38,937 research outputs found
SIMLA: Simulating laser-particle interactions via classical and quantum electrodynamics
We present the Fortran code SIMLA, which is designed for the study of charged
particle dynamics in laser and other background fields. This can be done
classically via the Landau-Lifshitz equation, or alternatively, via the
simulation of photon emission events determined by strong-field
quantum-electrodynamics amplitudes and implemented using Monte-Carlo type
routines. Multiple laser fields can be included in the simulation and the
propagation direction, beam shape (plane wave, focussed paraxial, constant
crossed, or constant magnetic), and time envelope of each can be independently
specified.Comment: Submitted to Comp. Phys. Comm. The associated computer program and
corresponding manual will be made available on the CPC librar
Transverse spreading of electrons in high-intensity laser fields
We show that for collisions of electrons with a high-intensity laser,
discrete photon emissions introduce a transverse beam spread which is distinct
from that due to classical (or beam shape) effects. Via numerical simulations,
we show that this quantum induced transverse momentum gain of the electron is
manifest in collisions with a realistic laser pulse of intensity within reach
of current technology, and we propose it as a measurable signature of
strong-field quantum electrodynamics.Comment: 5 pages, 3 figures. Accepted for publication in Physical Review
Letter
A sub-regional management framework for South Pacific longline fisheries
The principal objective of this study was to determine if additional net benefits can be derived from the sub-regional longline fishery by the introduction of a new management agreement that would centre on the provision of licensing arrangements that would allow access by eligible
longline vessels to multiple Exclusive Economic Zones, i.e. Multi-zone Access. [90pp.
Anisotropic higher derivative gravity and inflationary universe
Stability analysis of the Kantowski-Sachs type universe in pure higher
derivative gravity theory is studied in details. The non-redundant generalized
Friedmann equation of the system is derived by introducing a reduced one
dimensional generalized KS type action. This method greatly reduces the labor
in deriving field equations of any complicate models. Existence and stability
of inflationary solution in the presence of higher derivative terms are also
studied in details. Implications to the choice of physical theories are
discussed in details in this paper.Comment: 9 page
Potential applications of digital, visible, and infrared data from geostationary environmental satellites
An hourly, digital data base from the Visible/Infrared Spin-Scan Radiometer (VISSR) instrument on the GOES-1 and SMS-2 geostationary satellites is described. Several examples of developmental applications of these quantitative digital data are presented. These include a review of recent attempts to develop products that are of use to meteorologists who provide services to aviation, agriculture, forestry, hydrology, oceanography, and climatology. The sample products include high resolution thermal gradients of land and ocean surfaces, thermal change analyses, fruit frost/freeze application, cloud-top altitude analysis, analysis of hurricane characteristics, and analyses of solar insolation
D-Brane Interactions in a Gravitational Shock Wave Background
We study D-branes in the background of a gravitational shock wave. We
consider the case of parallel D-branes located on opposite sides with respect
to the shock wave. Their interaction is studied by evaluating the cylinder
diagram using the boundary states technique. Boundary states are defined at
each D-brane and their scalar product is evaluated after propagation through
the shock wave. Taking the limit where the gravitational shock wave vanishes we
show that the amplitude evaluated is consistent with the flat space-time
result.Comment: To be published in Modern Physics Letters A, revised version with
references added, 12 page
The anomaly-free quantization of two-dimensional relativistic string. I
An anomaly-free quantum theory of a relativistic string is constructed in
two-dimensional space-time. The states of the string are found to be similar to
the states of a massless chiral quantum particle. This result is obtained by
generalizing the concept of an ``operator'' in quantum field theory.Comment: LaTeX, 19 pages, no figure
Probing the mass function of halo dark matter via microlensing
The simplest interpretation of the microlensing events observed towards the
Large Magellanic Clouds is that approximately half of the mass of the Milky Way
halo is in the form of MAssive Compact Halo Objects with . It is not possible, due to limits from star counts and chemical
abundance arguments, for faint stars or white dwarves to comprise such a large
fraction of the halo mass. This leads to the consideration of more exotic lens
candidates, such as primordial black holes, or alternative lens locations. If
the lenses are located in the halo of the Milky Way, then constraining their
mass function will shed light on their nature. Using the current microlensing
data we find, for four halo models, the best fit parameters for delta-function,
primordial black hole and various power law mass functions. The best fit
primordial black hole mass functions, despite having significant finite width,
have likelihoods which are similar to, and for one particular halo model
greater than, those of the best fit delta functions . We then use Monte Carlo
simulations to investigate the number of microlensing events necessary to
determine whether the MACHO mass function has significant finite width. If the
correct halo model is known, then 500 microlensing events will be
sufficient, and will also allow determination of the mass function parameters
to .Comment: 28 pages including 14 figures, version to appear in ApJ, minor
changes to discussio
The Theory of a Quantum Noncanonical Field in Curved Spacetimes
Much attention has been recently devoted to the possibility that quantum
gravity effects could lead to departures from Special Relativity in the form of
a deformed Poincar\`e algebra. These proposals go generically under the name of
Doubly or Deformed Special Relativity (DSR). In this article we further explore
a recently proposed class of quantum field theories, involving noncanonically
commuting complex scalar fields, which have been shown to entail a DSR-like
symmetry. An open issue for such theories is whether the DSR-like symmetry has
to be taken as a physically relevant symmetry, or if in fact the "true"
symmetries of the theory are just rotations and translations while boost
invariance has to be considered broken. We analyze here this issue by extending
the known results to curved spacetime under both of the previous assumptions.
We show that if the symmetry of the free theory is taken to be a DSR-like
realization of the Poincar\'e symmetry, then it is not possible to render such
a symmetry a gauge symmetry of the curved physical spacetime. However, it is
possible to introduce an auxiliary spacetime which allows to describe the
theory as a standard quantum field theory in curved spacetime. Alternatively,
taking the point of view that the noncanonical commutation of the fields
actually implies a breakdown of boost invariance, the physical spacetime
manifold has to be foliated in surfaces of simultaneity and the field theory
can be coupled to gravity by making use of the ADM prescription.Comment: 9 pages, no figure
Coulomb screening in mesoscopic noise: a kinetic approach
Coulomb screening, together with degeneracy, is characteristic of the
metallic electron gas. While there is little trace of its effects in transport
and noise in the bulk, at mesoscopic scales the electronic fluctuations start
to show appreciable Coulomb correlations. Within a strictly standard Boltzmann
and Fermi-liquid framework, we analyze these phenomena and their relation to
the mesoscopic fluctuation-dissipation theorem, which we prove. We identify two
distinct screening mechanisms for mesoscopic fluctuations. One is the
self-consistent response of the contact potential in a non-uniform system. The
other couples to scattering, and is an exclusively non-equilibrium process.
Contact-potential effects renormalize all thermal fluctuations, at all scales.
Collisional effects are relatively short-ranged and modify non-equilibrium
noise. We discuss ways to detect these differences experimentally.Comment: Source: REVTEX. 16 pp.; 7 Postscript figs. Accepted for publication
in J. Phys.: Cond. Ma
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