Publications

Dark Matter Constraints from S-Stars Near Sgr A*

Observations have revealed a cluster (known as the S-Cluster) of star which travel extremely close to Sgr A* during their highly eccentric orbits. In models where dark matter accumulates in stellar interiors and then annihilates, dark matter annihilation could significantly affect the energetics of these stars. We find three observable phenomena: (1) dark matter annihilation can prevent stars from initially forming near Sgr A*, they must instead migrate from large distances, (2) dark matter annihilation can partially replace nuclear fusion, slowing down stellar evolution, (3) large dark matter annihilation rates can potentially disrupt the star, causing it to expand and cool off of the main sequence.

IGRB Limits on Dark Matter Cusps

Recent work has indicated that prompt ``cusps" containing highly compact dark matter structures can be produced in the early universe and survive until the present day throughout most of the galactic and extragalactic volume. In such scenarios, these cusps can dominate the total dark mattter annihilation rate of the universe due to their compact nature. This changes the morphology of the expected dark matter signal, making it more isotropic. We produce a new model for the isotropic gamma-ray background flux using 14 years of Fermi-LAT observations, and set strong constraints on dark matter annihilation in these scenarios, ruling out standard thermal models annihilation to bb up to masses of 120 GeV.

Dark Matter signals become brighter righter when inverse-Compton is modeled more accurately

Searches for cosmic-ray positrons are one of the most sensitive probes of dark matter annihilation. This is particularly true for leptophilic dark matter models that can be difficult to detect via other channels. The principle impediment to detecting the sharply peaked positron spectrum from leptophilic dark matter is the cooling of the positrons via synchrotron and inverse-Compton scattering, which has normally been treated via a simplified model that assumes these losses are continuous. We show that when the stochasticity of inverse-Compton losses is taken into account, the expected signal becomes twice as bright, making it easier to detect heavy dark matter.

Strongly Coupled Dark Matter Models Can Produce Antihelium 4

AMS-02 has tentatively detected a flux of antihelium nuclei (around 10 events in total). This observation, if confirmed, would be very exciting because antihelium is not supposed to be produced by standard astrophysics -- and would point towards new physics. More confusingly, a handful of these events may be consistent with antihelium 4 -- which is difficult to produce even in dark matter models. We propose the first realistic dark matter model capable of producing an observable antihelium 4 flux. If the WIMP is very heavy (near unitarity scale), and annihilates through a strongly coupled dark sector, then each annihilation will produce a shower of dark pions with very high multiplicity. If these particles quickly decay to standard model quarks through a portal interaction -- the result is a high multiplicity of baryons produced promptly at the same vertex. This significantly enhances the formation of heavy antinuclei, and makes observations of antihelium-4 possible.

Using Unusual Supernovae to Probe Dark Matter Interactions

Observations have uncovered a strange sub-category of supernovae, Ca-Rich Gap Transients, which are dim Type Ia supernovae that have spectral lines indicating an unusual abundence of Ca (indicative of an origin as low-mass white dwarfs), and a morphological distribution that makes them overabundent in the outskirts of galaxies. The fact that these systems are consistent with the explosion of low-mass (~0.5 solar mass) white dwarfs makes it difficult to utilize standard stellar or binary synthesis models to explain their evolution. The fact that they are found primarily in the outskirts of galaxies also suggests physics that does not correlate with the total star-formation rate. We propose a model where asteroid-mass primordial black holes collide with, and precipitate the explosions of these white dwarfs. We show that the morphology of these events is dominated by dwarf spheroidal galaxies orbiting around a host galaxy, and naturally explains the morphology of these systems.

Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination

The impressive regularity of pulsating neutron stars allow them to be used as extremely acurate "clocks" that operate on Myr or even Gyr timescales. Pulsar timing arrays have taken repeated observations of nearby MSPs over 20 Myr, looking for small deviations which may be due to local gravitational effects affecting either the neutron star environment or local solar neighborhood. We note that these arrays are quickly becoming sensitive to the enhanced dark matter substructure that is expected when the universe goes through a period of Early Matter Domination before the onset of radiation domination during big-bang nucleosynthesis. Current, or near-future, observations (20 years with approximately 70 pulsars), could begin to constrain novel EMDE parameter space -- while future studies including 200 pulsars over 40 years could raise the minimum energy floor for early matter domination as high as 150 MeV.

Celestial-Body Focused Dark Matter Annihilation

Dark Matter searches traditionally proceed through either direct methods (searching for dark matter scattering with standard model particles), or through indirect methods (through dark matter annihilation into standard model particles). We propose a new search that proceeds through a combination of scattering and annihilation. Dark Matter particles in the galaxy scatter with celestial bodies (most importantly brown dwarfs and neutron stars). They become trapped inside and their density increases until they annihilate. If this annihilation proceeds through a light-mediator capable of escaping the compact object, its subsequent decay into standard model particles can produce a detectable signature similar to standard annihilation. However, the morphology and amplitude of the signal have detectable differences because the annihilation rate depends on the rate of dark matter capture. We show that current gamma-ray constraints can place strong limits on the dark matter scattering cross-section in these models, outperforming both standard direct detection experiments and previous Solar gamma-ray searches.

Dark Matter Model Building