Ultrarelativistic Velocities Research Articles

Constraints on string networks with junctions

We consider the constraints on string networks with junctions in which the strings may all be different, as may be found, for example, in a network of $(p,q)$ cosmic superstrings. We concentrate on three aspects of junction dynamics. First we consider the propagation of small-amplitude waves across a static three-string junction. Then, generalizing our earlier work, we determine the kinematic constraints on two colliding strings with different tensions. As before, the important conclusion is that strings do not always reconnect with a third string; they can pass straight through one another (or in the case of non-Abelian strings become stuck in an X configuration), the constraint depending on the angle at which the strings meet, on their relative velocity, and on the ratios of the string tensions. For example, if the two colliding strings have equal tensions, then for ultrarelativistic initial velocities they pass through one another. However, if their tensions are sufficiently different they can reconnect. Finally, we consider the global properties of junctions and strings in a network. Assuming that, in a network, the incoming waves at a junction are independently randomly distributed, we determine the root-mean-square (r.m.s.) velocities of strings and calculate the average speed at which a junction moves along each of the three strings from which it is formed. Our findings suggest that junction dynamics may be such as to preferentially remove the heavy strings from the network leaving a network of predominantly light strings. Furthermore the r.m.s. velocity of strings in a network with junctions is smaller than $1/\sqrt{2}$, the result for conventional Nambu-Goto strings without junctions in Minkowski space-time.

Relativistic unsteady Petschek-type model of magnetic reconnection

A model of time-dependent Petschek-type reconnection of arbitrary strong magnetic fields is presented where all necessary relativistic effects are taken into account. Reconnection is supposed to be initiated due to a local decrease of the plasma conductivity inside the diffusion region, which results in the appearance of an electric field along the X-line. This electric field is considered as a given arbitrary function of time. Then all MHD parameters as well as the shape of the moving Petschek-type shocks are obtained from the ideal relativistic MHD equations written in terms of 4-magnetic field and 4-velocity vectors as suggested by Lichnerowicz. The analysis is restricted to a symmetric current sheet geometry and to the case of weak reconnection, where the reconnection rate is supposed to be a small parameter. The solution obtained extends the well-known Petschek model for the steady-state case to incorporate relativistic effects of impulsive reconnection. It is shown that the plasma is accelerated at the slow shocks to ultrarelativistic velocities with high Lorentz-factors only for current layers embedded into strong magnetic fields and low-beta plasmas. In this case the plasma is strongly compressed and heated while the normal size of the outflow region with the accelerated plasma becomes very small.

Ionization of light atoms by ultra-fast ions

We propose a semi-relativistic symmetric eikonal distorted wave method (SRSE) for treating collisions of fast and ultra-fast projectiles with light and medium-heavy atomic targets. The projectile interaction with target electrons is described by the Liénard–Wiechert (LW) potential, within the impact parameter approach. Our model allows to estimate two-centre effects in fast heavy-particle collisions and analyse the limit of the ultra-relativistic collisions. We show that the improvement upon the first Born approximation (FBA) by taking into account the exact boundary conditions in the entrance and exit channels eliminates the well-known anomaly of the FBA ionization cross section at ultra-relativistic impact velocities.

Compression and acceleration of dense electron bunches by ultraintense laser pulses with sharp rising edge

In this paper, the generation of a single ultrashort and coherent relativistic electron bunch (relativistic electron mirror) during interaction of an ultraintense femtosecond laser pulse having a sharp enough rising edge (nonadiabatic laser pulse) with a thin plasma layer is considered. It is shown that due to the action of the radiation reaction forces the Coulomb repulsion among the bunch electrons is partially compensated and the initial geometry of the bunch is supported in the acceleration process. Besides, the bunch can be compressed by many times in the longitudinal direction at the initial stage of interaction with the front of the nonadiabatic laser pulse. As a result, all of the bunch electrons can be synchronously accelerated to ultrarelativistic velocities during the first several half periods of the external electromagnetic field that can correspond to time intervals of hundreds of femtoseconds in the laboratory frame. The characteristics of the accelerated electron bunches for different laser-plasma parameters (shape of laser pulse, initial density of electrons in the target, and initial target thickness) are investigated. One possible application for relativistic electron mirrors is considered. It is shown that the reflection of a probe counter-propagating laser pulse from such a mirror can produce intense, ultrashort, and coherent hard x-ray pulse. The spectrum of the frequency up-shifted radiation is investigated.

Gravitational waves in magnetized relativistic plasmas

We study the propagation of gravitational waves (GW's) in a uniformly magnetized plasma at arbitrary angles to the magnetic field. No a priori assumptions are made about the temperature, and we consider both a plasma at rest and a plasma flowing out at ultrarelativistic velocities. In the $3+1$ orthonormal tetrad description, we find that all three fundamental low-frequency plasma wave modes are excited by the GW's. Alfv\'en waves are excited by a \ifmmode\times\else\texttimes\fi{} polarized GW, whereas the slow and fast magnetoacoustic modes couple to the + polarization. The slow mode, however, does not interact coherently with the GW. The most relevant wave mode is the fast magnetoacoustic mode which in a strongly magnetized plasma has a vanishingly small phase lag with respect to the GW allowing for coherent interaction over large length scales. When the background magnetic field is almost, but not entirely, parallel to the GW's direction of propagation even the Alfv\'en waves grow to first order in the GW amplitude. Finally, we calculate the growth of the magnetoacoustic waves and the damping of the GW.

Gravitational ultrarelativistic interaction of classical particles in the context of unification of interactions

The response of the ultrarelativistic particle with spin in a Schwarzschild field to the gravitomagnetic components as measured by the comoving observer is investigated. The dependence of the particle's spin–orbit acceleration on the Lorentz γ-factor and the spin orientation is studied. The concrete circular ultrarelativistic orbit of radius r = 3m is considered as a partial solution of the Mathisson–Papapetrou equations and as the corresponding high-energy quantum state of the Dirac particle. Numerical estimates for protons and electrons near black holes are given. A tendency of gravitational and electromagnetic interactions to approach in quantitative terms at ultrarelativistic velocities is discussed.

Radiation of a Charge Moving Uniformly in a Nonstationary Medium with x-1 Depending on Time as sech2(t)

The radiation of a charge moving uniformly in a homogeneous medium with the permittivity time dependence typical of the Epstein symmetric layer is studied. Special cases of small amplitudes of the permittivity variation and ultrarelativistic charge velocities are considered.

Ultrarelativistic envelope solitons in a magnetized electron-positron plasma.

The nonlinear propagation of intense electromagnetic radiation in a pulsar magnetosphere is investigated. The radiation is considered to be a circularly polarized electromagnetic wave, in whose field electrons and positrons acquire ultrarelativistic velocities. The nonlinear frequency shift due to the wave-plasma interaction is found to cause the wave localization, and it produces a new kind of envelope soliton, which in coupling with the ambient magnetic field generates intense ambipolar field along the magnetic lines.

Phenomenological formulation of direct interparticle interaction in relativistic theory of gravitation

The general equations of relativistic dynamics of point masses in the post-Newtonian approximation and in the approximation of ultrarelativistic velocities are considered. The consequences of the weak principle of equivalence and its relation with the hypothesis of geodesics is studied. It is shown that, in the above approximations, the equations of motion reduce to the equations of Riemann geodesics.

The Stability of a Magnetized Electron Plasma in the Field of a Circularly Polarized Electromagnetic Wave

The dispersion relation is derived and analyzed for a magnetized electron plasma in the field of a powerful circularly polarized homogeneous pump wave propogating along the constant magnetic field. It is shown that decay instabilities appear for a weak pump while a strong pump, in which the electrons reach ultrarelativistic velocities, leads to aperiodic instabilities.

Relativistic Stellar-Wind Torques

view Abstract Citations (403) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relativistic Stellar-Wind Torques Michel, F. C. Abstract Several authors have calculated the torque on the Sun owing to the solar wind. We extend those treat- ments to encompass both special- and geneial-relativistic effects. A direct parallel treatment is feasible, and the major correction is, as would be expected, from the increased effective mass density of a rela- tivistic fluid. The treatment may be extended approximately to the limit of zero mass loss, wherein the toi que is entirely from the electromagnetic energy radiated by the rotating magnetic moment of the star. Application to rotational models of pulsars is illustrated with the conclusion that NP 0532, for ex- ample, would have a magiietic moment of order 3 X 1tY~ gauss cm3 (within certain assumptions regard- ing the rate of mass loss). Centrifugal forces are capable of accelerating the plasma to ultrarelativistic velocities, even in the magnetohydrodynamic approximation. The existence of pulsars therefore suggests a new and highly efficient source of relativistic particles Publication: The Astrophysical Journal Pub Date: November 1969 DOI: 10.1086/150233 Bibcode: 1969ApJ...158..727M full text sources ADS |