Light Particles in the Lab and in the Sky

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

This award funds the research of Professor Julian Heeck at the University of Virginia. The search for --- and study of --- elementary particles has contributed greatly towards our understanding of nature for over a century. New particles, as motivated for example by the existence of dark matter or the phenomenon of neutrino oscillations under which the different neutrinos exchange their identities as they fly through space, could have escaped our detection not because they are extremely heavy, as often assumed, but rather because they have feeble interactions with the particles that we can more readily observe. Such light feebly-interacting particles are the focus of Professor Heeck's research. Axions and sterile neutrinos are prominent examples of such particles, but many other well-motivated models exist that will be systematically and thoroughly explored in this project, both from a theoretical perspective and in terms of their detectability in present and future experiments. Professor Heeck will focus on the exploration of novel search strategies that may unlock new research perspectives. The results of such studies could potentially broaden the physics motivations for many experiments and ultimately lead to the ground-breaking discovery of entirely new elementary particles, thereby advancing the national interest in fundamental science. This project also has significant broader impacts. By touching upon many different areas of particle physics, this project provides ample training ground for graduate and undergraduate students. Professor Heeck will also organize workshops that will connect particle physicists in the southeastern United States. More technically, Professor Heeck will construct a catalog of viable and testable extensions of the Standard Model involving light new particles, including many that have not been discussed in the literature before. These particles will be embedded in effective field theories as well as in realistic renormalizable models, with an emphasis on models that solve one or more of the outstanding problems of particle physics. The phenomenology of these particles will be studied exhaustively, most importantly at intensity-frontier experiments (e.g., Belle II, DUNE, and Mu2e) that have the precision and statistics to find feebly-coupled particles in rare decays and collisions. For each candidate, the optimal search signature that suppresses the Standard-Model background will be identified, ranging from missing-energy searches to displaced-vertex signatures. In addition to these direct searches in the laboratory, indirect signatures at the cosmic frontier --- most notably potential modifications of the cosmic microwave background --- will also be taken into account. Furthermore, their feeble couplings could render these particles natural dark-matter candidates or mediators to a larger dark sector --- an idea which will also be explored in this project. Viewed holistically, this project will thus promote light feebly-interacting particles as a complement to existing studies of heavy new particles, and will help to maximize our chances of finding new elementary particles and forces. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.