Prospects for radio detection of ultra-high energy cosmic rays and neutrinos

Abstract

The origin and nature of the highest energy cosmic ray events is currently the subject of intense investigation by giant air shower arrays and fluorescent detectors. These particles reach energies well beyond what can be achieved in ground-based particle accelerators and hence they are fundamental probes for particle physics as well as astrophysics. One of the main topics today focuses on the high energy end of the spectrum and the potential for the production of high-energy neutrinos. Above about 10 20 eV cosmic rays from extragalactic sources are expected to be severely attenuated by pion photoproduction interactions with photons of the cosmic microwave background. Investigating the shape of the cosmic ray spectrum near this predicted cut-off will be very important. In addition, a significant high-energy neutrino background is naturally expected as part of the pion decay chain which also contains much information.Because of the scarcity of these high-energy particles, larger and larger ground-based detectors have been built. The new generation of digital radio telescopes may play an important role in this, if properly designed. Radio detection of cosmic ray showers has a long history but was abandoned in the 1970's. Recent experimental developments together with sophisticated air shower simulations incorporating radio emission give a clearer understanding of the relationship between the air shower parameters and the radio signal, and have led to resurgence in its use. Observations of air showers by the SKA could, because of its large collecting area, contribute significantly to measuring the cosmic ray spectrum at the highest energies. Because of the large surface area of the moon, and the expected excellent angular resolution of the SKA, using the SKA to detect radio Cherenkov emission from neutrino-induced cascades in lunar regolith will be potentially the most important technique for investigating cosmic ray origin at energies above the photoproduction cut-off.

Flavor composition and energy spectrum of astrophysical neutrinos

“…The concept that is in the most advanced stage is a large volume (cubic Kilometer) ice or water Cherenkov detector, with photon detectors distributed inside the volume, as originally proposed by the Dumand group [40] and now in different stages of development at the South Pole [41,42], in the Baikal lake [43] and in the mediterranean sea [44,45,46]. Several other alternative techiques are also being developed [47], that includes radio [48,49], acoustic and air shower [50,51] detection methods.…”

Perspectives of high-energy neutrino astronomy

“…GZK neutrinos (see fig.1) have energy typically in the 10 18 -10 20 eV, and the predicted fluxes are so small that km 3 detectors can only be very marginal, and larger detector masses and new detection methods are in order. Several interesting ideas are being developed (for a review see [39]), these include acoustic [40], radio [41] and Air Shower [42,43] detection.…”

Transition radiation at radio frequencies from ultrahigh-energy neutrino-induced showers

“…However, there are only a few estimates in the literature of TR from cosmic ray showers -either crossing from atmospheric air to a denser medium (e.g. clouds [20] or ground [21]) or emerging from ground into air (a rough estimate is given in [22]). While the methods presented in this paper are of general application, we are mostly motivated by the study of TR emitted when a shower, originated by a UHE neutrino interaction below the Earth surface, escapes the ground into the atmosphere.…”