1-2pm: Extracting the Expansion History from Small-scale Structure

Since the growth of dark matter density perturbations depends on the expansion rate, deviations from the standard expansion history leave imprints on the matter power spectrum.  I will discuss how adding decaying massive particles or fast-rolling scalar fields to the standard cosmological model impacts the abundance and structure of dark matter halos. Introducing these components prior to the onset of Big Bang nucleosynthesis (BBN) can enhance structure growth on very small scales, leading to new constraints on annihilating dark matter. Meanwhile, scalar fields that dominate the universe after BBN can enhance the population of dwarf galaxies while suppressing power on intermediate scales. Both cases illustrate how small-scale structure provides a powerful probe of the evolution of the universe prior to recombination.