method directly and simultaneously tracks mass and nanomechanical changes at the sensor interface using micro-cantilever technology. To prove the concept we measured lipid vesicle (approximately 748*10(6) Da) adsorption on the sensor interface followed by subsequent binding of the bee venom peptide melittin (2840 Da) to the vesicles. The results show the high dynamic range of the instrument and that measuring the mass and structural changes simultaneously allow a comprehensive discussion of molecular interactions
Inflationary Cosmology with Five Dimensional SO(10)
We discuss inflationary cosmology in a five dimensional SO(10) model
compactified on , which yields below the compactification scale. The gauge
symmetry is preserved on one of the fixed points, while
``flipped'' is on the other fixed point. Inflation is
associated with breaking, and is implemented through -term scalar
potentials on the two fixed points. A brane-localized Einstein-Hilbert term
allows both branes to have positive tensions during inflation. The scale of
breaking is fixed from measurements to be around
GeV, and the scalar spectral index . The inflaton field
decays into right-handed neutrinos whose subsequent out of equilibrium decay
yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in
PR
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