The Giant Radio Array for Neutrino Detection (GRAND) and its prototype phases

Abstract: Multi-messenger astronomy is key today to broaden our understanding of the high energy Universe. When an ultra-high energy (UHE) particle interacts in the atmosphere or underground, it initiates an extensive air shower that produces a coherent radio emission in the 50-200 MHz range. The GRAND project is an envisioned observatory of UHE particles (cosmic rays, gamma rays and especially neutrinos) that will consist of 200,000 radio antennas deployed over 20 different locations each of $\sim$ 10,000 $\rm km^2$. In its current phase, it consists of 3 prototypes running autonomously in 3 different locations: GRAND@Auger in Argentina, GRAND@Nan\c{c}ay in France and GRANDProto300 in China, all at commissioning stage. The first goal of these pathfinders is to demonstrate the viability of the GRAND detection concept. GRANDProto300 will also propose a rich science case, by allowing the study of the transition between galactic and extra-galactic cosmic ray sources. In the following, we present the detection concept, the preliminary designs and layout and the ongoing developments of the experiment.