1,365 research outputs found
Dynamics of spin 1/2 quantum plasmas
The fully nonlinear governing equations for spin 1/2 quantum plasmas are
presented. Starting from the Pauli equation, the relevant plasma equations are
derived, and it is shown that nontrivial quantum spin couplings arise, enabling
studies of the combined collective and spin dynamics. The linear response of
the quantum plasma in an electron--ion system is obtained and analyzed.
Applications of the theory to solid state and astrophysical systems as well as
dusty plasmas are pointed out.Comment: 4 pages, 2 figures, to appear in Physical Review Letter
Electrodynamics of Magnetars III: Pair Creation Processes in an Ultrastrong Magnetic Field and Particle Heating in a Dynamic Magnetosphere
We consider the details of the QED processes that create electron-positron
pairs in magnetic fields approaching and exceeding 10^{14} G. The formation of
free and bound pairs is addressed, and the importance of positronium
dissociation by thermal X-rays is noted. We calculate the collision cross
section between an X-ray and a gamma ray, and point out a resonance in the
cross section when the gamma ray is close to the threshold for pair conversion.
We also discuss how the pair creation rate in the open-field circuit and the
outer magnetosphere can be strongly enhanced by instabilities near the light
cylinder. When the current has a strong fluctuating component, a cascade
develops. We examine the details of particle heating, and show that a high rate
of pair creation can be sustained close to the star, but only if the spin
period is shorter than several seconds. The dissipation rate in this turbulent
state can easily accommodate the observed radio output of the transient
radio-emitting magnetars, and even their infrared emission. Finally, we outline
how a very high rate of pair creation on the open magnetic field lines can help
to stabilize a static twist in the closed magnetosphere and to regulate the
loss of magnetic helicity by reconnection at the light cylinder.Comment: 25 pages, submitted to the Astrophysical Journa
Neutrino emission via the plasma process in a magnetized plasma
Neutrino emission via the plasma process using the vertex formalism for QED
in a strongly magnetized plasma is considered. A new vertex function is
introduced to include the axial vector part of the weak interaction. Our
results are compared with previous calculations, and the effect of the axial
vector coupling on neutrino emission is discussed. The contribution from the
axial vector coupling can be of the same order as or greater than the vector
vector coupling under certain plasma conditions.Comment: 20 pages, 3 figure
Optimized gyrosynchrotron algorithms and fast codes
Gyrosynchrotron (GS) emission of charged particles spiraling in magnetic
fields plays an exceptionally important role in astrophysics. In particular,
this mechanism makes a dominant contribution to the continuum solar and stellar
radio emissions. However, the available exact equations describing the emission
process are extremely slow computationally, thus limiting the diagnostic
capabilities of radio observations. In this work, we present approximate GS
codes capable of fast calculating the emission from anisotropic electron
distributions. The computation time is reduced by several orders of magnitude
compared with the exact formulae, while the computation error remains within a
few percent. The codes are implemented as the executable modules callable from
IDL; they are made available for users via web sites.Comment: Proceedings of the IAU Symposium 274 "Advances in Plasma
Astrophysics
Diffusive shock acceleration in extragalactic jets
We calculate the temporal evolution of distributions of relativistic
electrons subject to synchrotron and adiabatic processes and Fermi-like
acceleration in shocks. The shocks result from Kelvin-Helmholtz instabilities
in the jet. Shock formation and particle acceleration are treated in a
self-consistent way by means of a numerical hydrocode. We show that in our
model the number of relativistic particles is conserved during the evolution,
with no need of further injections of supra-thermal particles after the initial
one. From our calculations, we derive predictions for values and trends of
quantities like the spectral index and the cutoff frequency that can be
compared with observations.Comment: 12 pages containing 7 postscript figures; uses A&A macros. Accepted
for publication in Astronomy and Astrophysic
An alternative to the plasma emission model: Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts
1.5D PIC, relativistic, fully electromagnetic (EM) simulations are used to
model EM wave emission generation in the context of solar type III radio
bursts. The model studies generation of EM waves by a super-thermal, hot beam
of electrons injected into a plasma thread that contains uniform longitudinal
magnetic field and a parabolic density gradient. In effect, a single magnetic
line connecting Sun to earth is considered, for which several cases are
studied. (i) We find that the physical system without a beam is stable and only
low amplitude level EM drift waves (noise) are excited. (ii) The beam injection
direction is controlled by setting either longitudinal or oblique electron
initial drift speed, i.e. by setting the beam pitch angle. In the case of zero
pitch angle, the beam excites only electrostatic, standing waves, oscillating
at plasma frequency, in the beam injection spatial location, and only low level
EM drift wave noise is also generated. (iii) In the case of oblique beam pitch
angles, again electrostatic waves with same properties are excited. However,
now the beam also generates EM waves with the properties commensurate to type
III radio bursts. The latter is evidenced by the wavelet analysis of transverse
electric field component, which shows that as the beam moves to the regions of
lower density, frequency of the EM waves drops accordingly. (iv) When the
density gradient is removed, electron beam with an oblique pitch angle still
generates the EM radiation. However, in the latter case no frequency decrease
is seen. Within the limitations of the model, the study presents the first
attempt to produce simulated dynamical spectrum of type III radio bursts in
fully kinetic plasma model. The latter is based on 1.5D non-zero pitch angle
(non-gyrotropic) electron beam, that is an alternative to the plasma emission
classical mechanism.Comment: Physics of Plasmas, in press, May 2011 issue (final accepted version
Elliptic operators on manifolds with singularities and K-homology
It is well known that elliptic operators on a smooth compact manifold are
classified by K-homology. We prove that a similar classification is also valid
for manifolds with simplest singularities: isolated conical points and fibered
boundary. The main ingredients of the proof of these results are: an analog of
the Atiyah-Singer difference construction in the noncommutative case and an
analog of Poincare isomorphism in K-theory for our singular manifolds.
As applications we give a formula in topological terms for the obstruction to
Fredholm problems on manifolds with singularities and a formula for K-groups of
algebras of pseudodifferential operators.Comment: revised version; 25 pages; section with applications expande
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