Laser-driven generation of high-quality ultra-relativistic positron beams

An ultra-relativistic electron beam propagating through a high-Z solid triggers an electromagnetic cascade, whereby a large number of high-energy photons and electron–positron pairs are produced mainly via the bremsstrahlung and Bethe–Heitler processes, respectively. These mechanisms are routinely used to generate positron beams in conventional accelerators such as the electron–positron collider (LEP). Here we show that the application of similar physical mechanisms to a laser-driven electron source allows for the generation of high-quality positron beams in a much more compact and cheaper configuration. We anticipate that the application of these results to the next generation of lasers might open the pathway for the realization of an all-optical high-energy electron–positron collider.

Detecting TeV γ-rays from GRBs with km3 neutrino telescopes

Observing TeV photons from GRBs can greatly enhance our understanding of their emission mechanisms. Under-sea/ice neutrino telescopes—such as ANTARES in the Mediterranean Sea or IceCube at the South Pole—can also operate as a γ-ray observatory by detecting downgoing muons from the electromagnetic cascade induced by the interaction of the photons with the Earth's atmosphere. Theoretical calculations of the number of detectable muons from single GRB events, located at different redshifts and zenith distances, have been performed. The attenuation by pair production of TeV photons with cosmic infrared background photons has also been included.

Waves in Poynting-flux dominated jets

High-energy emission from blazars is thought to arise in a relativistic jet launched by a supermassive black hole. The rapid variability of the emission suggests that structure of length scale smaller than the gravitational radius of the central black hole is imprinted on the jet as it is launched, and modulates the radiation released after it has been accelerated to high Lorentz factor. We describe a mechanism which can account for the acceleration of the jet, and for the rapid variability of the radiation, based on the propagation characteristics of nonlinear waves in charge-starved, polar jets. These exhibit a delayed acceleration phase, that kicks-in when the inertia associated with the wave currents becomes important. The time structure imprinted on the jet at launch modulates the photons produced by the accelerating jet provided that the electromagnetic cascade in the black-hole magnetosphere is not prolific.