Gamma flashes from relativistic electron-positron plasma droplets

Abstract

Ultra-intense lasers are expected to produce, in near future, relativistic electron-positron plasma droplets. Considering the local photon production rate in complete leading order in quantum electrodynamics (QED), we point out that these droplets are interesting sources of gamma ray flashes. . Electron-positron plasmas are also interesting for astrophysical scenario [10]. Temperatures of about T ∼ 10 MeV, in a laser-generated plasma, would open, furthermore, channels for muon or pion production [11]. While these channels are interesting for their own right (see [12] for another avenue for laser driven particle production), a hot e + e − γ plasma droplet, exploding after the creation process by the enormous thermodynamic pressure, is a source of γ radiation. Such short γ flashes may be of future use in ultra-fast spectroscopic investigations of various kind.In this note, we are going to present estimates of the photon spectrum emerging from a e + e − γ plasma droplet with temperatures in the 10 MeV range. In contrast to often employed particle-in-cell (PIC) simulations (see [3] for a study of the start-up phase of a similarly hot plasma), we base our considerations on results from QED thermo-field theory. The expansion dynamics is treated in a schematic way, as our emphasis is on the photon emission characteristics.The calculation of the local spontaneous photon emission rate from a QED (electron-positron) plasma has been outlined in [13] to complete leading order in elec- * Electronic address: musnhigolam.mustafa@saha.ac.in † Electronic address: b.kaempfer@fzd.de tromagnetic coupling α by including two-loop order. The result, at the heart of our note, may be presented aswhere n F (E γ ) = (exp(E γ /T ) + 1) −1 denotes the Fermi distribution, and the dynamically generated asymptotic mass squared of the electron is m 2 ∞ = 2m 2 th . The thermal mass squared is given by m 2 th = e 2 T 2 /8 with e 2 = 4πα (The considerations apply for T > m e ± which are different from the non-relativistic case where the relevant scales are given by the masses of plasma particles and the temperature [5].) E γ = u · k is a short hand notation for the Lorentz scalar product of the medium's four-velocity u(t, x) and the photon's four-momentum k. This rate includes 2 ↔ 2 processes from one loop [14], viz., Compton scattering and pair annihilation which generate the leading logarithmic contribution (first three terms in (1)). In addition, the rate also includes the inelastic processes [15] from two-loop like bremsstrahlung (fourth term) and offshell pair annihilation (fifth term) with the correct incorporation [13,16] of the Landau-Pomeranchuk-Migdal effect that limits the coherence length of the emitted radiation. A common feature of the latter two processes is that they have off-shell fermion next to the vertex where the photon is emitted, and the virtuality of the fermion becomes very small if the photon is emitted in forward direction. However, contrary to the one-loop diagrams, the singularity is linear instead of logarithmic, and ...

Relativistic Three-Body Recombination with the QED Vacuum

“…This offers prospects for laboratory studies on relativistic e + e − plasmas which are of relevance to various astrophysical phenomena such as gamma-ray bursts, supernova explosions, and the evolution of the early universe [9]. Meanwhile, theoreticians have started to explore (ultra-) relativistic e + e − plasmas with densities 10 30 cm −3 , analyzing the thermalization process [10], dynamical properties [11], and photo-emission spectra [12]. In particular it was shown that in these extremely dense environments higher-order QED processes and multi-particle correlation effects may be prominent.…”

Dynamics and Emission of Mildly Relativistic Plasma

“…We consider kinetic evolution of nonequilibrium optically thick plasma consisting at the moment t = 0 of electron-positron pairs with number density n = 10 30 cm −3 in the small region with radius R 0 = 200 cm and average particle energy 600 keV. Although such parameters are far from both laboratory conditions and the real GRB sources, we consider this choice of parameters important since it provides some new insights with respect to the traditional hydrodynamic description 15,33,34,13,35 . Figs.…”

“…Electron-positron plasmas in the laboratory experiments or in thunderstorms have low density and are consequently optically thin 13,14 . In contrast, in a GRB source pair plasma is dense and optically thick 4,15,16 .…”

Positronium in superintense high-frequency laser fields

“…The Ps atom thereby becomes a 'microcollider' in which laser-driven e − + e + collisions occur at small impact parameters; e.g., an infrared laser with wavelength λ = 1 mm, and intensity I = 5.5 × 10 22 W/cm 2 can provide the threshold energy to create a muon + antimuon pair [4,5]. Other ambitious prospects, fostered by attaining high densities, include Bose-Einstein condensation of Ps in pursuit of an annihilation gamma ray laser [6].…”