1,099 research outputs found
2 TeV Walking Technirho at LHC?
The ATLAS collaboration has recently reported an excess of about 2.5
global significance at around 2 TeV in the diboson channel with the
boson-tagged fat dijets, which may imply a new resonance beyond the standard
model. We provide a possible explanation of the excess as the isospin-triplet
technivector mesons (technirhos, denoted as ) of the walking
technicolor in the case of the one-family model as a benchmark. As the
effective theory for the walking technicolor at the scales relevant to the LHC
experiment, we take a scale-invariant version of the hidden local symmetry
model so constructed as to accommodate technipions, technivector mesons, and
the technidilaton in such a way that the model respects spontaneously broken
chiral and scale symmetries of the underlying walking technicolor. In
particular, the technidilaton, a (pseudo) Nambu-Goldstone boson of the
(approximate) scale symmetry predicted in the walking technicolor, has been
shown to be successfully identified with the 125 GeV Higgs. Currently available
LHC limits on those technihadrons are used to fix the couplings of technivector
mesons to the standard-model fermions and weak gauge bosons. We find that the
technirho's are mainly produced through the Drell-Yan process and predominantly
decay to the dibosons, which accounts for the currently reported excess at
around 2 TeV. The consistency with the electroweak precision test and other
possible discovery channels of the 2 TeV technirhos are also addressed.Comment: 8 pages, 4 eps figures, latex; version to appear in PL
Metal-insulator transition caused by the coupling to localized charge-frustrated systems under ice-rule local constraint
We report the results of our theoretical and numerical study on electronic
and transport properties of fermion systems with charge frustration. We
consider an extended Falicov-Kimball model in which itinerant spinless fermions
interact repulsively by U with localized particles whose distribution satisfies
a local constraint under geometrical frustration, the so-called ice rule. We
numerically calculate the density of states, optical conductivity, and inverse
participation ratio for the models on the pyrochlore, checkerboard, and kagome
lattices, and discuss the nature of metal-insulator transitions at commensurate
fillings. As a result, we show that the ice-rule local constraint leads to
several universal features in the electronic structure; a charge gap opens at a
considerably small U compared to the bandwidth, and the energy spectrum
approaches a characteristic form in the large U limit, that is, the
noninteracting tight-binding form in one dimension or the -functional
peak. In the large U region, the itinerant fermions are confined in the
macroscopically-degenerate ice-rule configurations, which consist of a bunch of
one-dimensional loops: We call this insulating state the charge ice. On the
other hand, transport properties are much affected by the geometry and
dimensionality of lattices; e.g., the pyrochlore lattice model exhibits a
transition from a metallic to the charge-ice insulating state by increasing U,
while the checkerboard lattice model appears to show Anderson localization
before opening a gap. Meanwhile, in the kagome lattice case, we do not obtain
clear evidence of Anderson localization. Our results elucidate the universality
and diversity of phase transitions to the charge-ice insulator in fully
frustrated lattices.Comment: 16 pages, 17 figure
Quantum melting of charge ice and non-Fermi-liquid behavior: An exact solution for the extended Falicov-Kimball model in the ice-rule limit
An exact solution is obtained for a model of itinerant electrons coupled to
ice-rule variables on the tetrahedron Husimi cactus, an analogue of the Bethe
lattice of corner-sharing tetrahedra. It reveals a quantum critical point with
the emergence of non-Fermi-liquid behavior in melting of the "charge ice"
insulator. The electronic structure is compared with the numerical results for
the pyrochlore-lattice model to elucidate the physics of electron systems
interacting with the tetrahedron ice rule.Comment: 5 pages, 4 figure
Baryons with D5 Brane Vertex and k-Quarks
We study baryons in SU(N) gauge theories, according to the gauge/string
correspondence based on IIB string theory. The D5 brane, in which
fundamental strings are dissolved as a color singlet, is introduced as the
baryon vertex, and its configurations are studied. We find point- and
split-type of vertex. In the latter case, two cusps appears and they are
connected by a flux composed of dissolved fundamental strings with a definite
tension. In both cases, fundamental quarks are attached on the cusp(s) of
the vertex to cancel the surface term. In the confining phase, we find that the
quark in the baryon feel the potential increasing linearly with the distance
from the vertex. At finite temperature and in the deconfining phase, we find a
stable k-quarks "baryons", which are constructed of arbitrary number of
quarks.Comment: 20 pages, 11 figure
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Advances in Kriging-Based Autonomous X-Ray Scattering Experiments.
Autonomous experimentation is an emerging paradigm for scientific discovery, wherein measurement instruments are augmented with decision-making algorithms, allowing them to autonomously explore parameter spaces of interest. We have recently demonstrated a generalized approach to autonomous experimental control, based on generating a surrogate model to interpolate experimental data, and a corresponding uncertainty model, which are computed using a Gaussian process regression known as ordinary Kriging (OK). We demonstrated the successful application of this method to exploring materials science problems using x-ray scattering measurements at a synchrotron beamline. Here, we report several improvements to this methodology that overcome limitations of traditional Kriging methods. The variogram underlying OK is global and thus insensitive to local data variation. We augment the Kriging variance with model-based measures, for instance providing local sensitivity by including the gradient of the surrogate model. As with most statistical regression methods, OK minimizes the number of measurements required to achieve a particular model quality. However, in practice this may not be the most stringent experimental constraint; e.g. the goal may instead be to minimize experiment duration or material usage. We define an adaptive cost function, allowing the autonomous method to balance information gain against measured experimental cost. We provide synthetic and experimental demonstrations, validating that this improved algorithm yields more efficient autonomous data collection
Cluster dynamical mean-field study of the Hubbard model on a 3D frustrated hyperkagome lattice
We study the Hubbard model on a geometrically-frustrated hyperkagome lattice
by a cluster extension of the dynamical mean field theory. We calculate the
temperature () dependences of the specific heat () and the spin-lattice
relaxation time () in correlated metallic region. shows a peak at
and rapidly decreases as . On the other hand, has a
peak at a higher temperature than , and largely decreases
below , followed by the Korringa law as . Both
peak temperatures are suppressed and the peaks become sharper as electron
correlation is increased. These behaviors originate from strong renormalization
of the energy scales in the peculiar electronic structure in this frustrated
system; a pseudo-gap like feature, the van-Hove singularity, and the flat band.
The results are discussed in comparison with the experimental data in the
hyperkagome material, NaIrO.Comment: 4 pages, 4 figures, Conference proceedings for Highly Frustrated
Magnetism 200
Relativistic viscoelastic fluid mechanics
A detailed study is carried out for the relativistic theory of
viscoelasticity which was recently constructed on the basis of Onsager's linear
nonequilibrium thermodynamics. After rederiving the theory using a local
argument with the entropy current, we show that this theory universally reduces
to the standard relativistic Navier-Stokes fluid mechanics in the long time
limit. Since effects of elasticity are taken into account, the dynamics at
short time scales is modified from that given by the Navier-Stokes equations,
so that acausal problems intrinsic to relativistic Navier-Stokes fluids are
significantly remedied. We in particular show that the wave equations for the
propagation of disturbance around a hydrostatic equilibrium in Minkowski
spacetime become symmetric hyperbolic for some range of parameters, so that the
model is free of acausality problems. This observation suggests that the
relativistic viscoelastic model with such parameters can be regarded as a
causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting
parameters to various values, this theory can treat a wide variety of materials
including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a
nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus
we expect the theory to be the most universal description of single-component
relativistic continuum materials. We also show that the presence of strains and
the corresponding change in temperature are naturally unified through the
Tolman law in a generally covariant description of continuum mechanics.Comment: 52pages, 11figures; v2: minor corrections; v3: minor corrections, to
appear in Physical Review E; v4: minor change
Identifying Better Effective Higgsless Theories via W_L W_L Scattering
The three site Higgsless model has been offered as a benchmark for studying
the collider phenomenology of Higgsless models. In this talk, we present how
well the three site Higgsless model performs as a general representative of
Higgsless models in describing W_L W_L scattering, and which modifications can
make it more representative. We employ general sum rules relating the masses
and couplings of the Kaluza-Klein (KK) modes of the gauge fields in continuum
and deconstructed Higgsless models as a way to compare the different theories.
After comparing the three site Higgsless model to flat and warped continuum
Higgsless models, we analyze an extensions of the three site Higgsless model,
namely, the Hidden Local Symmetry (HLS) Higgsless model. We demonstrate that
W_LW_L scattering in the HLS Higgsless model can very closely approximate
scattering in the continuum models, provided that the parameter `a' is chosen
to mimic rho-meson dominance of pi-pi scattering in QCD
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