Ultrarelativistic Electron-positron Plasma Research Articles

Fluid model simulation of solitons in an ultra-relativistic electron–positron plasma

In this study, the fully nonlinear relativistic ideal two-fluid equations are numerically integrated to show how solitary wave pulses can arise from simple initial conditions when electromagnetic waves parallel to a constant magnetic field are considered in a degenerate electron–positron plasma. The formation and propagation of one-dimensional fast wave solitons and slower wave pulses are identified as being related to a sound mode and the Alfvén mode, respectively. While solitons in relativistic electron–positron and similar plasmas have been studied theoretically by many authors, apart from some particle simulations and stationary large-amplitude treatments, only small-amplitude studies resulting in Korteweg–de Vries and related model equations have been employed to illustrate the occurrence of such nonlinear structures. These results extend and complement earlier theoretical treatments and are especially relevant for astrophysical plasmas.

Dispersion relation of modulational instability for one-dimensional standing solitary waves in hot ultrarelativistic electron–positron plasmas

In this paper, the non-linear dispersion relation of the system for interactions between high intensity laser and hot relativistic electron–positron plasma is derived. We restrict the problem to the standing solitons in ultrarelativistic plasmas and apply the quasineutrality condition. The modulational instability growth rate for different values of plasma temperatures, velocities and wave numbers are illustrated numerically. It is shown that, by increasing the unperturbed plasma enthalpy, the modulational instability growth rate decreases for all the values of plasma fluid velocities. It is also found that the growth rate shows an increasing trend with plasma fluid velocity. Furthermore, the impact of wave amplitude on the modulational instability growth rate is investigated explicitly. The growth rate increases with wave number as well as wave amplitude.

Equilibration of the chiral asymmetry due to finite electron mass in electron-positron plasma

We calculate the rate of collisional decay of the axial charge in an ultrarelativistic electron-positron plasma, also known as the chirality flipping rate. We find that contrary to the existing estimates, the chirality flipping rate appears already in the first order in the fine-structure constant $\ensuremath{\alpha}$ and is therefore orders of magnitude greater than previously believed. The main channels for the rapid relaxation of the axial charge are the collinear emission of a weakly damped photon and the Compton scattering. The latter contributes to the $\mathcal{O}(\ensuremath{\alpha})$ result because of the infrared divergence in its cross section, which is regularized on the soft scale $\ensuremath{\sim}eT$ due to the thermal corrections. Our results are important for the description of the early Universe processes (such as leptogenesis or magnetogenesis) that affect differently left- and right-chiral fermions of the Standard Model, as discussed in more details in the companion Letter.

Large amplitude electromagnetic solitons in a fully relativistic magnetized electron-positron-pair plasma

Nonlinear propagation of purely stationary large amplitude electromagnetic (EM) solitary waves in a magnetized electron–positron (EP) plasma is studied using a fully relativistic two-fluid hydrodynamic model which accounts for physical regimes of both weakly relativistic (P≪nmc2) and ultrarelativistic (P≫nmc2) random thermal energies. Here, P is the thermal pressure, n the number density and m the mass of a particle, and c is the speed of light in vacuum. While both the sub-Alfvénic and super-Alfvénic solitons coexist in the weakly relativistic regime, the ultrarelativistic EP plasmas in contrast support only the sub-Alfvénic solitons. Different limits of the Mach numbers and soliton amplitudes are also examined in these two physical regimes.

Propagation and Generation of Electromagnetic Waves at Proton Gyrofrequencies in a Relativistic Electron–Positron Plasma. I. Low-Frequency Weakly Damped Electromagnetic Waves

We consider the dispersion characteristics of electromagnetic waves in a plasma with strong magnetic field and equal content of relativistic electrons and positrons, whose synchrotron radiation can be the source of optical radiation of a pulsar. It is shown that when a small fraction of nonrelativistic protons with a nonequilibrium distribution function is present in the plasma, an effective instability can develop at frequencies below the first harmonic of the relativistic gyrofrequency of electrons, namely, at the harmonics of the proton gyrofrequency. This instability leads to the excitation of the O- and X-mode electromagnetic waves, which can, in principle, be related with the observed pulsar radiation. In part I of this paper, we study dispersion characteristics of low-frequency electromagnetic waves (with frequencies below the relativistic gyrofrequency of electrons) in an ultrarelativistic electron–positron plasma with an isotropic momentum distribution function of the particles. Instabilities of the O- and X-mode waves and the conditions of escape of the radiation from the region of strong magnetic field into a rarefied isotropic plasma will be considered in paper II. The results can be used in the interpretation of known experimental data on the dynamic pulsar radiation spectra obtained with high temporal and frequency resolution.

Modulational behavior of electromagnetic waves in ultra-relativistic electron-positron plasmas

The dynamical properties of electromagnetic (EM) waves in ultra-relativistic electron-positron (EP) plasmas are analytically investigated on the basis of the nonlinear governing equations obtained from a kinetic way. It is shown that the EM wave envelope will collapse and be trapped into a localized region for the modulation interaction with low frequency density variation induced by ponderomotive force. The correlation between the localized strong wave field and the pulsar radio emission is discussed.

Magnetic field induced by strong transverse plasmons in ultra-relativistic electron-positron plasmas

Context. We investigated the generation of localized magnetic fields in an ultra-relativistic non-isothermal electron-positron plasma by strong electromagnetic plasmons. Aims. The results obtained can be used to explain the origin of small-scale magnetic fields in the internal shock region of gamma-ray bursts with ultra-relativistic electron positron plasmas. Methods. The generation of magnetic fields was investigated with kinetic Vlasov Maxwell equations. Results. The self-generated magnetic field will collapse for modulation instability, leading to spatially highly intermittent magnetic fluxes, whose characteristic scale is much larger than relativistic plasma skin depth, which in turn is conducive to the generation of the long-life small-scale magnetic fields in the internal shock region of gamma-ray bursts.

Kinetic description of the Langmuir solitons in ultra-relativistic electron-positron plasmas

The nonlinear interaction between the high frequency Langmuir wave and the low frequency density fluctuation in ultrarelativistic isothermal electron positron plasmas is investigated from kinetic Vlasov equation. One dimensional Langmuir solitons are obtained, the width of which is so large that it is not relevant to the coherent pulsar radio emission.

Nonlinear Behavior of Electromagnetic Waves in Ultra‐Relativistic Electron‐Positron Plasmas

AbstractA set of nonlinear equations which can self‐consistently describe the behavior of high frequency Electromagnetic (EM) waves in un‐magnetized, ultra‐relativistic electron‐positron (e‐p) plasmas is obtained on the basis of Vlasov‐Maxwell equations. Nonlinear wave‐wave, wave‐particle interactions lead to the coupling of high frequency EM waves with low frequency density perturbations which result from EM waves radiation pressure. The same as that in conventional electron‐ion (e‐i) plasmas, strong EM waves in e‐p plasmas will give rise to density depletion in which itself are trapped. But on the contrary to that in e‐i plasmas, there no longer exists electrostatic acoustic–like wave in e‐p plasmas due to the absence of mass difference. For linear polarized EM waves, a stationary EM soliton with a spiky structure will be formed. The possible relation of the localized field to pulsar radio pulse is discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Time-dependent pair cascades in magnetospheres of neutron stars - I. Dynamics of the polar cap cascade with no particle supply from the neutron star surface

I argue that the problem of electromagnetically driven electron-positron cascades in magnetospheres of neutron stars must be addressed starting from first principles. I describe a general numerical algorithm for doing self-consistent kinetic simulations of electron-positron cascades - wherein particle acceleration, pair creation and screening of the electric field are calculated simultaneously - and apply it to model the Ruderman and Sutherland cascade in one dimension. I find that pair creation is quite regular and quasi-periodic. In each cycle a blob of ultrarelativistic electron-positron plasma is generated, it propagates into the magnetosphere leaving a tail of less relativistic plasma behind, and the next discharge occurs when this mildly relativistic plasma leaves the polar cap. A short burst of pair formation is followed by a longer quiet phase when accelerating electric field is screened and no pairs are produced. Some of freshly injected electron-positrons pairs get trapped in plasma oscillations creating a population of low energy particles. The cascade easily adjusts to the current density required by the pulsar magnetosphere by reversing some of the low energy particles. Each discharge generates a strong coherent superluminal electrostatic wave, which may be relevant for the problem of pulsar radioemission.

Colloquium: Field theoretic description of ultrarelativistic electron-positron plasmas

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.

What can we learn from electromagnetic plasmas about the quark–gluon plasma?

Ultra-relativistic electromagnetic plasmas can be used for improving our understanding of the quark–gluon plasma. In the weakly coupled regime, both plasmas can be described by transport theoretical and quantum field theoretical methods leading to similar results for the plasma properties (dielectric tensor, dispersion relations, plasma frequency, Debye screening, transport coefficients, damping and particle production rates). In particular, future experiments with ultra-relativistic electron–positron plasmas in ultra-strong laser fields might open the possibility of testing these predictions, e.g. the existence of a new fermionic plasma wave (plasmino). In the strongly coupled regime, electromagnetic plasmas such as complex plasmas can be used as models or at least analogies for the quark–gluon plasma possibly produced in relativistic heavy-ion experiments. For example, pair correlation functions can be used to investigate the equation of state and cross section enhancement for parton scattering can be explained.

Ultrarelativistic electron-positron plasma

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.

Formation of the radio profile components of the Crab pulsar

The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron-positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of the so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and the low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside of the MP can be explained in terms of our model.

Physics of Interpulse Emission in Radio Pulsars

The magnetized induced Compton scattering off the particles of the ultrarelativistic electron-positron plasma of pulsar is considered. The main attention is paid to the transverse regime of the scattering, which holds in a moderately strong magnetic field. We specifically examine the problem of induced transverse scattering of the radio beam into the background, which takes place in the open field line tube of a pulsar. In this case, the radiation is predominantly scattered backward, and the scattered component may grow considerably. Based on this effect, we for the first time suggest a physical explanation of the interpulse emission observed in the profiles of some pulsars. Our model can naturally account for the peculiar spectral and polarization properties of the interpulses. Furthermore, it implies a specific connection of the interpulse to the main pulse, which may reveal itself in the consistent intensity fluctuations of the components at different timescales. Diverse observational manifestations of this connection, including the moding behavior of PSR B1822–09, the peculiar temporal and frequency structure of the giant interpulses in the Crab pulsar, and the intrinsic phase correspondence of the subpulse patterns in the main pulse and the interpulse of PSR B1702–19, are discussed in detail. It is also argued that the pulse-to-pulse fluctuations of the scattering efficiency may lead to strong variability of the interpulse, which is yet to be studied observationally. In particular, some pulsars may exhibit transient interpulses, i.e., the scattered component may be detectable only occasionally.

Kinetic theory for radiation interacting with sound waves in ultrarelativistic pair plasmas

A kinetic theory for radiation interacting with sound waves in an ultrarelativistic electron-positron plasma is developed. It is shown that the effect of a spatial spectral broadening of the electromagnetic pulse is to introduce a reduction of the growth rates for the decay and modulational instabilities. Such spectral broadening could be due to a finite pulse coherence length, or through the use of random phase filters, and would stabilize the propagation of electromagnetic pulses.

NEUTRINO SPIN RELAXATION IN MEDIUM WITH STOCHASTIC CHARACTERISTICS

The helicity evolution of a neutrino propagating in randomly moving and polarized matter is studied. The type of the neutrino interaction with background fermions is arbitrary. We derive the equation for the description of the averaged neutrino helicity evolution. In the particular case of a τ-neutrino interacting with ultrarelativistic electron–positron plasma, we obtain the expression for the neutrino helicity relaxation rate in the explicit form. We study the neutrino spin relaxation in the relativistic primordial plasma. Supposing that the conversion of left-handed neutrinos into right-handed ones is suppressed at the early stages of the Universe evolution, we get the upper limit on the τ-neutrino mass.

Ultrarelativistic Plasma Shell Collisions in γ‐Ray Burst Sources: Dimensional Effects on the Final Steady State Magnetic Field

Ultrarelativistic electron-positron plasma shell collisions as an integral part of generic γ-ray burst (GRB) fireball models are studied in the framework of self-consistent three-dimensional particle-in-cell simulations. We compare scenarios at moderately relativistic (γ0 10) and ultrarelativistic (γ0 100) energies that directly correspond to the regimes of internal and external shell collisions, respectively, in GRB synchrotron emission models. Simulated systems comprise 5 × 108 particles, applying a relativistic, fully electromagnetic, massively parallelized code. It is found that Weibel-generated, steady state magnetic equipartition ratios in external collisions reach up to B ~ 12%, exceeding the respective internal ratios by nearly a power of 10. Enhanced B yields can be explained theoretically by the effective reduction of dimensionality in the ultrarelativistic limit, i.e., the energy-dependent confinement of the three-dimensional Weibel instability within quasi-two-dimensional plasma shell slices.

An Emission Mechanism for Extragalactic Radio Jets

view Abstract Citations (4) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Emission Mechanism for Extragalactic Radio Jets Yoon, Peter H. ; Ziebell, L. F. Abstract The observed emissions of radio waves from extragalactic radio jets are customarily interpreted in terms of the incoherent synchrotron radiation produced by a nonthermal population of relativistic electrons (or positrons) gyrating in a magnetic field. Such an interpretation requires, by necessity, a mechanism (or mechanisms) to constantly reenergize the particles in directions transverse to the magnetic field in momentum space. This paper, on the other hand, presents a possible alternative mechanism for radiation emission that does not require transverse reacceleration, albeit the theory is only preliminary at this stage. The emission mechanism described in the present paper is an induced plasma process that results from a nonlinear coupling of the electrostatic beam mode with the transverse electromagnetic mode. The beam mode is excited when a stream of ultrarelativistic electron-positron pair plasma nonlinearly interacts with low-frequency intrinsic turbulence. The only source of free energy for the instability is the streaming motion of the pair plasma. Therefore, as opposed to the incoherent synchrotron model, this mechanism (if, indeed, it is operative) has an advantage of not having to rely on the concept of constant renenergization of particles in the transverse direction. Publication: The Astrophysical Journal Pub Date: March 1996 DOI: 10.1086/176916 Bibcode: 1996ApJ...459..529Y Keywords: ACCELERATION OF PARTICLES; GALAXIES: JETS; MAGNETOHYDRODYNAMICS: MHD; RADIATION MECHANISMS: NONTHERMAL full text sources ADS |

Propagation of electromagnetic waves in a rotating ultrarelativistic electron–positron plasma

The nonlinear evaluation of the electromagnetic waves under the condition of extreme rotation of the plasma is studied. Solitons are found to generate in the electron–positron plasma of a rotating neutron star. The behavior of the solitons and pulsar radiation is discussed.