Research in Particle Theory, Cosmology, and Quantum Gravity

This award funds the research activities of Professors Peter W. Graham and Ken Van Tilburg at Stanford University. One of the deepest puzzles in modern science is the nature of dark matter, an invisible substance that makes up most of the mass of the universe but has never been detected in a laboratory, together with the broader question of what physical laws operate beyond those already known. Answering these questions demands both imaginative new theoretical ideas and powerful new ways to measure the faintest signals in nature. Under this award, Professors Graham and Van Tilburg will develop novel experimental and observational strategies to search for dark matter and other new particles and forces, ranging from ultra-sensitive laboratory devices that exploit the quantum behavior of trapped particles and atoms, to new techniques for extracting information from the light of distant stars, supernovae, quasars, and galaxies. This research advances the national interest by promoting the progress of science in one of its most fundamental directions: the discovery and understanding of new physical laws. Because many of these techniques rest on the precise control and readout of quantum systems, the project also strengthens the nation's expertise in Quantum Information Science, with particular benefits for quantum sensing and measurement technologies more broadly. The project will also have significant broader impacts. Professors Graham and Van Tilburg will train graduate students and postdoctoral researchers, providing essential preparation for junior scientists entering the field, and will collaborate closely with experimental groups to turn theoretical ideas into working measurements. They will give public lectures, engage science journalists, and develop educational resources, including a comprehensive review article and an interdisciplinary workshop, that make these frontier topics accessible to students and the wider community, and Professor Graham will continue to strengthen undergraduate physics education at Stanford. Professor Graham will develop new laboratory methods to detect dark matter and other physics beyond the Standard Model. He will extend electron Penning-trap techniques, which use rapid measurement of an electron's quantum cyclotron state, to search for axion and dark-photon dark matter at lower masses through the trap's magnetron and axial modes. He will adapt electron and ion traps, and high-voltage charge accumulators to detect millicharged particles, which could make up (part of) the dark matter and are irreducibly produced by cosmic rays in the atmosphere. He will construct and test dark-sector models motivated by recent cosmological data and will design searches for inelastic and Higgsino dark matter through the "luminous" detection channel in large neutrino and dark-matter detectors. Building on the atom-interferometric MAGIS program, he will study the science reach of mid-band (0.01–10 Hz) gravitational-wave detectors, including improved source localization for "dark siren" measurements of the cosmic expansion history, and will advance a concept for microhertz gravitational-wave detection using atomic-clock comparisons with asteroid test masses. Professor Van Tilburg will develop intensity-interferometric techniques for particle astrophysics and cosmology, including scientific applications of Extended-Path Intensity Correlation (EPIC) for microarcsecond-level astrometry of compact sources. He will apply this to astrometric microlensing of multiply-imaged quasars to probe dark-matter substructure as small as an Earth mass, and will advance the Expanding Ejecta Method, which uses bright supernovae to obtain geometric distances and an independent calibration and measurement of the Hubble constant. On the theory side, he will study novel dark-sector dynamics, including bosonically enhanced self-interacting dark matter (together with Graham) and long-range scalar-mediated forces, and will refine three precision-frontier search strategies: the piezoaxionic effect, the spin-dependent ferroaxionic force, and scalar-mediated wake forces, carrying out the nuclear, atomic, and cosmological calculations needed to turn these ideas into concrete laboratory observables. 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.