12,783 research outputs found

    Global yield curve dynamics and interactions: a dynamic Nelson-Siegel approach

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    The popular Nelson-Siegel (1987) yield curve is routinely fit to cross sections of intra-country bond yields, and Diebold and Li (2006) have recently proposed a dynamized version. In this paper we extend Diebold-Li to a global context, modeling a potentially large set of country yield curves in a framework that allows for both global and country-specific factors. In an empirical analysis of term structures of government bond yields for the Germany, Japan, the U.K. and the U.S., we find that global yield factors do indeed exist and are economically important, generally explaining significant fractions of country yield curve dynamics, with interesting differences across countries

    PSR B1828-11: a precession pulsar torqued by a quark planet?

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    The pulsar PSR B1828-11 has long-term, highly periodic and correlated variations in both pulse shape and the rate of slow-down. This phenomenon may provide evidence for precession of the pulsar as suggested previously within the framework of free precession as well as forced one. On a presumption of forced precession, we propose a quark planet model to this precession henomenon instead, in which the pulsar is torqued by a quark planet. We construct this model by constraining mass of the pulsar (MpsrM_{\rm psr}), mass of the planet (MplM_{\rm pl}) and orbital radius of the planet (rplr_{\rm pl}). Five aspects are considered: derived relation between MpsrM_{\rm psr} and rplr_{\rm pl}, movement of the pulsar around the center of mass, ratio of MpsrM_{\rm psr} and MplM_{\rm pl}, gravitational wave radiation timescale of the planetary system, and death-line criterion. We also calculate the range of precession period derivative and gravitational wave strength (at earth) permitted by the model. Under reasonable parameters, the observed phenomenon can be understood by a pulsar (104101M10^{-4}\sim10^{-1}M_{\odot}) with a quark planet (108103M10^{-8}\sim10^{-3}M_{\odot}) orbiting it. According to the calculations presented, the pulsar would be a quark star because of its low mass, which might eject a lump of quark matter (to become a planet around) during its birth.Comment: 6 pages, 3 figures, accepted by MNRAS (Letters

    Global Yield Curve Dynamics and Interactions: A Dynamic Nelson-Siegel Approach

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    The popular Nelson-Siegel (1987) yield curve is routinely fit to cross sections of intra-country bond yields, and Diebold and Li (2006) have recently proposed a dynamized version. In this paper we extend Diebold-Li to a global context, modeling a potentially large set of country yield curves in a framework that allows for both global and country-specific factors. In an empirical analysis of term structures of government bond yields for the Germany, Japan, the U.K. and the U.S., we find that global yield factors do indeed exist and are economically important, generally explaining significant fractions of country yield curve dynamics, with interesting differences across countries.Term Structure, Interest Rate, Dynamic Factor Model, Global Yield, World Yield, Bond Market

    Effects of unparticle on top spin correlation at the Large Hadron Collider

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    We study effects of the scale invariant hidden sector, unparticle, proposed by Georgi, on top spin correlation at the Large Hadron Collider. Assuming no flavor changing interaction between the unparticles and the Standard Model particles, there arises the top-antitop quark pair production process through virtual unparticle exchanges in the s-channel in addition to the Standard Model processes. In particular, we consider contributions of scalar and vector unparticles and find that these make sizable deviations of the top spin correlation from the Standard Model one.Comment: 29 pages, 1 table, 12 figures, 2 figures added, typos in captions corrected, version accepted for publication in PR

    Spin superconductor in ferromagnetic graphene

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    We show a spin superconductor (SSC) in ferromagnetic graphene as the counterpart to the charge superconductor, in which a spin-polarized electron-hole pair plays the role of the spin 2(/2)2 (\hbar/2) `Cooper pair' with a neutral charge. We present a BCS-type theory for the SSC. With the `London-type equations' of the super-spin-current density, we show the existence of an electric `Meissner effect' against a spatial varying electric field. We further study a SSC/normal conductor/SSC junction and predict a spin-current Josephson effect.Comment: 6 pages, 4 figure

    Abelian and non-abelian anyons in integer quantum anomalous Hall effect and topological phase transitions via superconducting proximity effect

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    We study the quantum anomalous Hall effect described by a class of two-component Haldane models on square lattices. We show that the latter can be transformed into a pseudospin triplet p+ip-wave paired superfluid. In the long wave length limit, the ground state wave function is described by Halperin's (1,1,-1) state of neutral fermions analogous to the double layer quantum Hall effect. The vortex excitations are charge e/2 abelian anyons which carry a neutral Dirac fermion zero mode. The superconducting proximity effect induces `tunneling' between `layers' which leads to topological phase transitions whereby the Dirac fermion zero mode fractionalizes and Majorana fermions emerge in the edge states. The charge e/2 vortex excitation carrying a Majorana zero mode is a non-abelian anyon. The proximity effect can also drive a conventional insulator into a quantum anomalous Hall effect state with a Majorana edge mode and the non-abelian vortex excitations.Comment: 6 pages, 4 figures, accepted by Phys. Rev.

    Numerical modeling study of the momentum deposition of small amplitude gravity waves in the thermosphere

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    We study the momentum deposition in the thermosphere from the dissipation of small amplitude gravity waves (GWs) within a wave packet using a fully nonlinear two-dimensional compressible numerical model. The model solves the nonlinear propagation and dissipation of a GW packet from the stratosphere into the thermosphere with realistic molecular viscosity and thermal diffusivity for various Prandtl numbers. The numerical simulations are performed for GW packets with initial vertical wavelengths (&lambda;<sub><i>z</i></sub>) ranging from 5 to 50 km. We show that &lambda;<sub><i>z</i></sub> decreases in time as a GW packet dissipates in the thermosphere, in agreement with the ray trace results of Vadas and Fritts (2005) (VF05). We also find good agreement for the peak height of the momentum flux (<i>z</i><sub>diss</sub>) between our simulations and VF05 for GWs with initial &lambda;<sub><i>z</i></sub> &le; 2&pi; <i>H</i> in an isothermal, windless background, where <i>H</i> is the density scale height. We also confirm that <i>z</i><sub>diss</sub> increases with increasing Prandtl number. We include eddy diffusion in the model, and find that the momentum deposition occurs at lower altitudes and has two separate peaks for GW packets with small initial &lambda;<sub><i>z</i></sub>. We also simulate GW packets in a non-isothermal atmosphere. The net &lambda;<sub><i>z</i></sub> profile is a competition between its decrease from viscosity and its increase from the increasing background temperature. We find that the wave packet disperses more in the non-isothermal atmosphere, and causes changes to the momentum flux and &lambda;<sub><i>z</i></sub> spectra at both early and late times for GW packets with initial &lambda;<sub><i>z</i></sub> &ge; 10 km. These effects are caused by the increase in <i>T</i> in the thermosphere, and the decrease in <i>T</i> near the mesopause
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