Particle Physics

It has been recently pointed out that variable weak gravitational lensing effects on the motion of background stars can be used to probe nonluminous structures inside the Milky Way halo. I will describe one possible detection strategy targeting collapsed dark matter structures in the mass range from million to billion solar masses. The data analysis technique will be discussed in detail with an application to the second data release of Gaia.

We propose a novel design of a laboratory search for axions based on photon regeneration with superconducting RF cavities. Our particular setup uses a toroid as a region of confined static magnetic field, while production and detection cavities are positioned in regions of vanishing external field. This permits cavity operation at quality factors of Q ~ 10¹⁰ - 10¹². The limitations due to fundamental issues such as signal screening and back-reaction are discussed, and the optimal sensitivity is calculated. This experimental design can potentially probe axion-photon couplings beyond astrophysical limits, comparable and complementary to next generation optical experiments.

The stability of dark matter and its interactions with the Standard Model remain some of the biggest mysteries of our time. Instead of inventing ad hoc stabilization symmetries I propose to economically use the existing baryon and lepton number symmetries of the SM. This can lead to interesting signatures in terrestrial experiments, shower us in anti-helium, and keep neutron stars warm.

One of the leading hypotheses for dark matter is that it consists of bosonic particles with masses below the eV scale, such as axions, moduli and dark photons. Unlike spin-0 particles, spin-1 particles do not have a misalignment mechanism to produce the desired abundance of dark matter, and population of light dark photon dark matter has been an open question in cosmology. I will present a novel mechanism to produce light spin-1 dark matter in cosmology. The dark matter energy density is initially stored in an axion-like field which is misaligned from its minimum during inflation. This energy density is efficiently transferred to dark photons using tachyonic particle production. This mechanism opens up extensive parameter space for dark photon dark matter.

Statistical evidence has previously suggested that the Galactic Center GeV Excess (GCE) originates largely from point sources, and not from annihilating dark matter. In this talk, I will discuss the impact of unmodeled source populations on identifying the true origin of the GCE. In a proof-of-principle example with simulated data, I will demonstrate that unmodeled sources in the Fermi Bubbles can lead to a dark matter signal being misattributed to point sources. Furthermore, I will show there is striking behavior consistent with a mismodeling effect in the real Fermi data, finding that large artificial injected dark matter signals are completely misattributed to point sources. Consequently, I will conclude that dark matter may provide a dominant contribution to the GCE after all, and discuss future directions.

Atomic hydrogen gas clouds originating from the Galactic Center offer a novel way to test dark matter phenomenology. By exploiting the inefficient gas cooling rates at low temperatures, bounds for various interactions between dark and baryonic matter can be set. We demonstrate this new method and present limits for a number of dark matter models including ultra-light dark photons and super-heavy candidates.

New physics in the neutrino sector might be necessary to address anomalies between different neutrino oscillation experiments. Intriguingly, it also offers a possible solution to the discrepant cosmological measurements of H_0. 
We show here that delaying the onset of neutrino free-streaming until close to the epoch of matter-radiation equality can naturally accommodate a larger value for the Hubble constant, while not degrading the fit to the cosmic microwave background (CMB) damping tail. We achieve this by introducing neutrino self-interactions in the presence of a non-vanishing sum of neutrino masses. This "strongly interacting" neutrino cosmology prefers a 3+1 neutrino scenario, which has interesting implications for particle model-building and neutrino oscillation anomalies. Due to their impact on the evolution of the gravitational potential at early times, self-interacting neutrinos and their subsequent decoupling leave a tell-tale structure on the matter power spectrum. 
Our analysis shows that it is possible to find radically different cosmological models that nonetheless provide excellent fits to the data, hence providing an impetus to thoroughly explore alternate cosmological scenarios.