37,282 research outputs found

    Properties of the top quark

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    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 19.7/19.7/fb of s=8\sqrt{s} = 8 TeV data including the study of the dependence on event kinematics. ATLAS uses the full Run I data at s=7\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 s=7\sqrt{s} = 7 TeV. CMS uses the full s=8\sqrt{s} = 8 TeV data to measure the top quark polarization in single top production, the ratio R{\cal R} of the branching fractions B(tWb)/B(tWq){\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

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    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

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    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 2S2S and the lattice coordination zz must be commensurate, the spin-lattice coupling-induced VBS state can occur when 2S2S is not an integer multiple of zz. As a concrete example, S=2 spins on the triangular network with z=6z=6 is discussed. Within the Schwinger boson mean-field theory it is shown that the ground state is given by the 3×3\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

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    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

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    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

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    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?

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    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, ΠGHZ\Pi_{GHZ}, is explicitly presented in this paper. These results are used to compute analytically the three-tangle of a rank-4 mixed state σ\sigma composed of four GHZ states. This analysis with considering Bloch sphere S16S^{16} of d=4d=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 ΠGHZ\Pi_{GHZ} and σ\sigma, we prove the monogamy inequality explicitly. Making use of the fact that the three-tangle of ΠGHZ\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

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    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

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    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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