3,134 research outputs found
Locality and topology in the molecular Aharonov-Bohm effect
It is shown that the molecular Aharonov-Bohm effect is neither nonlocal nor
topological in the sense of the standard magnetic Aharonov-Bohm effect. It is
further argued that there is a close relationship between the molecular
Aharonov-Bohm effect and the Aharonov-Casher effect for an electrically neutral
spin particle encircling a line of charge.Comment: 3 pages, no figure
Coupling SPH and thermochemical models of planets: Methodology and example of a Mars-sized body
Giant impacts have been suggested to explain various characteristics of
terrestrial planets and their moons. However, so far in most models only the
immediate effects of the collisions have been considered, while the long-term
interior evolution of the impacted planets was not studied. Here we present a
new approach, combining 3-D shock physics collision calculations with 3-D
thermochemical interior evolution models. We apply the combined methods to a
demonstration example of a giant impact on a Mars-sized body, using typical
collisional parameters from previous studies. While the material parameters
(equation of state, rheology model) used in the impact simulations can have
some effect on the long-term evolution, we find that the impact angle is the
most crucial parameter for the resulting spatial distribution of the newly
formed crust. The results indicate that a dichotomous crustal pattern can form
after a head-on collision, while this is not the case when considering a more
likely grazing collision. Our results underline that end-to-end 3-D
calculations of the entire process are required to study in the future the
effects of large-scale impacts on the evolution of planetary interiors.Comment: 29 pages, 10 figures, accepted for publication in Icaru
Correlated two-photon emission by transitions of Dirac-Volkov states in intense laser fields: QED predictions
In an intense laser field, an electron may decay by emitting a pair of
photons. The two photons emitted during the process, which can be interpreted
as a laser-dressed double Compton scattering, remain entangled in a
quantifiable way: namely, the so-called concurrence of the photon polarizations
gives a gauge-invariant measure of the correlation of the hard gamma rays. We
calculate the differential rate and concurrence for a backscattering setup of
the electron and photon beam, employing Volkov states and propagators for the
electron lines, thus accounting nonperturbatively for the electron-laser
interaction. The nonperturbative results are shown to differ significantly
compared to those obtained from the usual double Compton scattering.Comment: 32 pages, 12 figure
Searching for degeneracies of real Hamiltonians using homotopy classification of loops in SO()
Topological tests to detect degeneracies of Hamiltonians have been put
forward in the past. Here, we address the applicability of a recently proposed
test [Phys. Rev. Lett. {\bf 92}, 060406 (2004)] for degeneracies of real
Hamiltonian matrices. This test relies on the existence of nontrivial loops in
the space of eigenbases SO. We develop necessary means to determine the
homotopy class of a given loop in this space. Furthermore, in cases where the
dimension of the relevant Hilbert space is large the application of the
original test may not be immediate. To remedy this deficiency, we put forward a
condition for when the test is applicable to a subspace of Hilbert space.
Finally, we demonstrate that applying the methodology of [Phys. Rev. Lett. {\bf
92}, 060406 (2004)] to the complex Hamiltonian case does not provide any new
information.Comment: Minor changes, journal reference adde
Sufficient Conditions for Fast Switching Synchronization in Time Varying Network Topologies
In previous work, empirical evidence indicated that a time-varying network
could propagate sufficient information to allow synchronization of the
sometimes coupled oscillators, despite an instantaneously disconnected
topology. We prove here that if the network of oscillators synchronizes for the
static time-average of the topology, then the network will synchronize with the
time-varying topology if the time-average is achieved sufficiently fast. Fast
switching, fast on the time-scale of the coupled oscillators, overcomes the
descychnronizing decoherence suggested by disconnected instantaneous networks.
This result agrees in spirit with that of where empirical evidence suggested
that a moving averaged graph Laplacian could be used in the master-stability
function analysis. A new fast switching stability criterion here-in gives
sufficiency of a fast-switching network leading to synchronization. Although
this sufficient condition appears to be very conservative, it provides new
insights about the requirements for synchronization when the network topology
is time-varying. In particular, it can be shown that networks of oscillators
can synchronize even if at every point in time the frozen-time network topology
is insufficiently connected to achieve synchronization.Comment: Submitted to SIAD
Canonical Timing and Spectral Behavior of LMC X-3 in the Low/Hard State
We present results from three observations with the Rossi X-ray Timing
Explorer (RXTE) of LMC X-3, obtained while the source was in an extended
'low/hard' state. The data reveal a hard X-ray spectrum which is well fit by a
pure power law with photon index Gamma=1.69+/-0.02, with a source luminosity at
50 kpc of 5-16x10^{36}erg/s (2--10 keV). Strong broad-band (0.01-100 Hz) time
variability is also observed, with fractional rms amplitude 40+/-4%, plus a
quasi-periodic oscillation (QPO) peak at 0.46+/-0.02 Hz with rms amplitude
\~14%. This is the first reported observation in which the full canonical
low/hard state behavior (pure hard power law spectrum combined with strong
broad-band noise and QPO) for LMC X-3 is seen. We reanalyze several archival
RXTE observations of LMC X-3 and derive consistent spectral and timing
parameters, and determine the overall luminosity variation between high/soft
and low/hard states. The timing and spectral properties of LMC X-3 during the
recurrent low/hard states are quantitatively similar to that typically seen in
the Galactic black hole candidates.Comment: 5 pages, 3 figures, accepted for ApJ Letter
Action and Hamiltonian for eternal black holes
We present the Hamiltonian, quasilocal energy, and angular momentum for a
spacetime region spatially bounded by two timelike surfaces. The results are
applied to the particular case of a spacetime representing an eternal black
hole. It is shown that in the case when the boundaries are located in two
different wedges of the Kruskal diagram, the Hamiltonian is of the form , where and are the Hamiltonian functions for the right
and left wedges respectively. The application of the obtained results to the
thermofield dynamics description of quantum effects in black holes is briefly
discussed.Comment: 24 pages, Revtex, 5 figures (available upon request
Border Collision Route to Quasiperiodicity: Numerical Investigation and Experimental Confirmation
Numerical studies of higher-dimensional piecewise-smooth systems have recently shown how a torus can arise from a periodic cycle through a special type of border-collision bifurcation. The present article investigates this new route to quasiperiodicity in the two-dimensional piecewise-linear normal form map. We have obtained the chart of the dynamical modes for this map and showed that border-collision bifurcations can lead to the birth of a stable closed invariant curve associated with quasiperiodic or periodic dynamics. In the parameter regions leading to the existence of an invariant closed curve, there may be transitions between an ergodic torus and a resonance torus, but the mechanism of creation for the resonance tongues is distinctly different from that observed in smooth maps. The transition from a stable focus point to a resonance torus may lead directly to a new focus of higher periodicity, e.g., a period-5 focus. This article also contains a discussion of torus destruction via a homoclinic bifurcation in the piecewise-linear normal map. Using a dc-dc converter with two-level control as an example, we report the first experimental verification of the direct transition to quasiperiodicity through a border-collision bifurcation
S(k) for Haldane Gap Antiferromagnets: Large-scale Numerical Results vs. Field Theory and Experiment
The structure function, S(k), for the s=1, Haldane gap antiferromagnetic
chain, is measured accurately using the recent density matrix renormalization
group method, with chain-length 100. Excellent agreement with the nonlinear
model prediction is obtained, both at where a single
magnon process dominates and at where a two magnon process
dominates. We repeat our calculation with crystal field anisotropy chosen to
model NENP, obtaining good agreement with both field theory predictions and
recent experiments. Correlation lengths, gaps and velocities are determined for
both polarizations.Comment: 11 pages, 3 postscript figures included, REVTEX 3.0, UBCTP-93-02
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