28,519 research outputs found
The influence of the mass-ratio on the acceleration of particles by filamentation instabilities
Almost all sources of high energy particles and photons are associated with
jet phenomena. Prominent sources of such highly relativistic outflows are
pulsar winds and Active Galactic Nuclei. The current understanding of these
jets assumes diluted plasmas which are best described as kinetic phenomena. In
this kinetic description particle acceleration to ultra-relativistic speeds can
occur in completely unmagnetized and neutral plasmas through insetting effects
of instabilities. Even though the morphology and nature of particle spectra are
understood to a certain extent, the composition of the jets is not known yet.
While Poynting-flux dominated jets are certainly composed of electron-positron
plasmas, the understanding of the governing physics in AGN jets is mostly
unclear. In this article we investigate how the constituting elements of an
electron-positron-proton plasma behave differently under the variation of the
fundamental mass-ratio m_p/m_e. We studied initially unmagnetized
counterstreaming plasmas using fully relativistic three-dimensional
particle-in-cell simulations to investigate the influence of the mass-ratio on
particle acceleration and magnetic field generation in electron-positron-proton
plasmas. We covered a range of mass-ratios m_p/m_e between 1 and 100 with a
particle number composition of n_{p^+}/n_{e^+} of 1 in one stream, only protons
are injected in the other, whereas electrons are present in both to guarantee
charge neutrality in the simulation box. We find that with increasing proton
mass the instability takes longer to develop and for mass-ratios > 20 the
particles seem to be accelerated in two phases which can be accounted to the
individual instabilities of the different species. This means that for high
mass ratios the coupling between electrons/positrons and the heavier protons,
which occurs in low mass-ratios, disappears.Comment: 15 pages, 6 figure
Asymptotic Expansion of the One-Loop Approximation of the Chern-Simons Integral in an Abstract Wiener Space Setting
In an abstract Wiener space setting, we constract a rigorous mathematical
model of the one-loop approximation of the perturbative Chern-Simons integral,
and derive its explicit asymptotic expansion for stochastic Wilson lines.Comment: 39 page
Weibel instability and associated strong fields in a fully 3D simulation of a relativistic shock
Plasma instabilities (e.g., Buneman, Weibel and other two-stream
instabilities) excited in collisionless shocks are responsible for particle
(electron, positron, and ion) acceleration. Using a new 3-D relativistic
particle-in-cell code, we have investigated the particle acceleration and shock
structure associated with an unmagnetized relativistic electron-positron jet
propagating into an unmagnetized electron-positron plasma. The simulation has
been performed using a long simulation system in order to study the nonlinear
stages of the Weibel instability, the particle acceleration mechanism, and the
shock structure. Cold jet electrons are thermalized and slowed while the
ambient electrons are swept up to create a partially developed hydrodynamic
(HD) like shock structure. In the leading shock, electron density increases by
a factor of 3.5 in the simulation frame. Strong electromagnetic fields are
generated in the trailing shock and provide an emission site. We discuss the
possible implication of our simulation results within the AGN and GRB context.Comment: 4 pages, 3 figures, ApJ Letters, in pres
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