543 research outputs found
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
The effect of initial conditions on the electromagnetic radiation generation in type III solar radio bursts
Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Physics of Plasmas 20, 062903 (2013) and may be found at .Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [D. Tsiklauri, Phys. Plasmas, 18, 052903 (2011)]. The numerical simulations were carried out using different density profiles and fast electron distribution functions. It is shown that electromagnetic L and R modes are excited by the transverse current, initially imposed on the system. In the course of the simulations no further interaction of the electron beam with the background plasma could be observed
Spin-Dependent Cyclotron Decay Rates in Strong Magnetic Fields
Cyclotron decay and absorption rates have been well studied in the
literature, focusing primarily on spectral, angular and polarization
dependence. Astrophysical applications usually do not require retention of
information on the electron spin state, and these are normally averaged in
obtaining the requisite rates. In magnetic fields, higher order quantum
processes such as Compton scattering become resonant at the cyclotron frequency
and its harmonics, with the resonances being formally divergent. Such
divergences are usually eliminated by accounting for the finite lifetimes of
excited Landau states. This practice requires the use of spin-dependent
cyclotron rates in order to obtain accurate determinations of process rates
very near cyclotronic resonances, the phase space domain most relevant for
certain applications to pulsar models. This paper develops previous results in
the literature to obtain compact analytic expressions for cyclotron decay
rates/widths in terms of a series of Legendre functions of the second kind;
these expressions can be expediently used in astrophysical models. The rates
are derived using two popular eigenstate formalisms, namely that due to Sokolov
and Ternov, and that due to Johnson and Lippmann. These constitute two sets of
eigenfunctions of the Dirac equation that diagonalize different operators, and
accordingly yield different spin-dependent cyclotron rates. This paper
illustrates the attractive Lorentz transformation characteristics of the
Sokolov and Ternov formulation, which is another reason why it is preferable
when electron spin information must be explicitly retained.Comment: 11 pages, 2 embedded figures, apjgalley format, To appear in The
Astrophysical Journal, Vol 630, September 1, 2005 issu
Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
We study the non-thermal emissions in a solar flare occurring on 2003 May 29
by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This
flare shows several typical behaviors of the HXR and microwave emissions: time
delay of microwave peaks relative to HXR peaks, loop-top microwave and
footpoint HXR sources, and a harder electron energy distribution inferred from
the microwave spectrum than from the HXR spectrum. In addition, we found that
the time profile of the spectral index of the higher-energy (\gsim 100 keV)
HXRs is similar to that of the microwaves, and is delayed from that of the
lower-energy (\lsim 100 keV) HXRs. We interpret these observations in terms
of an electron transport model called {\TPP}. We numerically solved the
spatially-homogeneous {\FP} equation to determine electron evolution in energy
and pitch-angle space. By comparing the behaviors of the HXR and microwave
emissions predicted by the model with the observations, we discuss the
pitch-angle distribution of the electrons injected into the flare site. We
found that the observed spectral variations can qualitatively be explained if
the injected electrons have a pitch-angle distribution concentrated
perpendicular to the magnetic field lines rather than isotropic distribution.Comment: 32 pages, 12 figures, accepted for publication in The Astronomical
Journa
Collisional damping rates for plasma waves
The distinction between the plasma dynamics dominated by collisional
transport versus collective processes has never been rigorously addressed until
recently. A recent paper [Yoon et al., Phys. Rev. E 93, 033203 (2016)]
formulates for the first time, a unified kinetic theory in which collective
processes and collisional dynamics are systematically incorporated from first
principles. One of the outcomes of such a formalism is the rigorous derivation
of collisional damping rates for Langmuir and ion-acoustic waves, which can be
contrasted to the heuristic customary approach. However, the results are given
only in formal mathematical expressions. The present Brief Communication
numerically evaluates the rigorous collisional damping rates by considering the
case of plasma particles with Maxwellian velocity distribution function so as
to assess the consequence of the rigorous formalism in a quantitative manner.
Comparison with the heuristic ("Spitzer") formula shows that the accurate
damping rates are much lower in magnitude than the conventional expression,
which implies that the traditional approach over-estimates the importance of
attenuation of plasma waves by collisional relaxation process. Such a finding
may have a wide applicability ranging from laboratory to space and
astrophysical plasmas.Comment: 5 pages, 2 figures; Published in Physics of Plasmas, volume/Issue
23/6. Publisher: AIP Publishing LLC. Date: Jun 1, 2016. URL:
http://aip.scitation.org/doi/10.1063/1.4953802 Rights managed by AIP
Publishing LL
First-order thermal correction to the quadratic response tensor and rate for second harmonic plasma emission
Three-wave interactions in plasmas are described, in the framework of kinetic
theory, by the quadratic response tensor (QRT). The cold-plasma QRT is a common
approximation for interactions between three fast waves. Here, the first-order
thermal correction (FOTC) to the cold-plasma QRT is derived for interactions
between three fast waves in a warm unmagnetized collisionless plasma, whose
particles have an arbitrary isotropic distribution function. The FOTC to the
cold-plasma QRT is shown to depend on the second moment of the distribution
function, the phase speeds of the waves, and the interaction geometry. Previous
calculations of the rate for second harmonic plasma emission (via Langmuir-wave
coalescence) assume the cold-plasma QRT. The FOTC to the cold-plasma QRT is
used here to calculate the FOTC to the second harmonic emission rate, and its
importance is assessed in various physical situations. The FOTC significantly
increases the rate when the ratio of the Langmuir phase speed to the electron
thermal speed is less than about 3.Comment: 11 pages, 2 figures, submitted to Physics of Plasma
A closed expression for the UV-divergent parts of one-loop tensor integrals in dimensional regularization
Starting from the general definition of a one-loop tensor N-point function,
we use its Feynman parametrization to calculate the UV-divergent part of an
arbitrary tensor coefficient in the framework of dimensional regularization. In
contrast to existing recursion schemes, we are able to present a general
analytic result in closed form that enables direct determination of the
UV-divergent part of any one-loop tensor N-point coefficient independent from
UV-divergent parts of other one-loop tensor N-point coefficients. Simplified
formulas and explicit expressions are presented for A-, B-, C-, D-, E-, and
F-functions.Comment: 19 pages (single column), the result of previous versions is further
evaluated leading to a closed analytic expression for the UV-divergent part
of an arbitrary one-loop tensor coefficient, title is modified accordingly, a
sign error in the appendix (C_{00000000}) has been corrected, a mathematica
notebook containing an implementation of the newly derived formula is
attache
Instabilities in neutrino-plasma density waves
One examines the interaction and possible resonances between supernova
neutrinos and electron plasma waves. The neutrino phase space distribution and
its boundary regions are analyzed in detail. It is shown that the boundary
regions are too wide to produce non-linear resonant effects. The growth or
damping rates induced by neutrinos are always proportional to the neutrino flux
and .Comment: 9 pages, a few words modified to match PRD publicatio
Proton Cyclotron Features in Thermal Spectra of Ultra-magnetized Neutron Stars
A great deal of interest has been recently raised in connection with the
possibility that soft -ray repeaters (SGRs) and anomalous X-ray pulsars
(AXPs) contain {\em magnetars}, young neutron stars endowed with magnetic
fields G. In this paper we calculate thermal spectra from
ultra-magnetized neutron stars for values of the luminosity and magnetic field
believed to be relevant to SGRs and AXPs. Emergent spectra are found to be very
close to a blackbody at the star effective temperature and exhibit a
distinctive absorption feature at the proton cyclotron energy keV. The proton cyclotron features (PCFs) are
conspicuous (equivalent width of up to many hundreds eV) and relatively broad
(). The detection of the PCFs is well within the
capabilities of present X-ray spectrometers, like the HETGS and METGS on board
Chandra. Their observation might provide decisive evidence in favor of the
existence of magnetars.Comment: 7 pages, 4 figures, minor changes included, typos corrected. Accepted
for publication in Ap
Magnetic Photon Splitting: the S-Matrix Formulation in the Landau Representation
Calculations of reaction rates for the third-order QED process of photon
splitting in strong magnetic fields traditionally have employed either the
effective Lagrangian method or variants of Schwinger's proper-time technique.
Recently, Mentzel, Berg and Wunner (1994) presented an alternative derivation
via an S-matrix formulation in the Landau representation. Advantages of such a
formulation include the ability to compute rates near pair resonances above
pair threshold. This paper presents new developments of the Landau
representation formalism as applied to photon splitting, providing significant
advances beyond the work of Mentzel et al. by summing over the spin quantum
numbers of the electron propagators, and analytically integrating over the
component of momentum of the intermediate states that is parallel to field. The
ensuing tractable expressions for the scattering amplitudes are satisfyingly
compact, and of an appearance familiar to S-matrix theory applications. Such
developments can facilitate numerical computations of splitting considerably
both below and above pair threshold. Specializations to two regimes of interest
are obtained, namely the limit of highly supercritical fields and the domain
where photon energies are far inferior to that for the threshold of
single-photon pair creation. In particular, for the first time the
low-frequency amplitudes are simply expressed in terms of the Gamma function,
its integral and its derivatives. In addition, the equivalence of the
asymptotic forms in these two domains to extant results from effective
Lagrangian/proper-time formulations is demonstrated.Comment: 19 pages, 3 figures, REVTeX; accepted for publication in Phys. Rev.
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