16,077 research outputs found
From electrons to Janskys: Full stokes polarized radiative transfer in 3D relativistic particle-in-cell jet simulations
The underlying plasma composition of relativistic extragalactic jets remains
largely unknown. Relativistic magnetohydrodynamic (RMHD) models are able to
reproduce many of the observed macroscopic features of these outflows. The
nonthermal synchrotron emission detected by very long baseline interferometric
(VLBI) arrays, however, is a by-product of the kinetic-scale physics occurring
within the jet, physics that is not modeled directly in most RMHD codes. This
paper attempts to discern the radiative differences between distinct plasma
compositions within relativistic jets using small-scale 3D relativistic
particle-in-cell (PIC) simulations. We generate full Stokes imaging of two PIC
jet simulations, one in which the jet is composed of an electron-proton
(-) plasma (i.e., a normal plasma jet), and the other in which
the jet is composed of an electron-positron (-) plasma (i.e., a
pair plasma jet). We examined the differences in the morphology and intensity
of the linear polarization (LP) and circular polarization (CP) emanating from
these two jet simulations. We find that the fractional level of CP emanating
from the - plasma jet is orders of magnitude larger than the
level emanating from an - plasma jet of a similar speed and
magnetic field strength. In addition, we find that the morphology of both the
linearly and circularly polarized synchrotron emission is distinct between the
two jet compositions. We also demonstrate the importance of slow-light
interpolation and we highlight the effect that a finite light-crossing time has
on the resultant polarization when ray-tracing through relativistic plasma.Comment: 21 pages, 13 figures; accepted for publication in A&
Electromagnetic field near cosmic string
The retarded Green function of the electromagnetic field in spacetime of a
straight thin cosmic string is found. It splits into a geodesic part
(corresponding to the propagation along null rays) and to the field scattered
on the string. With help of the Green function the electric and magnetic fields
of simple sources are constructed. It is shown that these sources are
influenced by the cosmic string through a self-interaction with their field.
The distant field of static sources is studied and it is found that it has a
different multipole structure than in Minkowski spacetime. On the other hand,
the string suppresses the electric and magnetic field of distant sources--the
field is expelled from regions near the string.Comment: 12 pages, 8 figures (low-resolution figures; for the version with
high-resolution figures see http://utf.mff.cuni.cz/~krtous/papers/), v2: two
references added, typos correcte
Non-equilibrium Entanglement and Noise in Coupled Qubits
We study charge entanglement in two Coulomb-coupled double quantum dots in
thermal equilibrium and under stationary non-equilibrium transport conditions.
In the transport regime, the entanglement exhibits a clear switching threshold
and various limits due to suppression of tunneling by Quantum Zeno localisation
or by an interaction induced energy gap. We also calculate quantum noise
spectra and discuss the inter-dot current correlation as an indicator of the
entanglement in transport experiments.Comment: 4 pages, 4 figure
Exact results for interacting electrons in high Landau levels
We study a two-dimensional electron system in a magnetic field with a fermion
hardcore interaction and without disorder. Projecting the Hamiltonian onto the
n-th Landau level, we show that the Hartree-Fock theory is exact in the limit n
\rightarrow \infty, for the high temperature, uniform density phase of an
infinite system; for a finite-size system, it is exact at all temperatures. In
addition, we show that a charge-density wave arises below a transition
temperature T_t. Using Landau theory, we construct a phase diagram which
contains both unidirectional and triangular charge-density wave phases. We
discuss the unidirectional charge-density wave at zero temperature and argue
that quantum fluctuations are unimportant in the large-n limit. Finally, we
discuss the accuracy of the Hartree-Fock approximation for potentials with a
nonzero range such as the Coulomb interaction.Comment: RevTex, 12 pages with figures included in same file; to appear in
Physical Review
Measuring the condensate fraction of rapidly rotating trapped boson systems: off-diagonal order from the density
We demonstrate a direct connection between the density profile of a system of
ultra-cold trapped bosonic particles in the rapid-rotation limit and its
condensate fraction. This connection can be used to probe the crossover from
condensed vortex-lattice states to uncondensed quantum fluid states that occurs
in rapidly rotating boson systems as the particle density decreases or the
rotation frequency increases. We illustrate our proposal with a series of
examples, including ones based on models of realistic finite trap systems, and
comment on its application to freely expanding boson density profile
measurements.Comment: 4 pages, 3 figures, version accepted for publication in Phys. Rev.
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