Recent decades have seen an impressive improvement in our understanding of the content and history of the universe. Yet there are still some crucial pieces of cosmology which remain unknown. Dark matter (DM) is the majority of matter in our universe, but its nature is a mystery. Further, the initial conditions of our universe, which gave rise to all the structures we see today, are only partially understood. We propose a new technique for observing small-scale structure in dark matter which can teach us both about the beginning of the universe and the nature of dark matter itself.
Currently we can observe the largest structures in the universe, down to dark matter halos as small as 10^9 solar masses, also known as ultra-faint dwarf galaxies (UFDs). DM structures smaller than this are challenging to observe as they do not form stars. These structures, if found, will be a treasure-trove of information.
Our project proposes to study these small halos via their gravitational effects on the stars in UFDs. We will develop precise calculations for the effects of these halos in a UFD. Then we will study the implications for the nature of DM and the initial conditions of the universe. Our study will constrain variations in the universe's initial density at unprecedented length scales: much lower than methods like cosmic microwave background or Lyman alpha measurements. This will help test models for the birth of the universe in inflation, as well as theories of low-mass DM which leave imprints in these initial conditions. We will also explore implications for the nature of DM. For example, we can learn about self-interactions of DM through their effects on this small-scale structure. We also aim to test DM production mechanisms, DM dissipation, and potential new forces on DM via their impact on small-scale structure. This work is expected to inspire searches for fainter and more compact dwarf galaxies which could further improve sensitivity to these models of DM.
