108 research outputs found
Surface modes and multi-power law structure in the early-time response of magnetic targets
It was recently demonstrated [P. B. Weichman, Phys. Rev. Lett. {\bf 91},
143908 (2003)] that the scattered electric field from highly conducting targets
following a rapidly terminated electromagnetic pulse displays a universal
power law divergence at early time. It is now shown that for
strongly permeable targets, , where is the
background magnetic permeability, the early time regime separates into two
distinct power law regimes, with the early-early time behavior
crossing over to at late-early time, reflecting a spectrum of
magnetic surface modes. The latter is confirmed by data from ferrous targets
where , and for which the early-early time regime
is invisibly narrow.Comment: 4 pages, 3 figure
Phase Control of Nonlinear Breit-Wheeler Pair Creation
Electron-positron pair creation occurs throughout the universe in the
environments of extreme astrophysical objects, such as pulsar magnetospheres
and black hole accretion disks. The difficulty of emulating these environments
in the laboratory has motivated the use of ultrahigh-intensity laser pulses for
pair creation. Here we show that the phase offset between a laser pulse and its
second harmonic can be used to control the relative transverse motion of
electrons and positrons created in the nonlinear Breit-Wheeler process.
Analytic theory and particle-in-cell simulations of a head-on collision between
a two-color laser pulse and electron beam predict that with an appropriate
phase offset, the electrons will drift in one direction and the positrons in
the other. The resulting current may provide a collective signature of
nonlinear Breit-Wheeler, while the spatial separation resulting from the
relative motion may facilitate isolation of positrons for subsequent
applications or detection.Comment: 8 pages, 5 figure
Criticality and Superfluidity in liquid He-4 under Nonequilibrium Conditions
We review a striking array of recent experiments, and their theoretical
interpretations, on the superfluid transition in He in the presence of a
heat flux, . We define and evaluate a new set of critical point exponents.
The statics and dynamics of the superfluid-normal interface are discussed, with
special attention to the role of gravity. If is in the same direction as
gravity, a self-organized state can arise, in which the entire sample has a
uniform reduced temperature, on either the normal or superfluid side of the
transition. Finally, we review recent theory and experiment regarding the heat
capacity at constant . The excitement that surrounds this field arises from
the fact that advanced thermometry and the future availability of a
microgravity experimental platform aboard the International Space Station will
soon open to experimental exploration decades of reduced temperature that were
previously inaccessible.Comment: 16 pages, 9 figures, plus harvard.sty style file for references
Accepted for publication in Colloquia section of Reviews of Modern Physic
Renormalization Group for Large N Strongly Commensurate Dirty Boson Model
The large N sigma model, in D<4 space-time dimensions, with disorder a
function of d space dimensions, is analyzed via a renormalization group
treatment. Critical exponents for average quantities are calculated, first to
lowest order and then to all orders, in . In particular, it
is found that . When D=d+1, this model is equivalent to a large N
limit of the strongly commensurate dirty boson problem.Comment: 16 pages, 4 figures, to be published in PR
Analytic pulse technique for computational electromagnetics
Numerical modeling of electromagnetic waves is an important tool for
understanding the interaction of light and matter, and lies at the core of
computational electromagnetics. Traditional approaches to injecting and
evolving electromagnetic waves, however, can be prohibitively expensive and
complex for emerging problems of interest and can restrict the comparisons that
can be made between simulation and theory. As an alternative, we demonstrate
that electromagnetic waves can be incorporated analytically by decomposing the
physics equations into analytic and computational parts. In particle-in-cell
simulation of laser--plasma interaction, for example, treating the laser pulse
analytically enables direct examination of the validity of approximate
solutions to Maxwell's equations including Laguerre--Gaussian beams, allows
lower-dimensional simulations to capture 3-D--like focusing, and facilitates
the modeling of novel space--time structured laser pulses such as the flying
focus. The flexibility and new routes to computational savings introduced by
this analytic pulse technique are expected to enable new simulation directions
and significantly reduce computational cost in existing areas.Comment: 26 pages, 9 figure
Coherence and superradiance from a plasma-based quasiparticle accelerator
Coherent light sources, such as free electron lasers, provide bright beams
for biology, chemistry, physics, and advanced technological applications.
Increasing the brightness of these sources requires progressively larger
devices, with the largest being several km long (e.g., LCLS). Can we reverse
this trend, and bring these sources to the many thousands of labs spanning
universities, hospitals, and industry? Here we address this long-standing
question by rethinking basic principles of radiation physics. At the core of
our work is the introduction of quasi-particle-based light sources that rely on
the collective and macroscopic motion of an ensemble of light-emitting charges
to evolve and radiate in ways that would be unphysical when considering single
charges. The underlying concept allows for temporal coherence and superradiance
in fundamentally new configurations, providing radiation with clear
experimental signatures and revolutionary properties. The underlying concept is
illustrated with plasma accelerators but extends well beyond this case, such as
to nonlinear optical configurations. The simplicity of the quasi-particle
approach makes it suitable for experimental demonstrations at existing laser
and accelerator facilities.Comment: 15 pages, 4 figure
Quantum critical phenomena of long-range interacting bosons in a time-dependent random potential
We study the superfluid-insulator transition of a particle-hole symmetric
system of long-range interacting bosons in a time-dependent random potential in
two dimensions, using the momentum-shell renormalization-group method. We find
a new stable fixed point with non-zero values of the parameters representing
the short- and long-range interactions and disorder when the interaction is
asymptotically logarithmic. This is contrasted to the non-random case with a
logarithmic interaction, where the transition is argued to be first-order, and
to the Coulomb interaction case, where either a first-order transition or
an XY-like transition is possible depending on the parameters. We propose that
our model may be relevant in studying the vortex liquid-vortex glass transition
of interacting vortex lines in point-disordered type-II superconductors.Comment: 10 pages, 3 figure
Infrared Behavior of Interacting Bosons at Zero Temperature
We exploit the symmetries associated with the stability of the superfluid
phase to solve the long-standing problem of interacting bosons in the presence
of a condensate at zero temperature. Implementation of these symmetries poses
strong conditions on the renormalizations that heal the singularities of
perturbation theory. The renormalized theory gives: For d>3 the Bogoliubov
quasiparticles as an exact result; for 1<d<=3 a nontrivial solution with the
exact exponent for the singular longitudinal correlation function, with phonons
again as low-lying excitations.Comment: Minor Changes. 4 pages, RevTeX, no figures, uses multicol.sty e-mail:
[email protected]
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