1,657 research outputs found
Studies of the limit order book around large price changes
We study the dynamics of the limit order book of liquid stocks after
experiencing large intra-day price changes. In the data we find large
variations in several microscopical measures, e.g., the volatility the bid-ask
spread, the bid-ask imbalance, the number of queuing limit orders, the activity
(number and volume) of limit orders placed and canceled, etc. The relaxation of
the quantities is generally very slow that can be described by a power law of
exponent . We introduce a numerical model in order to understand
the empirical results better. We find that with a zero intelligence deposition
model of the order flow the empirical results can be reproduced qualitatively.
This suggests that the slow relaxations might not be results of agents'
strategic behaviour. Studying the difference between the exponents found
empirically and numerically helps us to better identify the role of strategic
behaviour in the phenomena.Comment: 19 pages, 7 figure
Vector Meson Mixing and Charge Symmetry Violation
We discuss the consistency of the traditional vector meson dominance (VMD)
model for photons coupling to matter, with the vanishing of vector meson-meson
and meson-photon mixing self-energies at q^2=0. This vanishing of vector mixing
has been demonstrated in the context of rho-omega mixing for a large class of
effective theories. As a further constraint on such models, we here apply them
to a study of photon-meson mixing and VMD. As an example we compare the
predicted momentum dependence of one such model with a momentum-dependent
version of VMD discussed by Sakurai in the 1960's. We find that it produces a
result which is consistent with the traditional VMD phenomenology. We conclude
that comparison with VMD phenomenology can provide a useful constraint on such
models.Comment: 7 pages, uses epsfig.sty. Publication details added to title pag
Anatomy of Spin-Transfer Torque
Spin-transfer torques occur in magnetic heterostructures because the
transverse component of a spin current that flows from a non-magnet into a
ferromagnet is absorbed at the interface. We demonstrate this fact explicitly
using free electron models and first principles electronic structure
calculations for real material interfaces. Three distinct processes contribute
to the absorption: (1) spin-dependent reflection and transmission; (2) rotation
of reflected and transmitted spins; and (3) spatial precession of spins in the
ferromagnet. When summed over all Fermi surface electrons, these processes
reduce the transverse component of the transmitted and reflected spin currents
to nearly zero for most systems of interest. Therefore, to a good
approximation, the torque on the magnetization is proportional to the
transverse piece of the incoming spin current.Comment: 16 pages, 8 figures, submitted to Phys. Rev.
Gaussian Tunneling Model of c-Axis Twist Josephson Junctions
We calculate the critical current density for c-axis Josephson
tunneling between identical high temperature superconductors twisted an angle
about the c-axis. We model the tunneling matrix element squared as a
Gaussian in the change of wavevector q parallel to the junction, . The
obtained for the s- and extended-s-wave order parameters (OP's) are consistent
with the BiSrCaCuO data of Li {\it et al.}, but only
for strongly incoherent tunneling, . A -wave OP
is always inconsistent with the data. In addition, we show that the apparent
conventional sum rule violation observed by Basov et al. might be
understandable in terms of incoherent c-axis tunneling, provided that the OP is
not -wave.Comment: 6 pages, 6 figure
Top Squarks and Bottom Squarks in the MSSM with Complex Parameters
We present a phenomenological study of top squarks (~t_1,2) and bottom
squarks (~b_1,2) in the Minimal Supersymmetric Standard Model (MSSM) with
complex parameters A_t, A_b, \mu and M_1. In particular we focus on the CP
phase dependence of the branching ratios of (~t_1,2) and (~b_1,2) decays. We
give the formulae of the two-body decay widths and present numerical results.
We find that the effect of the phases on the (~t_1,2) and (~b_1,2) decays can
be quite significant in a large region of the MSSM parameter space. This could
have important implications for (~t_1,2) and (~b_1,2) searches and the MSSM
parameter determination in future collider experiments. We have also estimated
the accuracy expected in the determination of the parameters of ~t_i and ~b_i
by a global fit of the measured masses, decay branching ratios and production
cross sections at e^+ e^- linear colliders with polarized beams. Analysing two
scenarios, we find that the fundamental parameters apart from A_t and A_b can
be determined with errors of 1% to 2%, assuming an integrated luminosity of 1
ab^-1 and a sufficiently large c.m.s. energy to produce also the heavier ~t_2
and ~b_2 states. The parameter A_t can be determined with an error of 2 - 3%,
whereas the error on A_b is likely to be of the order of 50%.Comment: 31 pages, 8 figures, comments and references added, conclusions
unchanged; version to appear in Phys. Rev.
Relativistically invariant analysis of --isobar production in deuteron electrodisintegration: general analysis of polarization effects
The differential cross section and the polarization observables for --isobar production in the deuteron electrodisintegration process, , are calculated in a general formalism based on structure
functions. The obtained expressions have a general nature, hold for
one--photon--exchange, assuming P--invariance of the electromagnetic
interaction and the conservation of the hadron electromagnetic current. The
dependence of the differential cross section of the
reaction on the vector and tensor polarizations of the deuteron target with
unpolarized and longitudinally polarized electrons is considered. The general
dependence of the asymmetries on two of five kinematic variables, the azimuthal
angle and (linear polarization of the virtual photon) is
calculated. A similar analysis is performed for the polarization of the nucleon
produced in reaction provided the electron beam is
unpolarized or longitudinally polarized. Polarization effects, which are due to
the strong interaction in the final state are calculated. The
photoproduction of the --isobar on the deuteron target has been
considered in detail, as a particular case. The differential cross section and
various polarization observables have been derived in terms of the reaction
amplitudes. The polarization observables due to the linear and circular
polarizations of the photon, when the deuteron target is arbitrarily polarized
have been derived in terms of the reaction amplitudes. The polarization of the
final nucleon is also considered.Comment: 52 page
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
Recovering Joys Law as a Function of Solar Cycle, Hemisphere, and Longitude
Bipolar active regions in both hemispheres tend to be tilted with respect to
the East West equator of the Sun in accordance with Joys law that describes the
average tilt angle as a function of latitude. Mt. Wilson observatory data from
1917 to 1985 are used to analyze the active-region tilt angle as a function of
solar cycle, hemisphere, and longitude, in addition to the more common
dependence on latitude. Our main results are as follows: i) We recommend a
revision of Joys law toward a weaker dependence on latitude (slope of 0.13 to
0.26) and without forcing the tilt to zero at the Equator. ii) We determine
that the hemispheric mean tilt value of active regions varies with each solar
cycle, although the noise from a stochastic process dominates and does not
allow for a determination of the slope of Joys law on an 11-year time scale.
iii) The hemispheric difference in mean tilt angles, 1.1 degrees + 0.27, over
Cycles 16 to 21 was significant to a three-sigma level, with average tilt
angles in the northern and southern hemispheres of 4.7 degrees + 0.26 and 3.6
degrees + 0.27 respectively. iv) Area-weighted mean tilt angles normalized by
latitude for Cycles 15 to 21 anticorrelate with cycle strength for the southern
hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig,
Solanki, Krivova, et al. (2010, Astron. Astrophys. 518, A7). The northern
hemispheric mean tilt angles do not show a dependence on cycle strength. vi)
Mean tilt angles do not show a dependence on longitude for any hemisphere or
cycle. In addition, the standard deviation of the mean tilt is 29 to 31 degrees
for all cycles and hemispheres indicating that the scatter is due to the same
consistent process even if the mean tilt angles vary.Comment: 13 pages, 4 figures, 3 table
Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
We report a first measurement for ultra-high energy cosmic rays of the
correlation between the depth of shower maximum and the signal in the water
Cherenkov stations of air-showers registered simultaneously by the fluorescence
and the surface detectors of the Pierre Auger Observatory. Such a correlation
measurement is a unique feature of a hybrid air-shower observatory with
sensitivity to both the electromagnetic and muonic components. It allows an
accurate determination of the spread of primary masses in the cosmic-ray flux.
Up till now, constraints on the spread of primary masses have been dominated by
systematic uncertainties. The present correlation measurement is not affected
by systematics in the measurement of the depth of shower maximum or the signal
in the water Cherenkov stations. The analysis relies on general characteristics
of air showers and is thus robust also with respect to uncertainties in
hadronic event generators. The observed correlation in the energy range around
the `ankle' at differs significantly from
expectations for pure primary cosmic-ray compositions. A light composition made
up of proton and helium only is equally inconsistent with observations. The
data are explained well by a mixed composition including nuclei with mass . Scenarios such as the proton dip model, with almost pure compositions, are
thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray
flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report
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