540 research outputs found
Exchange rate predictability in a changing world
An expanding literature articulates the view that Taylor rules are helpful in predicting exchange rates. In a changing world, however, Taylor rule parameters may be subject to structural instabilities, for example in the aftermath of the Global Financial Crisis. This paper forecasts exchange rates using Taylor rules with Time-Varying Parameters (TVP) estimated by Bayesian methods. Focusing on the data from the crisis, we improve upon the random walk for at least half, and for as many as seven out of 10, of the currencies considered. Results are stronger when we allow the TVP of the Taylor rules to differ between countries
Dealing with Uncertainties in Asteroid Deflection Demonstration Missions: NEOTwIST
Deflection missions to near-Earth asteroids will encounter non-negligible
uncertainties in the physical and orbital parameters of the target object. In
order to reliably assess future impact threat mitigation operations such
uncertainties have to be quantified and incorporated into the mission design.
The implementation of deflection demonstration missions offers the great
opportunity to test our current understanding of deflection relevant
uncertainties and their consequences, e.g., regarding kinetic impacts on
asteroid surfaces. In this contribution, we discuss the role of uncertainties
in the NEOTwIST asteroid deflection demonstration concept, a low-cost kinetic
impactor design elaborated in the framework of the NEOShield project. The aim
of NEOTwIST is to change the spin state of a known and well characterized
near-Earth object, in this case the asteroid (25143) Itokawa. Fast events such
as the production of the impact crater and ejecta are studied via cube-sat
chasers and a flyby vehicle. Long term changes, for instance, in the asteroid's
spin and orbit, can be assessed using ground based observations. We find that
such a mission can indeed provide valuable constraints on mitigation relevant
parameters. Furthermore, the here proposed kinetic impact scenarios can be
implemented within the next two decades without threatening Earth's safety.Comment: Accepted for publication in the proceedings of the IAUS 318 -
Asteroids: New Observations, New Models, held at the IAU General Assembly in
Honolulu, Hawaii, USA 201
Diffractive Photoproduction of Eta_c
Diffractive photoproduction of is an important process to study the
effect of Odderon, whose existence is still not confirmed in experiment. A
detailed interpretation of Odderon in QCD, i.e., in terms of gluons is also
unclear.Taking charm quarks as heavy quarks, we can use NRQCD and take
as a bound state. Hence, in the production of a free pair is first produced and this pair is transformed into
subsequently.In the forward region of the kinematics, the pair
interacts with initial hadron through exchanges of soft gluons. This
interaction can be studied with HQET, which provides a systematic expansion in
the inverse of the -quark mass . We find that the calculation of the
-matrix element in the forward region can be formulated as the problem of
solving a wave function of a -quark propagating in a background field of
soft gluons. At leading order we find that the differential cross-section can
be expressed with four functions, which are defined with a twist-3 operator of
gluons. The effect of exchanging a Odderon can be identified with this operator
in our case. We discuss our results in detail and compare them with those
obtained in previous studies. Our results and those from other studies show
that the differential cross-section is very small in the forward region. We
also show that the production through photon exchange is dominant in the
extremely forward region, hence the effect of Odderon exchange can not be
identified in this region.For completeness we also give results for diffractive
photoproduction of .Comment: 20 pages with 3 figures. Text improve
Model selection with estimated factors and idiosyncratic components
This paper provides consistent information criteria for the selection of forecasting models which use a subset of both the idiosyncratic and common factor components of a big dataset. This hybrid model approach has been explored by recent empirical studies to relax the strictness of pure factor-augmented model approximations, but no formal model selection procedures have been developed. The main difference to previous factor-augmented model selection procedures is that we must account for estimation error in the idiosyncratic component as well as the factors. Our main contribution is to show the conditions required for selection consistency of a class of information criteria which reflect this additional source of estimation error. We show that existing factor-augmented model selection criteria are inconsistent in circumstances where N is of larger order than root-T, where N and T are the cross-section and time series dimensions of the dataset respectively, and that the standard BIC is inconsistent regardless of the relationship between N and T. We therefore propose a new set of information criteria which guarantee selection consistency in the presence of estimated idiosyncratic components. The properties of these new criteria are explored through a Monte Carlo simulation study. The paper concludes with an empirical application to long-horizon exchange rate forecasting using a recently proposed model with country-specific idiosyncratic components from a panel of global exchange rates
Hidden Behind the Wall: West German State Building and the Emergence of the Iron Curtain
It is widely accepted that the inter-German border was constructed by East German authorities to halt the emigration to the west, which had damaged the East German economy and undermined the East German state agencies' power. This article argues that this is an inaccurate understanding, which mistakenly treats perceptions and insights gained from studying the Berlin Wall as representative of the mostly rural border between East and West Germany. It emphasizes crucial transformations of frontier society during the 1950s, highlighting the important role of western as well as eastern policy in shaping them
Are CDS spreads predictable? An analysis of linear and non-linear forecasting models
We assess the statistical and economic performance of various forecasting models to predict the future values of the iTraxx index. We find that linear models outperform non-linear models out-of-sample. Some trading strategies based on forecasts generated by the linear models deliver positive Sharpe ratios
Possible probe of the QCD odderon singularity through the quasidiffractive eta_c production in gamma-gamma collisions
The reactions gamma-gamma to eta_c eta_c and gamma gamma to eta_c + X are
discussed within the three gluon exchange model. We give predictions for the
differential cross-sections and discuss feasibility of measuring these
processes at LEP2 and TESLA. The total cross-sections were estimated to be
approximately equal to 40 fb and 120 fb for gamma-gamma to eta_c eta_c and
gamma-gamma to eta_c + X respectively assuming exchange of elementary gluons
that corresponds to the odderon with intercept equal to unity. These values can
be enhanced by a factor equal to 1.9 and 2.1 for LEP2 and TESLA energies if the
odderon intercept is equal to 1.07. The estimate of cross-sections sigma(e^+
e^- to e^+ e^- eta_c eta_c) and sigma (e^+ e^- to e^+ e^- eta_c + X) for
untagged e^+ and e^- is also given.Comment: 11 pages, Latex, epsf, 5 eps figures include
Close-to-threshold Meson Production in Hadronic Interactions
Studies of meson production at threshold in the hadron--hadron interaction
began in the fifties when sufficient energies of accelerated protons were
available. A strong interdependence between developments in accelerator
physics, detector performance and theoretical understanding led to a unique
vivid field of physics. Early experiments performed with bubble chambers
revealed already typical ingredients of threshold studies, which were
superseded by more complete meson production investigations at the nucleon beam
facilities TRIUMF, LAMPF, PSI, LEAR and SATURNE. Currently, with the advent of
the new cooler rings as IUCF, CELSIUS and COSY the field is entering a new
domain of precision and the next step of further progress.
The analysis of this new data in the short range limit permits a more
fundamental consideration and a quantitative comparison of the production
processes for different mesons in the few--body final states. The
interpretation of the data take advantage of the fact that production reactions
close-to-threshold are characterized by only a few degrees of freedom between a
well defined combination of initial and exit channels. Deviations from
predictions of phase-space controlled one-meson-exchange models are indications
of new and exciting physics. Precision data on differential cross sections,
isospin and spin observables -- partly but by no means adequately available --
are presently turning up on the horizon. There is work for the next years and
excitement of the physics expected. Here we try to give a brief and at the same
time comprehensive overview of this field of hadronic threshold production
studies.Comment: 100 pages, Review article to be published in Prog. Part. Nucl. Phys.
Vol. 49, issue 1 (2002
Precision tau physics
Precise measurements of the lepton properties provide stringent tests of the Standard Model and accurate determinations of its parameters. We overview the present status of tau physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the tau lepton probe the structure of the weak currents and the universality of their couplings to the W boson. The universality of the leptonic Z couplings has also been tested through Z -> l(+)l(-) decays. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interaction in very clean conditions. Accurate determinations of the QCD coupling and the Cabibbo mixing V-us have been obtained with tau data. The large mass of the tau opens the possibility to study many kinematically-allowed exclusive decay modes and extract relevant dynamical information. Violations of flavour and CP conservation laws can also be searched for with tau decays. Related subjects such as μdecays, the electron and muon anomalous magnetic moments, neutrino mixing and B-meson decays into tau leptons are briefly covered. Being one the fermions most strongly coupled to the scalar sector, the tau lepton is playing now a very important role at the LHC as a tool to test the Higgs properties and search for new physics at higher scales
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