Princeton University Gravity Group Lunch Seminar

Dark matter not only provides the invisible scaffolding from which the birth of galaxies takes place, but by studying its distribution in our universe we can infer a great deal of information regarding the growth of structure and cosmic expansion. Measuring the gravitational lensing of the CMB allows the mapping of all the matter distribution (for which the majority is dark matter) to very high redshifts. New observations with the Atacama Cosmology Telescope will allow CMB lensing to be determined at the ~2% level. This high signal-to-noise lensing spectrum will translate into a few percent determination of sigma_8, hence providing a robust test of low amplitudes reported by galaxy lensing surveys and one of the tightest constraints on the sum of neutrino masses. This measurement also sets the foundation for ground-based high-resolution lensing covering a large fraction of the sky.
In the first part of my talk, I will explore the implications of our measurement in the context of structure growth and discuss in detail the novel methods used to tackle key systematics affecting precision lensing related to atmospheric noise and extragalactic foregrounds. I will also highlight some of the main null tests from our comprehensive test suite used to deliver this robust state of the art lensing measurements. For the second part of my talk, I will discuss the prospects of using CMB lensing as a probe of the high-redshift structure only by 'delensing' the low redshift content of CMB lensing using correlated tracers like galaxy surveys, resulting in a map of high-redshift structure alone. This opens up a window to explore cosmological periods uncharted by other probes, enabling measurements of structure growth and providing rigorous confrontations between theory and observations within a redshift range where little information is otherwise available.