Constraining cosmology with CMB lensing from ACT DR6+

The weak gravitational lensing of the cosmic microwave background photons due to the line-of-sight matter distributions from large-scale structure is a powerfully precise probe of cosmology, allowing us to map out our post-recombination cosmic history and rigorously assess the validity of our fiducial cosmological model, Lambda-CDM. In this talk, I will demonstrate how we've measured the CMB lensing power spectrum from the final data release from the Atacama Cosmology Telescope (ACT). I will be highlighting various improvements in our analysis from ACT Data Release 6 (DR6), such as the novel usage of daytime observations as well as improved techniques to process CMB data jointly with Planck. Demonstrating robustness by briefly showcasing our comprehensive suite of null tests and foreground assessments, I will then finally showcase state-of-the-art constraints on structure growth in the form of S_8^{lens} as well as the sum of neutrino masses, the Hubble constant, and more, interpreting these in the context of today's cosmic tensions while glimpsing at the prospects of sub-percent precision measurements of cosmology with the Simons Observatory.