37,282 research outputs found

### Properties of the top quark

Recent measurements of top-quark properties at the LHC and the Tevatron are
presented. Most recent measurements of the top quark mass have been carried out
by CMS using $19.7/$fb of $\sqrt{s} = 8$ TeV data including the study of the
dependence on event kinematics. ATLAS uses the full Run I data at $\sqrt{s} =
7$ TeV for a "3D" measurement that significantly reduces systematic
uncertainties. D0 employs the full Run II data using the matrix element method
to measure the top quark mass with significantly reduced systematic
uncertainties. Many different measurements of the top quark exist to date and
the most precise ones per decay channel per experiment have been combined into
the first world combination with a relative precision of 0.44%. Latest updates
of measurements of production asymmetries include the measurement of the \ttbar
production asymmetry by D0 employing the full Run II data set, by CMS and ATLAS
(including the polarization of the top quark) employing both the full data set
at $\sqrt{s} = 7$ TeV. CMS uses the full $\sqrt{s} = 8$ TeV data to measure the
top quark polarization in single top production, the ratio ${\cal R}$ of the
branching fractions ${\cal B}(t \rightarrow Wb) / {\cal B}(t \rightarrow Wq)$
and to search for flavor changing neutral currents. The results from all these
measurements agree well with their respective Standard Model expectation.Comment: Large Hadron Collider Physics (LHCP) conference held at Columbia
University in New York City from June 2-7, 201

### Lattice-coupled Antiferromagnet on Frustrated Lattices

Lattice-coupled antiferromagnetic spin model is analyzed for a number of
frustrated lattices: triangular, Kagome, and pyrochlore. In triangular and
Kagome lattices where ground state spins are locally ordered, the spin-lattice
interaction does not lead to a static deformation of the lattice. In the
pyrochlore structure, spin-lattice coupling supports a picture of the hexagon
spin cluster proposed in the recent experiment[S. H. Lee et al. Nature, 418,
856 (2002)]. Through spin-lattice interaction a uniform contraction of the
individual hexagons in the pyrochlore lattice can take place and reduce the
exchange energy. Residual hexagon-hexagon interaction takes the form of a
3-states Potts model where the preferred directions of the spin-loop directors
for nearby hexagons are mutually orthogonal

### Valence-bond-solid order in antiferromagnets with spin-lattice coupling

We propose that a valence-bond-solid (VBS) order can be stabilized in certain
two-dimensional antiferromagnets due to spin-lattice coupling. In contrast to
the VBS state of the Affleck-Kennedy-Lieb-Tesaki (AKLT) type in which the spin
$2S$ and the lattice coordination $z$ must be commensurate, the spin-lattice
coupling-induced VBS state can occur when $2S$ is not an integer multiple of
$z$. As a concrete example, S=2 spins on the triangular network with $z=6$ is
discussed. Within the Schwinger boson mean-field theory it is shown that the
ground state is given by the $\sqrt{3}\times\sqrt{3}$ modulation of the valence
bond amplitudes for sufficiently strong spin-lattice coupling. Using the
corresponding AKLT wave function, we work out the excitation spectrum for this
state within the single-mode approximation. The calculated spectrum should
provide a new type of collective mode which is distinct from the spin wave
excitations of the magnetically ordered ground state

### Transport in Almost Integrable Models: Perturbed Heisenberg Chains

The heat conductivity kappa(T) of integrable models, like the one-dimensional
spin-1/2 nearest-neighbor Heisenberg model, is infinite even at finite
temperatures as a consequence of the conservation laws associated with
integrability. Small perturbations lead to finite but large transport
coefficients which we calculate perturbatively using exact diagonalization and
moment expansions. We show that there are two different classes of
perturbations. While an interchain coupling of strength J_perp leads to
kappa(T) propto 1/J_perp^2 as expected from simple golden-rule arguments, we
obtain a much larger kappa(T) propto 1/J'^4 for a weak next-nearest neighbor
interaction J'. This can be explained by a new approximate conservation law of
the J-J' Heisenberg chain.Comment: 4 pages, several minor modifications, title change

### PROGRAM AND NONPROGRAM WHEAT ACREAGE RESPONSES TO PRICES AND RISK

Wheat acreage responses to expected wheat price and price risk are reversed for program and nonprogram-planted acreage in the northern plains, central plains, southern plains, and U.S. Expected wheat price has a strong negative effect on program-complying wheat acreage. Government support prices have a positive effect on program-complying and program-planted acreage. Price risk has a positive effect on program-complying wheat acreage and a negative effect on nonprogram-planted acreage. Estimated price elasticities are higher than in studies where risk was ignored.Demand and Price Analysis, Risk and Uncertainty,

### Comparison of techniques to reconstruct VHE gamma-ray showers from multiple stereoscopic Cherenkov images

For air showers observed simultaneously by more than two imaging atmospheric
Cherenkov telescopes, the shower geometry is overconstrained by the images and
image information should be combined taking into account the quality of the
images. Different algorithms are discussed and tested experimentally using data
obtained from observations of Mkn 501 with the HEGRA IACT system. Most of these
algorithms provide an estimate of the accuracy of the reconstruction of shower
geometry on an event-by-event basis, allowing, e.g., to select higher-quality
subsamples for precision measurements.Comment: 14 Pages, 6 figures, Late

### Does three-tangle properly quantify the three-party entanglement for Greenberger-Horne-Zeilinger-type states?

Some mixed states composed of only GHZ states can be expressed in terms of
only W-states. This fact implies that such states have vanishing three-tangle.
One of such rank-3 states, $\Pi_{GHZ}$, is explicitly presented in this paper.
These results are used to compute analytically the three-tangle of a rank-4
mixed state $\sigma$ composed of four GHZ states. This analysis with
considering Bloch sphere $S^{16}$ of $d=4$ qudit system allows us to derive the
hyper-polyhedron. It is shown that the states in this hyper-polyhedron have
vanishing three-tangle. Computing the one-tangles for $\Pi_{GHZ}$ and $\sigma$,
we prove the monogamy inequality explicitly. Making use of the fact that the
three-tangle of $\Pi_{GHZ}$ is zero, we try to explain why the W-class in the
whole mixed states is not of measure zero contrary to the case of pure states.Comment: 10 pages, no figure V2: new calculational results are included. 11
pages: V3 accepted in the Rapid Communication of PRA, 4 pages (two column

### Epitaxial growth and the magnetic properties of orthorhombic YTiO3 thin films

High-quality YTiO3 thin films were grown on LaAlO3 (110) substrates at low
oxygen pressures (<10-8 Torr) using pulsed laser deposition. The in-plane
asymmetric atomic arrangements at the substrate surface allowed us to grow
epitaxial YTiO3 thin films, which have an orthorhombic crystal structure with
quite different a- and b-axes lattice constants. The YTiO3 film exhibited a
clear ferromagnetic transition at 30 K with a saturation magnetization of about
0.7 uB/Ti. The magnetic easy axis was found to be along the [1-10] direction of
the substrate, which differs from the single crystal easy axis direction, i.e.,
[001].Comment: 14 pages, 4 figure

### The intrinsic strangeness and charm of the nucleon using improved staggered fermions

We calculate the intrinsic strangeness of the nucleon, - ,
using the MILC library of improved staggered gauge configurations using the
Asqtad and HISQ actions. Additionally, we present a preliminary calculation of
the intrinsic charm of the nucleon using the HISQ action with dynamical charm.
The calculation is done with a method which incorporates features of both
commonly-used methods, the direct evaluation of the three-point function and
the application of the Feynman- Hellman theorem. We present an improvement on
this method that further reduces the statistical error, and check the result
from this hybrid method against the other two methods and find that they are
consistent. The values for and found here, together with
perturbative results for heavy quarks, show that dark matter scattering through
Higgs-like exchange receives roughly equal contributions from all heavy quark
flavors.Comment: 17 pages, 14 figure

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