3,200 research outputs found
Why Is It So Difficult to Beat the Random Walk Forecast of Exchange Rates?
We propose a stylized exchange rate model based on diversity and weight of opinion. Our model departs from standard assumptions in that we allow for heterogeneous agents. We show that such a model can explain both the observed volatility and the persistence of real and nominal exchange rate movements and thus in some measure resolves Rogoff’s (1996) purchasing power parity puzzle. Our empirical analysis reconciles the well-known difficulties in beating the random walk forecast model with the statistical evidence of nonlinear mean reversion in deviations from fundamentals. We find strong evidence of long-horizon predictability both in theory and in practice. We also explain why it is difficult to exploit this predictability in out-ofsample forecasts. Our results not only lend support to economists’ beliefs that the exchange rate is inherently predictable, but they also help us to understand the reluctance of applied forecasters to abandon chartists methods in favor of models based on economic fundamentals.Purchasing power parity, Real exchange rate, Random walk, Economic models of exchange rate determination, Long-horizon regression tests.
Local spin polarization in underdoped cuprates with impurities
We present a theory of magnetic (Ni) and nonmagnetic (Zn) impurities
substituted into planar Cu sites in the normal state of underdoped cuprates
exhibiting a spin gap. Both types of impurities induce magnetic moments on
neighboring Cu sites. In the case of Ni these moments partially screen the
inherent impurity spin, resulting in an effective S=1/2 moment. The
characteristic Kondo scale is found to have a power-law dependence on the
coupling constant. We investigate the spatial shape of the impurity-induced
spin density, taking into account the presence of short-ranged AF correlations,
and calculate the ^{17}O NMR line broadening induced by impurity doping.Comment: To appear in: Physica C, Proceedings of ACS '9
The Reconstruction of Trilinear Higgs Couplings
To establish the Higgs mechanism {\it sui generis} experimentally, the Higgs
self-interaction potential must be reconstructed. This task requires the
measurement of the trilinear and quadrilinear self-couplings, as predicted in
the Standard Model or in supersymmetric theories. The couplings can be probed
in multiple Higgs production at high-luminosity e+e- linear colliders. We
present the theoretical analysis for the production of neutral Higgs-boson
pairs in the relevant channels of double Higgs-strahlung and associated
multiple Higgs production.Comment: 20 pages, Proceedings, "Physics with a High-Luminosity e+e- Linear
Collider", DESY/ECFA LC Workshop, DESY 99-123
Unitarization of monodromy representations and constant mean curvature trinoids in 3-dimensional space forms
We present a theorem on the unitarizability of loop group valued monodromy
representations and apply this to show the existence of new families of
constant mean curvature surfaces homeomorphic to a thrice-punctured sphere in
the simply-connected 3-dimensional space forms , \bbS^3 and \bbH^3.
Additionally, we compute the extended frame for any associated family of
Delaunay surfaces.Comment: 18 pages, revised versio
Production of Neutral Higgs-Boson Pairs at LHC
The reconstruction of the Higgs potential in the Standard Model or
supersymmetric theories demands the measurement of the trilinear Higgs
couplings. These couplings affect the multiple production of Higgs bosons at
high energy colliders. We present a systematic overview of the cross sections
for the production of pairs of (light) neutral Higgs bosons at the LHC. The
analysis is carried out for the Standard Model and its minimal supersymmetric
extension.Comment: Latex, 11 pages, uses feynmp.sty [included]. The complete paper,
including figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-17/ or via www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints
Testing Higgs Self-couplings at e^+e^- Linear Colliders
To establish the Higgs mechanism sui generis experimentally, the self-energy
potential of the Higgs field must be reconstructed. This task requires the
measurement of the trilinear and quadrilinear self-couplings, as predicted, for
instance, in the Standard Model or in supersymmetric theories. The couplings
can be probed in multiple Higgs production at high-luminosity e^+e^- linear
colliders. Complementing earlier studies to develop a coherent picture of the
trilinear couplings, we have analyzed the production of pairs of neutral Higgs
bosons in all relevant channels of double Higgs-strahlung, associated multiple
Higgs production and WW/ZZ fusion to Higgs pairs.Comment: The complete paper, including figures, is also available via
anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-02/ or via
www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/webmaster/preprints
Constant mean curvature surfaces of any positive genus
We show the existence of several new families of non-compact constant mean
curvature surfaces: (i) singly-punctured surfaces of arbitrary genus , (ii) doubly-punctured tori, and (iii) doubly periodic surfaces with
Delaunay ends.Comment: 14 pages, 10 figure
A hybrid model for Rydberg gases including exact two-body correlations
A model for the simulation of ensembles of laser-driven Rydberg-Rydberg
interacting multi-level atoms is discussed. Our hybrid approach combines an
exact two-body treatment of nearby atom pairs with an effective approximate
treatment for spatially separated pairs. We propose an optimized evolution
equation based only on the system steady state, and a time-independent Monte
Carlo technique is used to efficiently determine this steady state. The hybrid
model predicts features in the pair correlation function arising from
multi-atom processes which existing models can only partially reproduce. Our
interpretation of these features shows that higher-order correlations are
relevant already at low densities. Finally, we analyze the performance of our
model in the high-density case.Comment: significantly expanded and revised version (more observables,
high-density regime); 9 pages, 8 figure
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