Abstract
Ultralight scalar fields coupled to photons or neutrinos can leave distinctive imprints on astrophysical observables, particularly through measurements of pulsar spin-down luminosities and black hole superradiance. If such scalars are sourced by the electromagnetic fields of neutron stars, they can develop extended long-range profiles, unlike axions, leading to observable effects on the redshift and pulsar spin-down rates. In this talk, I will discuss the interaction between scalar fields and the electromagnetic environment of highly magnetised stars and explore the resulting phenomenological consequences. I will also examine how scalar fields participating in black hole superradiance can be constrained when their interaction with the cosmic neutrino background suppresses the instability. By comparing theoretical predictions with observed black hole spin distributions, we can place strong bounds on the scalar-neutrino coupling, independent of whether these scalars constitute dark matter.
 

Link to Zoom registration:
https://zoom.us/meeting/register/fRu0KGneR7yR1ykQVPYu5w