[Cosmology seminar] Gravitational-Wave Probes of Dark Matter

Virtually all the evidence we have for dark matter arises from its gravitational influence on baryons, radiation, and the large-scale structure of the Universe. Yet, the majority of experimental searches target non-gravitational couplings to the Standard Model, which remain elusive. Gravitational waves provide a complementary and model-independent way to search for dark matter, by probing the strongest gravitational fields in the Universe—those surrounding black holes and neutron stars—where dense dark matter configurations can form dynamically through gravity alone.

In this talk, I will discuss theoretical mechanisms through which different dark matter structures can develop in strong-field regimes, and how current and upcoming gravitational-wave observations can be used to probe them. I will also present the results of the first dedicated search for the imprints of light scalar fields on LIGO–Virgo–KAGRA black hole binaries. For the events GW190728 and GW190814, vacuum lies outside the 95% credible region. Interestingly, GW190728 shows tentative evidence for a scalar environment with a Bayes factor of lnB ~ 3.5 and is consistent with a light scalar of mass ~ 10^{-12} eV. While this constitutes only a tentative hint rather than conclusive evidence, it illustrates the growing power of gravitational-wave observations to test fundamental physics.