The Standard Model of particle physics, established over several decades, successfully describes the interactions of all known particles at energies accessible to today's experiments. However, there is definitive observational evidence that most of the matter content of the Universe is composed of an entity (given the name "dark matter") that cannot fit into the framework of the Standard Model. Understanding the identity and cosmological history of dark matter constitutes one of the most important problems in theoretical physics. Moreover, this quest is likely to unveil new physical laws or selection principles, shedding light on a host of associated fundamental questions in particle physics. As such, it is a matter of great national interest. In his research, Professor Sinha will explore the potential of future gravitational wave detectors and X-ray telescopes to probe dark matter physics, studying two leading candidates: the axion and primordial black holes. Through his work, Professor Sinha will thus be investigating ways to discover the most abundant particle in the Universe. This project will involve postdoctoral scholars as well as graduate and undergraduate students, providing critical training for the next generation of junior physicists. He will disseminate his work through public lectures and develop new courses based on his research findings, further enhancing the project's broader impacts. More technically, Professor Sinha will study axions from neutron star