Dark Sectors and New, Light, Weakly-Coupled Particles

The Standard Model (SM) of particle physics has achieved remarkable success as a result of several decades of exploration, of constantly pushing the boundaries of our knowledge of theory, experiment, and technology. However, while the SM provides a theoretically consistent description of all known particles and their interactions (ignoring gravity) up to the Planck scale, it is clearly incomplete as it does not address several pieces of evidence for new physics beyond the SM. One particularly powerful piece of evidence for new physics comes from the existence of dark matter (DM). DM dominates the matter density in our Universe, but very little is known about it. Its existence provides a strong hint that there may be a dark sector, consisting of particles that do not interact with the known strong, weak, or electromagnetic forces. Given the intricate structure of the SM, which describes only a subdominant component of the Universe, it would not be too surprising if the dark sector contains a rich structure itself, with DM making up only a part of it. Indeed, many dark sectors could exist, each with its own beautiful structure, distinct particles, and forces. These dark sectors (or “hidden sectors”) may contai