Institute for Advanced Study/Princeton University Early Universe/Cosmology Lunch Discussion

Abstract 1: The CDM scenario predicts an entire hierarchy of dark substructure within the Milky Way halo that is, barring any annihilation signal, only detectable gravitationally. Cold tidal streams from disrupting globular clusters have been proposed as promising objects to search for these gravitational signatures, in particular by searching for gaps along streams. I will present a new approach to describing the stream-substructure interaction, which focuses on the much more prevalent weak stream perturbations. This approach allows us to directly and semi-analytically predict statistics such as the one-dimensional power spectrum of stellar density and velocity along the stream (based on https://arxiv.org/abs/2108.13420).

Abstract 2: The epochs of cosmic dawn and reionisation present promising avenues for understanding the role of dark matter (DM) in our cosmos. The first galaxies that populated our Universe during these eras resided in DM halos that were much less massive than their counterparts today. Consequently, observations of such galaxies can provide us with a handle on the clustering properties of DM in an otherwise inaccessible regime. In this talk, I will show how high-redshift UV galaxy luminosity-function (UV LF) data from the Hubble Space Telescope can be used to study the clustering of DM at small scales. In particular, I will show how it provides a measurement of the matter power spectrum at wavenumbers 0.5 Mpc^-1 < k < 10 Mpc^-1, after marginalising over astrophysical parameters. This measurement covers the uncharted redshift range 4 <= z <= 10 and reaches scales beyond those covered by Cosmic Microwave Background and Large-Scale Structure observations.