Description
The advent of Stage-IV spectroscopic surveys such as DESI and photometric surveys such as LSST has provided a unique opportunity to study the temporal evolution of cosmological parameters using tomographic binning via cross-correlation. Cross-correlation, especially when considering two particularly dissimilar tracers such as galaxy surveys and CMB lensing, have been largely considered to be systematics free. However, the demands of ultra-precise measurements imply that we have to consider systematics that were previously hidden under statistical uncertainties or assumptions of independence. In this talk, I will use DESI Emission-Line Galaxies and LSST Lyman-Break Galaxies as case studies to underpin new sources of foreground systematics. I will also discuss possible new simulation requirements necessary to report unbiased and precise cosmological parameter measurements.
