Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

We are living exciting times: we are now able to probe the most violent events of the Universe with diverse messengers (cosmic rays, neutrinos, photons and gravitational waves). One challenge to complete the multi-messenger picture resides in the highest energies, as no ultra-high energy neutrinos, with energy > 10^17 eV, have been observed yet. This challenge could be undertaken by the GRAND (Giant Radio Array for Neutrino Detection) project. GRAND is a proposal for a large-scale array of self-triggered radio antennas. It stands out today as a unique experiment which plans to reach ambitious sensitivity and sub-degree angular resolution to launch multi-messenger astronomy at ultra-high-energies. A design has been proposed for the GRAND detector, and the instrumentation is being tested and optimized with 3 small-scale prototypes: GRAND@Nançay, GRAND@Auger, and GRANDProto300. Based on these pathfinders, the GRAND Collaboration is starting to explore improved GRAND technical designs for the next large-scale phase of the project. This will consist in two arrays of 10'000 km2 each, in the Northern and Southern hemispheres to be deployed from 2028. In this talk, we will present the status of the GRAND prototypes, the preliminary designs and simulation results for the next stages, and the rich research program that these will enable.