36,534 research outputs found
Classical radiation by free-falling charges in de Sitter spacetime
We study the classical radiation emitted by free-falling charges in de Sitter
spacetime coupled to different kinds of fields. Specifically we consider the
cases of the electromagnetic field, linearized gravity and scalar fields with
arbitrary mass and curvature coupling. Given an arbitrary set of such charges,
there is a generic result for sufficiently late times which corresponds to each
charge being surrounded by a field zone with negligible influence from the
other charges. Furthermore, we explicitly find a static solution in the static
patch adapted to a charge (implying no energy loss by the charge) which can be
regularly extended beyond the horizon to the full de Sitter spacetime, and show
that any other solution decays at late times to this one. On the other hand,
for non-conformal scalar fields the inertial observers naturally associated
with spatially flat coordinates will see a non-vanishing flux far from the
horizon, which will fall off more slowly than the inverse square of the
distance for sufficiently light fields (m^2 + \xi R < 5H^2/4) and give rise to
a total integrated flux that grows unboundedly with the radius. This can be
qualitatively interpreted as a consequence of a classical parametric
amplification of the field generated by the charge due to the time-dependent
background spacetime. Most of these results do not hold for massless minimally
coupled scalar fields, whose special behavior is analyzed separately.Comment: 31 pages, REVTeX4, minor changes, one reference added, version to
appear in Phys. Rev.
Monetary expansion and federal open market committee operating strategy in 1971
Federal Open Market Committee ; Monetary policy - United States
AGRICULTURAL TERRORISM: POTENTIAL ECONOMIC EFFECTS ON THE POULTRY INDUSTRY IN MISSISSIPPI
An input/output model was developed to estimate the potential economic impact of intentional attacks by agricultural terrorists using Exotic Newcastle Disease (END) on the poultry industry in Mississippi. The model measured impacts in terms of income, employment, output, and tax changes in the poultry industry.Risk and Uncertainty,
Modeling Light Trapping in Nanostructured Solar Cells
The integration of nanophotonic and plasmonic structures with solar cells offers the ability to control and confine light in nanoscale dimensions. These nanostructures can be used to couple incident sunlight into both localized and guided modes, enhancing absorption while reducing the quantity of material. Here we use electromagnetic modeling to study the resonances in a solar cell containing both plasmonic metal back contacts and nanostructured semiconductor top contacts, identify the local and guided modes contributing to enhanced absorption, and optimize the design. We then study the role of the different interfaces and show that Al is a viable plasmonic back contact material
Semiclassical approximation in Batalin-Vilkovisky formalism
The geometry of supermanifolds provided with -structure (i.e. with odd
vector field satisfying ), -structure (odd symplectic
structure ) and -structure (volume element) or with various combinations of
these structures is studied. The results are applied to the analysis of
Batalin-Vilkovisky approach to the quantization of gauge theories. In
particular the semiclassical approximation in this approach is expressed in
terms of Reidemeister torsion.Comment: 27 page
Quantum Rabi model for N-state atoms
A tractable N-state Rabi Hamiltonian is introduced by extending the parity
symmetry of the two-state model. The single-mode case provides a few-parameter
description of a novel class of periodic systems, predicting that the ground
state of certain four-state atom-cavity systems will undergo parity change at
strong coupling. A group-theoretical treatment provides physical insight into
dynamics and a modified rotating wave approximation obtains accurate analytical
energies. The dissipative case can be applied to study excitation energy
transfer in molecular rings or chains.Comment: 5 pages, 3 figures + supplement (2 pages); to appear in Phys. Rev.
Let
Geometry of Batalin-Vilkovisky quantization
The present paper is devoted to the study of geometry of Batalin-Vilkovisky
quantization procedure. The main mathematical objects under consideration are
P-manifolds and SP-manifolds (supermanifolds provided with an odd symplectic
structure and, in the case of SP-manifolds, with a volume element). The
Batalin-Vilkovisky procedure leads to consideration of integrals of the
superharmonic functions over Lagrangian submanifolds. The choice of Lagrangian
submanifold can be interpreted as a choice of gauge condition; Batalin and
Vilkovisky proved that in some sense their procedure is gauge independent. We
prove much more general theorem of the same kind. This theorem leads to a
conjecture that one can modify the quantization procedure in such a way as to
avoid the use of the notion of Lagrangian submanifold. In the next paper we
will show that this is really so at least in the semiclassical approximation.
Namely the physical quantities can be expressed as integrals over some set of
critical points of solution S to the master equation with the integrand
expressed in terms of Reidemeister torsion. This leads to a simplification of
quantization procedure and to the possibility to get rigorous results also in
the infinite-dimensional case. The present paper contains also a compete
classification of P-manifolds and SP-manifolds. The classification is
interesting by itself, but in this paper it plays also a role of an important
tool in the proof of other results.Comment: 13 page
Predicting the hypervelocity star population in Gaia
Hypervelocity stars (HVSs) are amongst the fastest objects in our Milky Way.
These stars are predicted to come from the Galactic center (GC) and travel
along unbound orbits across the Galaxy. In the coming years, the ESA satellite
Gaia will provide the most complete and accurate catalogue of the Milky Way,
with full astrometric parameters for more than billion stars. In this
paper, we present the expected sample size and properties (mass, magnitude,
spatial, velocity distributions) of HVSs in the Gaia stellar catalogue. We
build three Gaia mock catalogues of HVSs anchored to current observations,
exploring different ejection mechanisms and GC stellar population properties.
In all cases, we predict hundreds to thousands of HVSs with precise proper
motion measurements within a few tens of kpc from us. For stars with a relative
error in total proper motion below , the mass range extends to ~ but peaks at ~ . The majority of Gaia HVSs will
therefore probe a different mass and distance range compared to the current
non-Gaia sample. In addition, a subset of a few hundreds to a few thousands of
HVSs with ~ will be bright enough to have a precise
measurement of the three-dimensional velocity from Gaia alone. Finally, we show
that Gaia will provide more precise proper motion measurements for the current
sample of HVS candidates. This will help identifying their birthplace narrowing
down their ejection location, and confirming or rejecting their nature as HVSs.
Overall, our forecasts are extremely encouraging in terms of quantity and
quality of HVS data that can be exploited to constrain both the Milky Way
potential and the GC properties.Comment: 17 pages, 18 figures, accepted for publication in MNRA
Guidance algorithms for a free-flying space robot
Robotics is a promising technology for assembly, servicing, and maintenance of platforms in space. Several aspects of planning and guidance for telesupervised and fully autonomous robotic servicers are investigated. Guidance algorithms for proximity operation of a free flyer are described. Numeric trajectory optimization is combined with artificial intelligence based obstacle avoidance. An initial algorithm and the results of its simulating platform servicing scenario are discussed. A second algorithm experiment is then proposed
- …