1,443 research outputs found
Pairs Trading: A Cointegration Approach
This study uses the Johansen test for cointegration to select trading pairs for use within a pairs trading framework. A long-run equilibrium price relationship is then estimated for the identified trading pairs, and the resulting mean-reverting residual spread is modeled as a Vector-Error-Correction model (VECM). The study uses 5 years of daily stock prices starting from the beginning of July, 2002. The search for trading pairs is restricted to 17 financial stocks listed on the ASX200. The results show that two cointegrated stocks can be combined in a certain linear combination so that the dynamics of the resulting portfolio are governed by a stationary process. Although a trading rule is not employed to access the profitability of this trading strategy, plots of the residual series show a high rate of zero crossings and large deviations around the mean. This would suggest that this strategy would likely be profitable. It can also be concluded that in the presence of cointegration, at least one of the speed of adjustment coefficients must be significantly different from zero
Analytic Amplitudes for Hadronic Forward Scattering : COMPETE Update
We consider several classes of analytic parametrizations of hadronic
scattering amplitudes, and compare their predictions to all available forward
data in hadron-hadron, gamma-p and gamma-gamma reactions. Although these
parametrizations are very close for SQRTs larger than 9 GeV, it turns out that
they differ markedly at low energy, where a universal Pomeron term like ln**2 s
enables one to extend the fit down to SQRTs equal to 4 GeV. We present
predictions on the total cross sections and on the ratio of the real part to
the imaginary part of the elastic amplitude (RHO parameter) for present and
future pp and antipp colliders, and on total cross sections for gamma-p into
hadrons at cosmic-ray energies and for gamma-gamma into hadrons up to SQRTs
equal to 1 TeV.Comment: 3 pages, 3 tables. To be published in the Proceedings of the 31st
International Conference on High Energy Physics (ICHEP 2002), Amsterdam, The
Netherlands, 24-31 July 200
Higgs Boson Bounds in Three and Four Generation Scenarios
In light of recent experimental results, we present updated bounds on the
lightest Higgs boson mass in the Standard Model (SM) and in the Minimal
Supersymmetric extension of the Standard Model (MSSM). The vacuum stability
lower bound on the pure SM Higgs boson mass when the SM is taken to be valid up
to the Planck scale lies above the MSSM lightest Higgs boson mass upper bound
for a large amount of SUSY parameter space. If the lightest Higgs boson is
detected with a mass M_{H} < 134 GeV (150 GeV) for a top quark mass M_{top} =
172 GeV (179 GeV), it may indicate the existence of a fourth generation of
fermions. The region of inconsistency is removed and the MSSM is salvagable for
such values of M_{H} if one postulates the existence of a fourth generation of
leptons and quarks with isodoublet degenerate masses M_{L} and M_{Q} such that
60 GeV 170 GeV.Comment: 7 pages, 4 figures. To be published in Physical Review
Investigations of the pi N total cross sections at high energies using new FESR: log nu or (log nu)^2
We propose to use rich informations on pi p total cross sections below N= 10
GeV in addition to high-energy data in order to discriminate whether these
cross sections increase like log nu or (log nu)^2 at high energies, since it is
difficult to discriminate between asymptotic log nu and (log nu)^2 fits from
high-energy data alone. A finite-energy sum rule (FESR) which is derived in the
spirit of the P' sum rule as well as the n=1 moment FESR have been required to
constrain the high-energy parameters. We then searched for the best fit of pi p
total cross sections above 70 GeV in terms of high-energy parameters
constrained by these two FESR. We can show from this analysis that the (log
nu)^2 behaviours is preferred to the log nu behaviours.Comment: to be published in Phys. Rev. D 5 pages, 2 eps figure
Photoemission and x-ray absorption spectroscopy study of electron-doped colossal magnetoresistance manganite: La0.7Ce0.3MnO3 film
The electronic structure of La0.7Ce0.3MnO3 (LCeMO) thin film has been
investigated using photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). The Ce 3d core-level PES and XAS spectra of LCeMO are very
similar to those of CeO2, indicating that Ce ions are far from being trivalent.
A very weak 4f resonance is observed around the Ce 4d 4f absorption edge,
suggesting that the localized Ce 4f states are almost empty in the ground
state. The Mn 2p XAS spectrum reveals the existence of the Mn(2+) multiplet
feature, confirming the Mn(2+)-Mn(3+) mixed-valent states of Mn ions in LCeMO.
The measured Mn 3d PES/XAS spectra for LCeMO agrees reasonably well with the
calculated Mn 3d PDOS using the LSDA+U method. The LSDA+U calculation predicts
a half-metallic ground state for LCeMO.Comment: 7 pages, 7 figure
Suppression of Superconducting Critical Current Density by Small Flux Jumps in Thin Films
By doing magnetization measurements during magnetic field sweeps on thin
films of the new superconductor , it is found that in a low temperature
and low field region small flux jumps are taking place. This effect strongly
suppresses the central magnetization peak leading to reduced nominal
superconducting critical current density at low temperatures. A borderline for
this effect to occur is determined on the field-temperature (H-T) phase
diagram. It is suggested that the small size of the flux jumps in films is due
to the higher density of small defects and the relatively easy thermal
diffusion in thin films in comparison with bulk samples.Comment: 7 figures Phys. Rev. B accepted scheduled issue: 01 Feb 200
Nearly degenerate neutrinos, Supersymmetry and radiative corrections
If neutrinos are to play a relevant cosmological role, they must be
essentially degenerate with a mass matrix of the bimaximal mixing type. We
study this scenario in the MSSM framework, finding that if neutrino masses are
produced by a see-saw mechanism, the radiative corrections give rise to mass
splittings and mixing angles that can accommodate the atmospheric and the
(large angle MSW) solar neutrino oscillations. This provides a natural origin
for the hierarchy. On the other hand,
the vacuum oscillation solution to the solar neutrino problem is always
excluded. We discuss also in the SUSY scenario other possible effects of
radiative corrections involving the new neutrino Yukawa couplings, including
implications for triviality limits on the Majorana mass, the infrared fixed
point value of the top Yukawa coupling, and gauge coupling and bottom-tau
unification.Comment: 32 pages, 12 Postscript figures, uses psfig.st
Bulk experimental evidence of half-metallic ferromagnetism in doped manganites
We report precise measurements and quantitative data analysis on the
low-temperature resistivity of several ferromagnetic manganite films. We
clearly show that there exists a T^{4.5} term in low-temperature resistivity,
and that this term is in quantitative agreement with the quantum theory of
two-magnon scattering for half metallic ferromagnets. Our present results
provide the first bulk experimental evidence of half-metallic ferromagnetism in
doped manganites.Comment: 4 pages, 4 figure
Naturalness of nearly degenerate neutrinos
If neutrinos are to play a relevant cosmological role, they must be
essentially degenerate. We study whether radiative corrections can or cannot be
responsible for the small mass splittings, in agreement with all the available
experimental data. We perform an exhaustive exploration of the bimaximal mixing
scenario, finding that (i) the vacuum oscillations solution to the solar
neutrino problem is always excluded; (ii) if the mass matrix is produced by a
see-saw mechanism, there are large regions of the parameter space consistent
with the large angle MSW solution, providing a natural origin for the hierarchy; (iii) the bimaximal structure becomes
then stable under radiative corrections. We also provide analytical expressions
for the mass splittings and mixing angles and present a particularly simple
see-saw ansatz consistent with all observations.Comment: 25 pages, LaTeX, 6 ps figures, psfig.sty. Typos, references and minor
details corrected. Additional condition for the MSW mechanism incorporated.
New viable textures adde
Electromigration-Induced Flow of Islands and Voids on the Cu(001) Surface
Electromigration-induced flow of islands and voids on the Cu(001) surface is
studied at the atomic scale. The basic drift mechanisms are identified using a
complete set of energy barriers for adatom hopping on the Cu(001) surface,
combined with kinetic Monte Carlo simulations. The energy barriers are
calculated by the embedded atom method, and parameterized using a simple model.
The dependence of the flow on the temperature, the size of the clusters, and
the strength of the applied field is obtained. For both islands and voids it is
found that edge diffusion is the dominant mass-transport mechanism. The rate
limiting steps are identified. For both islands and voids they involve
detachment of atoms from corners into the adjacent edge. The energy barriers
for these moves are found to be in good agreement with the activation energy
for island/void drift obtained from Arrhenius analysis of the simulation
results. The relevance of the results to other FCC(001) metal surfaces and
their experimental implications are discussed.Comment: 9 pages, 13 ps figure
- …