New Challenges and Big Questions for Accelerator Physics*

Studies of the fundamental properties of nature – quantum laws governing the subatomic world of nuclei, protons and neutrons, and tiny elementary particles – require advanced scientific tools with ever increasing reach and precision. Particle accelerators and colliders are instruments that enabled many fundamental discoveries in the past. The recent long-range planning reports produced in 2023 by the nuclear physics community, and by the particle physics community, outlined ambitious plans for accelerator-based exploration programs involving the Electron-Ion Collider and LBNF/PIP-II projects; a possible Higgs factory such as a linear collider ILC or circular collider FCC-ee, eventually leading to an energy frontier collider FCC-hh; or an advanced concept presently undergoing R&D – a muon collider or plasma wakefield acceleration collider. In this presentation, we will review the main questions that need to be answered on the path to the realization of these discovery machines, highlighting the unique challenges of each concept as well as discussing the themes that are common to any such collider.