Cosmology seminar: Searching for New Physics in the Universe's Oldest Light with the Atacama Cosmology Telescope

I will discuss recent and ongoing work focused on attempts to restore concordance amongst cosmological data sets, motivated by discrepancies amongst some measurements of the cosmic expansion rate (H_0) and the matter clustering amplitude (S_8). Particular attention will be paid to models invoking new physics at or prior to recombination, including quasi-accelerating early dark energy models and small-scale baryon-clumping scenarios (e.g., due to primordial magnetic fields). In particular, I will discuss constraints on these models derived using the latest data from the Atacama Cosmology Telescope (ACT). I will conclude with a look ahead to forthcoming CMB measurements from ACT, which will provide a powerful test of these models in the low-noise, high-resolution regime.