Cosmology with Shadows in the Microwave Sky

Our current 6-parameter LambdaCDM cosmological model is well constrained by observations in the linear regime, such as measurements of the cosmic microwave background (CMB) radiation. A new frontier for cosmology is to search for departures from this model, which pushes future measurements into the non-linear regime (e.g., late-time growth of structure). The thermal Sunyaev Zel'dovich (tSZ) effect offers a unique way to probe the growth of structure using high-resolution CMB experiments, such as the Atacama Cosmology Telescope. I will review the recent tSZ cosmological constraints and discuss the astrophysical uncertainties that currently limit them. I will discuss current efforts to mitigate these astrophysical uncertainties highlighting the role that optical surveys like the Large Synoptic Survey Telescope will play. I will describe the prospects for future CMB experiments like the Simons Observatory and CMB-S4 to constrain departure from our standard cosmological model with tSZ observations.