• Physics and Astronomy Colloquium

October 30, 2026 3:30 PM - October 30, 2026 4:30 PM
PAIS 1100

Host:

Francis-Yan Cyr-Racine

Presenter:

Dr. Ken van Tilberg (Stanford)

The ΛCDM paradigm robustly predicts dark matter halos with a roughly scale-invariant spectrum over an enormous range of mass scales, potentially below stellar or even planetary mass. Yet, no observation has ever probed this substellar regime, even though it is one of the sharpest available tests of DM microphysics. I will describe a technique that will make this possible: high-precision differential astrometry of multiply imaged quasars over a decade-long survey. Each quasar image's light threads through substructure of a lens galaxy/cluster, picking up a stochastic sequence of gravitational deflections. This produces a random walk (in the apparent celestial position) with a calculable, red-tilted power spectrum that appears as excess astrometric noise between image pairs, or, for larger halos, as an anomalous angular acceleration. With sub-microarcsecond differential precision, within reach of proposed interferometers, this could reach the standard CDM halo population down to an Earth mass, twelve orders of magnitude below the smallest DM structures detected to date. A positive detection would drastically improve universal lower bounds on the mass of the DM particle, constrain its kinetic decoupling from the Standard Model, and probe the primordial power spectrum far beyond scales probed by CMB+LSS; a null result would be equally informative. I will present sensitivity forecasts for two benchmark lens systems and the observational path to get there.

Biography

My research explores new ways to probe physics beyond the Standard Model, with a focus on dark matter and hidden sectors of the universe. My work spans particle physics, astrophysics, and cosmology, using precise instruments and cosmic phenomena to search for new physics. My group investigates topics like stellar basins, dark matter lensing through stellar motions, exotic axion-mediated forces, and ultra-high-resolution interferometry. A common thread is using subtle signals—from atomic clocks to quasars—to uncover deep physical laws.