Grant: Subatomic Physics Envelope - Individual

Dark matter is an important ingredient of our universe. It comprises more than 80% the matter energy density today and its gravitational effect drives structure formation from galactic to cosmological length scales. However, after decades of search, the fundamental nature of dark matter remains undetermined. This strongly calls for new ideas and proposals that broaden the theoretical and experimental perceptions of dark matter. An exciting direction I will pursue is novel theoretical connections between dark matter and neutrino, in the context of sterile neutrino dark matter and neutrino portal dark sector theories. My recent works pointed out a new connection between sterile neutrino dark matter and self-interaction among active neutrinos. The self-interaction mediated by a light scalar or vector boson can address the observed relic abundance and lift the strong indirect detection limits. I will continue my effort in exploring the predictions from such a theoretical framework, with the goal of fully testing the relic target through a series of particle, astrophysical and cosmological measurements. Other than relic abundance, there exists further information on the nature of dark matter in cosmological data. For example, the above sterile neutrino dark matter production mechanism features a novel primordial phase space distribution and can be constrained via small-scale structure observations. Another attractive class of dark matter candidates is the self-interacting one which can solve the mass profile problem of dwarf galaxies. I will explore the possibility of neutrino playing the role of dark force carrier. Such theories require a tight coupling of dark matter with neutrinos and have rich interplay with particle physics probes. With the diverse ongoing particle physics experimental program in search of new physics, it is important to broaden the spectrum of dark matter theories and forms and the corresponding new search strategies. Inspired by the rich theory structure that describes luminous matter, I will explore the impact of bound state physics on dark matter properties, from simple two-body states to ''dark matter nuggets'' with a large number of particles clumping together by an attractive dark force. The presence of bound states can strongly affect the interpretation of dark matter search results and predict novel, spectacular signals for unveiling the nature of dark matter. Moreover, I will explore connections of dark matter with other open questions in fundamental physics, including the origin of cosmic baryon asymmetry, neutrino masses, and the strong CP problem of the Standard Model. My research program will contribute new theoretical tools for understanding these puzzles and our universe, present novel guidance for experimental efforts in Canada and around the world, and offer ample opportunities in the training of HQP.