1,591 research outputs found
On the Existence of Dynamics of Wheeler-Feynman Electromagnetism
We study the equations of Wheeler-Feynman electrodynamics which is an
action-at-a-distance theory about world-lines of charges that interact through
their corresponding advanced and retarded Li\'enard-Wiechert field terms. The
equations are non-linear, neutral, and involve time-like advanced as well as
retarded arguments of unbounded delay. Using a reformulation in terms of
Maxwell-Lorentz electrodynamics without self-interaction, which we have
introduced in a preceding work, we are able to establish the existence of
conditional solutions. These are solutions that solve the Wheeler-Feynman
equations on any finite time interval with prescribed continuations outside of
this interval. As a byproduct we also prove existence and uniqueness of
solutions to the Synge equations on the time half-line for a given history of
charge trajectories.Comment: 45 pages, introduction revised, typos corrected, explanations adde
A multiple factor model for European stocks
We present an empirical study focusing on the estimation of a fundamental multi-factor model for a universe of European stocks. Following the approach of the BARRA model, we have adopted a cross-sectional methodology. The proportion of explained variance ranges from 7.3% to 66.3% in the weekly regressions with a mean of 32.9%. For the individual factors we give the percentage of the weeks when they yielded statistically significant influence on stock returns. The best explanatory power – apart from the dominant country factors – was found among the statistical constructs „success“ and „variability in markets“.Vorgestellt wird eine empirische Studie, welche die Schätzung eines fundamentalen Multi-Faktor-Modells für ein Universum europäischer Aktien beinhaltet. Als Methode wurde in Anlehnung an die Vorgehensweise im BARRA-Modell der Querschnittsanalyse der Vorzug gegeben. Der Anteil der erklärten Varianz beläuft sich in den wöchentlichen Regressionen auf 7,3% bis 66,3% bei einem Durchschnitt von 32,9%. Für die einzelnen Faktoren wird die Häufigkeit angegeben, mit der sie sich in den Regressionen signifikant erwiesen haben. Den höchsten Erklärungsgehalt im Untersuchungszeitraum hatten Länderfaktoren, aber auch Konstrukte wie „Success“ oder „Variability in Markets“
Maxwell-Lorentz Dynamics of Rigid Charges
We establish global existence and uniqueness of the dynamics of classical
electromagnetism with extended, rigid charges and fields which need not to be
square integrable. We consider also a modified theory of electromagnetism where
no self-fields occur. That theory and our results are crucial for approaching
the as yet unsolved problem of the general existence of dynamics of Wheeler
Feynman electromagnetism, which we shall address in the follow up paper.Comment: 32 pages, revised Introduction, typos correcte
Atom-molecule Rabi oscillations in a Mott insulator
We observe large-amplitude Rabi oscillations between an atomic and a
molecular state near a Feshbach resonance. The experiment uses 87Rb in an
optical lattice and a Feshbach resonance near 414 G. The frequency and
amplitude of the oscillations depend on magnetic field in a way that is well
described by a two-level model. The observed density dependence of the
oscillation frequency agrees with the theoretical expectation. We confirmed
that the state produced after a half-cycle contains exactly one molecule at
each lattice site. In addition, we show that for energies in a gap of the
lattice band structure, the molecules cannot dissociate
Collisional decay of 87Rb Feshbach molecules at 1005.8 G
We present measurements of the loss-rate coefficients K_am and K_mm caused by
inelastic atom-molecule and molecule-molecule collisions. A thermal cloud of
atomic 87Rb is prepared in an optical dipole trap. A magnetic field is ramped
across the Feshbach resonance at 1007.4 G. This associates atom pairs to
molecules. A measurement of the molecule loss at 1005.8 G yields K_am=2 10^-10
cm^3/s. Additionally, the atoms can be removed with blast light. In this case,
the measured molecule loss yields K_mm=3 10^-10 cm^3/s
On the exit statistics theorem of many particle quantum scattering
We review the foundations of the scattering formalism for one particle
potential scattering and discuss the generalization to the simplest case of
many non interacting particles. We point out that the "straight path motion" of
the particles, which is achieved in the scattering regime, is at the heart of
the crossing statistics of surfaces, which should be thought of as detector
surfaces. We sketch a proof of the relevant version of the many particle flux
across surfaces theorem and discuss what needs to be proven for the foundations
of scattering theory in this context.Comment: 15 pages, 4 figures; to appear in the proceedings of the conference
"Multiscale methods in Quantum Mechanics", Accademia dei Lincei, Rome,
December 16-20, 200
Combination of a magnetic Feshbach resonance and an optical bound-to-bound transition
We use laser light near resonant with an optical bound-to-bound transition to
shift the magnetic field at which a Feshbach resonance occurs. We operate in a
regime of large detuning and large laser intensity. This reduces the
light-induced atom-loss rate by one order of magnitude compared to our previous
experiments [D.M. Bauer et al. Nature Phys. 5, 339 (2009)]. The experiments are
performed in an optical lattice and include high-resolution spectroscopy of
excited molecular states, reported here. In addition, we give a detailed
account of a theoretical model that describes our experimental data
Bohmian Mechanics and Quantum Information
Many recent results suggest that quantum theory is about information, and
that quantum theory is best understood as arising from principles concerning
information and information processing. At the same time, by far the simplest
version of quantum mechanics, Bohmian mechanics, is concerned, not with
information but with the behavior of an objective microscopic reality given by
particles and their positions. What I would like to do here is to examine
whether, and to what extent, the importance of information, observation, and
the like in quantum theory can be understood from a Bohmian perspective. I
would like to explore the hypothesis that the idea that information plays a
special role in physics naturally emerges in a Bohmian universe.Comment: 25 pages, 2 figure
Time and Ensemble Averages in Bohmian Mechanics
We show that in the framework of one-dimensional Bohmian Quantum
Mechanics[1], for a particle subject to a potential undergoing a weak adiabatic
change, the time averages of the particle's positions typically differ markedly
from the ensemble averages. We Apply this result to the case where the weak
perturbing potential is the back-action of a measuring device (i.e. a
protective measurement). It is shown that under these conditions, most
trajectories never cross the position measured (as already shown for a
particular example in [3]).Comment: 6 page
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