Extracting the universe’s expansion history from small-scale structure

          @misc{ scivideos_PIRSA:25080034,
            doi = {10.48660/25080034},
            url = {https://pirsa.org/25080034},
            author = {},
            keywords = {Cosmology, Particle Physics, Strong Gravity},
            language = {en},
            title = {Extracting the universe{\textquoteright}s expansion history from small-scale structure},
            publisher = {Perimeter Institute for Theoretical Physics},
            year = {2025},
            month = {aug},
            note = {PIRSA:25080034 see, \url{https://scivideos.org/index.php/pirsa/25080034}}
          }
          

Abstract

How did the universe evolve prior to the creation of the cosmic microwave background? There are no direct observational probes of the universe’s expansion history prior to the onset of Big Bang nucleosynthesis (BBN), and numerous theories predict deviations from radiation domination during the universe’s first second. Meanwhile, a persistent discrepancy between local and cosmological measurements of the Hubble constant has prompted us to reconsider the evolution of the universe between BBN and recombination. 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. Both cases illustrate how small-scale structure provides a powerful probe of the evolution of the universe prior to recombinatio