Elusive dark matter and other exotic phenomena: A number of astrophysical measurements point to the existence of a new form of matter. For instance, the rotational speed of stars and observation of gravitational lensing effects strongly indicate the presence of so-called dark matter, in addition to our ordinary matter, that would compose a large fraction of our universe. Dark matter particles can be directly produced at the Large Hadron Collider, and one striking event signature would be the presence of an energetic jet of ordinary particles (called a monojet) and large missing energy due to dark matter particles escaping the ATLAS detector. As reported in the Journal of High Energy Physics (2018), a monojet final state constitutes a distinctive signature of beyond-Standard Model physics, and is also used to search for extra spatial dimensions and supersymmetry. Constraints have been set on various models.