32,679 research outputs found
Einstein Manifolds As Yang-Mills Instantons
It is well-known that Einstein gravity can be formulated as a gauge theory of
Lorentz group where spin connections play a role of gauge fields and Riemann
curvature tensors correspond to their field strengths. One can then pose an
interesting question: What is the Einstein equations from the gauge theory
point of view? Or equivalently, what is the gauge theory object corresponding
to Einstein manifolds? We show that the Einstein equations in four dimensions
are precisely self-duality equations in Yang-Mills gauge theory and so Einstein
manifolds correspond to Yang-Mills instantons in SO(4) = SU(2)_L x SU(2)_R
gauge theory. Specifically, we prove that any Einstein manifold with or without
a cosmological constant always arises as the sum of SU(2)_L instantons and
SU(2)_R anti-instantons. This result explains why an Einstein manifold must be
stable because two kinds of instantons belong to different gauge groups,
instantons in SU(2)_L and anti-instantons in SU(2)_R, and so they cannot decay
into a vacuum. We further illuminate the stability of Einstein manifolds by
showing that they carry nontrivial topological invariants.Comment: v4; 17 pages, published version in Mod. Phys. Lett.
Higgs bosons of a supersymmetric model at the Large Hadron Collider
It is found that CP symmetry may be explicitly broken in the Higgs sector of
a supersymmetric model with two extra neutral gauge bosons at the
one-loop level. The phenomenology of the model, the Higgs sector in particular,
is studied for a reasonable parameter space of the model, in the presence of
explicit CP violation at the one-loop level. At least one of the neutral Higgs
bosons of the model might be produced via the fusion process at the Large
Hadron Collider.Comment: 23 pages, 5 figures, JHE
Explicit CP violation in a MSSM with an extra
We study that a minimal supersymmetric standard model with an extra
gauge symmetry may accommodate the explicit CP violation at the one-loop level
through radiative corrections. This model is CP conserving at the tree level
and cannot realize the spontaneous CP violation for a wide parameter space at
the one-loop level. In explicit CP violation scenario, we calculate the Higgs
boson masses and the magnitude of the scalar-pseudoscalar mixings in this model
at the one-loop level by taking into account the contributions of top quarks,
bottom quarks, exotic quarks, and their superpartners. In particular, we
investigate how the exotic quarks and squarks would affect the
scalar-pseudoscalar mixings. It is observed that the size of the mixing between
the heaviest scalar and pseudoscalar Higgs bosons is changed up to 20 % by a
complex phase originated from the exotic quark sector of this model.Comment: 19 pages, 3 figure
Photoproduction of Xi off nucleons
The photoproduction reaction is investigated based on
a relativistic meson-exchange model of hadronic interactions. The production
amplitude is calculated in the tree-level approximation from relevant effective
Lagrangians, whose (coupling constant) parameters are mostly fixed from the
empirical data and/or quark models together with SU(3) symmetry considerations.
Gauge invariance of the resulting amplitude is maintained by introducing the
contact currents by extending the gauge-invariant approach of Haberzettl for
one-meson photoproduction to two-meson photoproduction. The role of the
intermediate low-lying hyperons and of the intermediate higher-mass hyperon
resonances are analyzed in detail. In particular, the basic features of the
production of in and their possible
manifestations in the forthcoming experimental data are discussed.Comment: 18 pages, 17 figures, REVTeX, 1 figure added, to appear in Phys. Rev.
Higgs bosons of a supersymmetric model at the ILC
We study the scalar Higgs sector of the next-to-minimal supersymmetric
standard model with an extra U(1), which has two Higgs doublets and a Higgs
singlet, in the light leptophobic scenario where the extra neutral gauge
boson does not couple to charged leptons. In this model, we find that the
sum of the squared coupling coefficients of the three neutral scalar Higgs
bosons to , normalized by the corresponding SM coupling coefficient is
noticeably smaller than unity, due to the effect of the extra U(1), for a
reasonable parameter space of the model, whereas it is unity in the
next-to-minimal supersymmetric standard model. Thus, these two models may be
distinguished if the coupling coefficients of neutral scalar Higgs bosons to
are measured at the future International Linear Collider by producing them
via the Higgs-strahlung, fusion, and fusion processes.Comment: 12 pages, 2 figures, 1 table, PR
Charmonium-hadron interactions from QCD
The heavy quark system is an excellent probe to learn about the QCD dynamics
at finite density. First, we discuss the properties of the and
meson at finite nucleon density. We discuss why their properties should change
at finite density and then introduce an exact QCD relation among these hadron
properties and the energy momentum tensor of the medium. Second, we discuss
attempts to calculate charmonium-hadron total cross section using effective
hadronic models and perturbative QCD. We emphasize a recent calculation, where
the cross section is derived using QCD factorization theorem. We conclude by
discussing some challenges for SIS 200.Comment: 8 pages, Presented at 6th International Conference on Strange Quarks
in Matter: 2001: A Flavorspace Odyssey (SQM2001), Frankfurt, Germany, 25-29
Sep 2001, submitted to J. Phys.
Exotic quark effects on the Higgs sector of the USSM at the LHC
The Higgs sector of the U(1)-extended supersymmetric model is studied with
great detail. We calculate the masses of the Higgs bosons at the one-loop
level. We also calculate at the one-loop level the gluon-involving processes
for the productions and decays of the scalar Higgs bosons of the model at the
energy of the CERN Large Hadron Collider (LHC), where the radiative corrections
due to the loops of top, bottom, and exotic quarks and their scalar partners
are taken into account. We find that the exotic quark and exotic scalar quarks
in the model may manifest themselves at the LHC, since the production of the
heaviest scalar Higgs boson via gluon fusion processes is mediated virtually by
the loops of exotic quark and exotic scalar quarks, for a reasonable parameter
set of the model.Comment: 36 pages, 13 figures, JP
Application of Artificial Neural Network to Search for Gravitational-Wave Signals Associated with Short Gamma-Ray Bursts
We apply a machine learning algorithm, the artificial neural network, to the
search for gravitational-wave signals associated with short gamma-ray bursts.
The multi-dimensional samples consisting of data corresponding to the
statistical and physical quantities from the coherent search pipeline are fed
into the artificial neural network to distinguish simulated gravitational-wave
signals from background noise artifacts. Our result shows that the data
classification efficiency at a fixed false alarm probability is improved by the
artificial neural network in comparison to the conventional detection
statistic. Therefore, this algorithm increases the distance at which a
gravitational-wave signal could be observed in coincidence with a gamma-ray
burst. In order to demonstrate the performance, we also evaluate a few seconds
of gravitational-wave data segment using the trained networks and obtain the
false alarm probability. We suggest that the artificial neural network can be a
complementary method to the conventional detection statistic for identifying
gravitational-wave signals related to the short gamma-ray bursts.Comment: 30 pages, 10 figure
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