13,256 research outputs found
Global yield curve dynamics and interactions: a dynamic Nelson-Siegel approach
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?
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 (), mass of the planet
() and orbital radius of the planet (). Five aspects
are considered: derived relation between and ,
movement of the pulsar around the center of mass, ratio of and
, 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 () with a quark planet
() 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
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
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
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 `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
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
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 (λ<sub><i>z</i></sub>)
ranging from 5 to 50 km. We show that λ<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 λ<sub><i>z</i></sub> ≤ 2π <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 λ<sub><i>z</i></sub>. We also simulate GW packets in a
non-isothermal atmosphere. The net λ<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
λ<sub><i>z</i></sub> spectra at both early and late times for GW packets with
initial λ<sub><i>z</i></sub> ≥ 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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