Prompt cusps
[More detail] [Outreach article]
When gravitational collapse breaks the smooth mass distribution of the early universe, the process immediately produces a compact structure in which density scales with radius as ρ ~ r^-1.5 (see this video). I find no evidence that these prompt density cusps are destroyed as the halos around them grow. Since every halo and subhalo in the universe formed from an initial gravitational collapse event, this result suggests that a prompt cusp should reside inside every one of them. This outcome has significant observational consequences for cold and warm dark matter models.
Gravitational detection of dark systems
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Dark matter halos are known to surround galaxies, but the vast majority of halos are expected to be devoid of stars and gas, so they are difficult to detect. However, they can perturb the motions of stars, dynamically heating stellar systems and producing characteristic patterns in stellar positions and motions. I am using analytic methods to connect the statistical properties of a gravitationally perturbed stellar system to those of its dark perturbers.
Formation of halos prior to the matter epoch
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If initial variations in the density of the universe are sufficiently extreme at small scales, dark matter halos can form prior to the matter-dominated epoch, which began at a time of about 52000 years. I found that while gravitationally bound structures cannot form where radiation dominates, convergent particle drift can cause localized regions to become matter dominated and form bound halos long before radiation globally gives way to matter. These haloes would be around a trillion times more internally dense than the halos that surround galaxies.
Probing the early universe using dark matter minihalos
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The first gravitationally bound objects in the Universe were small, potentially Solar System–scale dark matter minihalos. These objects are broadly expected to survive today, and their potentially observable characteristics represent a probe of the primordial mass distribution at otherwise inaccessibly small scales. Consequently, they represent a unique probe of the late stages of inflation and the early postinflationary period. I use N-body simulations and mathematical modeling to decipher the connection between minihalos today and primordial cosmology.
Predicting populations of dark matter halos
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All cosmic structure grew out of initially minor variations in the density of the Universe. This structure manifests visibly as galaxies, but it is dominated by invisible dark matter. Dark matter clusters into gravitationally bound halos that represent the building blocks of structure. The problem of predicting a halo population from the precursor mass distribution is a longstanding one, but I am developing new ways to approach this problem. My approach begins with the first halos, following their evolution as they cluster to produce later generations of halos.