Probing Dark Sector Physics in Collider and Cosmology

University Of Notre Dame, Notre Dame IN

Investigators

Abstract

This award funds the research activities of Professor Yuhsin Tsai at the University of Notre Dame. Imagine the possibility that there is another "hidden" world that coexists with ours in the same space and time, but which is practically invisible to us because the interactions between the hidden world and ours are very weak. While this may sound like science fiction, recent developments in particle physics and cosmology have shown that an invisible sector of the universe might actually exist. Indeed, the existence of such a hidden sector would help explain several long-standing theoretical and observational puzzles. Professor Tsai’s research is aimed at using gravitational waves, early-time cosmology, and high-energy particle colliders (such as the Large Hadron Collider) to uncover such hidden worlds. As such, this research advances the national interest by promoting the progress of science in the discovery of new physical laws and new components of the natural world. This work will also have several broader impacts. The results of this work will not only guide future experiments and technology development, but also involve graduate students and postdocs, thereby providing critical training for junior physicists beginning research in this field. Professor Tsai also intends to give public lectures on his research results and help to develop outreach programs for high-school students. More technically, Professor Tsai will study energy perturbations in the stochastic gravitational-wave background. He will also study the size of non-Gaussian signatures of the gravitational-wave signal produced by the hidden particles in the early universe. The result of this analysis will help in the identification of the gravitational-wave detectors that can observe the energy fluctuations from the hidden world that interacts with us solely through gravity. Professor Tsai will also study the cosmological signatures of models that address the Higgs hierarchy problem, such as the Mirror Twin Higgs model and the N-Naturalness model. Based on the idea that these scenarios can produce acoustic oscillations between hidden particles, we can study these model through the changes they induce for gravity perturbations in the early universe. Exploiting the current and the expected future sensitivity of the LHCb experiment, Prof. Tsai will also develop new ways to study the signature of long-lived particles that couple not only to regular matter but also to particles in the hidden world. 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.