Roman will be one of the most powerful facilities for weak lensing cosmology ever built, with the angular resolution, stability, and infrared sensitivity afforded by space-based observations. Forecasts imply that the weak gravitational lensing (WL) in a ∼2000 sqdeg HLIS with Roman can measure the amplitude of matter fluctuations with an order of magnitude improvement in precision over current measurements. At least as critical is the improved control of systematics and the new avenues for extracting cosmological information from small scales and non-Gaussian statistics that are enabled by the gains in redshift coverage, galaxy number density and image quality with Roman. These measurements have the potential to revolutionize our understanding of cosmology, gravity, and fundamental physics.

Delivering on this promise is an enormous challenge. Exploiting such an increase in statistical precision requires comparable improvements in both the control of instrumental and astrophysical systematics, and the accuracy of model predictions. We are tasked with a program of infrastructure development that will enable the Roman HLIS to achieve its extraordinary cosmological potential, while simultaneously providing exquisite data for an extensive range of astrophysical investigations. We have planned our work tightly around a list of deliverables, grouped under the broad categories of: survey strategy, weak lensing measurements, cosmological inference, and community engagement.

Our team comprises leading experts on these topics, many of whom have been deeply involved with Roman for a decade or more. The infrastructure proposed here will build heavily on the work that we have done as members of the Science Investigation Teams (SITs). It also builds on our team’s experience with previous surveys such as the Sloan Digital Sky Survey (SDSS), the Dark Energy Survey (DES), and the Hyper-Suprime Cam (HSC), as well as work ranging from early formulation to implementation of the Euclid Space Telescope (Euclid), the Vera Rubin Observatory’s Legacy Survey of Space and Time (Rubin), and the Spectro-Photometer for the History of the Universe and Ices Explorer (SPHEREx). Roman’s depth, angular resolution, and infrared coverage distinguish it from other large surveys: while we leverage synergies with other projects whenever possible, we will develop Roman-specific methods and pipelines to realize its full potential. We look forward to working with the Roman Project, the Science Operations Center (SOC), and the astronomy community.

Recent weak lensing measurements provide suggestive but not yet compelling evidence for a ∼5% discrepancy between matter clustering in the low-z universe and the predictions of cosmic microwave background (CMB)-normalized cosmological models that assume general relativity (GR): the “S8 tension”. If this tension continues to hold, then Roman (also Rubin, and Euclid) will confirm it and map out its scale, environment, and redshift dependence. Our plan is designed around the more conservative scenario in which any such conflict is at the ≲ 1% level, and requires the full power of next-generation facilities to detect, or rule out. However, the required analysis tools are similar under these two scenarios, and we have the flexibility to adjust if the conflict between predicted and observed matter clustering becomes more compelling.