Six Things That Are Probably Not Dark Matter

by Ian Holst (U. Chicago)

Wednesday 5 Aug 2026, 12:30 → 14:30 America/Los_Angeles

48/2-224 - Madrone (SLAC)

The study of dark matter presents an opportunity to learn more about the fundamental particles that make up our universe and their impact on cosmological evolution and astrophysical phenomena. We focus on both particle dark matter and primordial black holes to explore their predictions and constraints in various scenarios, as well as their potential links to other mysteries in cosmology and astrophysics. In particular, we propose several particle models which not only generate the observed abundance of dark matter, but also have implications for the muon's magnetic moment, the electroweak hierarchy problem, and neutrino masses. We also show that dark matter production by both freeze-in and freeze-out mechanisms generates small isocurvature perturbations that are not constrained by observations of the cosmic microwave background. Using data from the Fermi Gamma-Ray Telescope, we constrain the properties of millisecond pulsars in our galaxy, with consequences for the Galactic Center GeV gamma-ray excess. We explore the rich phenomenology of a period of primordial black hole domination, which leads to enhanced black hole clustering and merging, leaving behind merged relics that live for long after the initial population has evaporated. If primordial black holes serve as dark matter, we find that when they encounter and are captured by neutron stars, their orbits can be vulnerable to tidal disruption by nearby bodies, limiting constraints on their abundance from that process.