Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. ?? 2013 Elsevier B.V. All rights reserved

The Giant Radio Array for Neutrino Detection (GRAND) 1 is a planned large-scale observatory of ultra-highenergy (UHE) cosmic particles -cosmic rays, gamma rays, and neutrinos with energies exceeding 10 8 GeV. Its ultimate goal is to solve the long-standing mystery of the origin of UHE cosmic rays. It will do so by detecting an unprecedented number of UHECRs and by looking with unmatched sensitivity for the undiscovered UHE neutrinos and gamma rays associated to them. Three key features of GRAND will make this possible: its large exposure at ultra-high energies, sub-degree angular resolution, and sensitivity to the unique signals made by UHE neutrinos.The strategy of GRAND is to detect the radio emission coming from large particle showers that develop in the terrestrial atmosphereextensive air showers -as a result of the interaction of UHE cosmic rays, gamma, rays, and neutrinos. To achieve this, GRAND will be the largest array of radio antennas ever built. The relative affordability of radio antennas makes the scale of construction possible. GRAND will build on years of progress in the field of radio-detection and apply the large body of technological, theoretical, and numerical advances, for the first time, to the radio-detection of air showers initiated by UHE neutrinos.The design of GRAND will be modular, consisting of several independent sub-arrays, each of 10 000 radio antennas deployed over 10 000 km 2 in radio-quiet locations. A staged construction plan ensures that key techniques are progressively validated, while simultaneously achieving important science goals in UHECR physics, radioastronomy, and cosmology early during construction.Already by 2025, using the first sub-array of 10 000 antennas, GRAND could discover the long-sought cosmogenic neutrinos -produced by interactions of ultra-high-energy cosmic-rays with cosmic photon fields -if their flux is as high as presently allowed, by reaching a sensitivity comparable to planned upgraded versions of existing experiments. By the 2030s, in its final configuration of 20 sub-arrays, GRAND will reach an unparalleled sensitivity to cosmogenic neutrino fluxes of 4 • 10 −10 GeV cm −2 s −1 sr −1 within 3 years of operation, which will guarantee their detection even if their flux is tiny. Because of its sub-degree angular resolution, GRAND will also search for point sources of UHE neutrinos, steady and transient, potentially starting UHE neutrino astronomy. Because of its access to ultra-high energies, GRAND will chart fundamental neutrino physics at these energies for the first time.GRAND will also be the largest detector of UHE cosmic rays and gamma rays. It will improve UHECR statistics at the highest energies ten-fold within a few years, and either discover UHE gamma rays or improve their limits ten-fold. Further, it will be a valuable tool in radioastronomy and cosmology, allowing for the discovery and follow-up of large numbers of radio transients -fast radio bursts, giant radio pulses -and for precise studies of the epoch of reionization.Following the disc...