High Energy Physics

Gravitational waves (GW) offer a unique window into primordial density perturbations that may differ significantly from the adiabatic fluctuations observed in the CMB and large-scale structure. This raises an exciting prospect of seeing fluctuations of a completely new field from inflation in the anisotropy patterns of GW maps. However, CMB constraints impose an apparent tradeoff between distinctive anisotropy and sizable isotropic signal of such a GW background. I will show that rotating axion-like fields can naturally circumvent this limitation, producing both a strong GW background and large anisotropies within it. I will present the key characteristics of this signal and explore its detection prospects with future GW experiments.

The past decade has seen rapid advancement in electron excitation-based direct detection experiments, which target light, MeV-GeV mass dark matter. Recently, the DAMIC-M collaboration began to probe the benchmark light dark matter models, renewing questions about the broader range of dark matter models these experiments can detect, and the necessity of new experiments to search beyond. In this talk we'll discuss a novel mechanism to cosmologically produce light, keV-GeV mass, dark matter coupled to electrons via a magnetic dipole moment. We consider a minimally extended dark sector in which only heavier states are charged under the kinetically mixed dark photon. These states are produced via freeze-in and subsequently thermalize the rest of the dark sector, efficiently populating the lighter, neutral, magnetic dipole-coupled dark matter. Finally, we'll discuss how magnons, collective excitations of spin waves, can be used to search for keV-MeV mass magnetic dipole-coupled dark matter, outside the reach of any semiconductor based direct detection technology.