SUMMARY OF SNOWMASS ACCELERATOR GROUP M2 ON E+ E- CIRCULAR COLLIDERS

Perform a survey of the present status as well as the vision of the future promises of the various electron-positron circular colliders. The colliders to be covered include those currently in operation, currently under construction, or envisioned as a possibility of the future, and in the US and abroad. Special emphasis should be placed on the clear identification of the beam physics limits and technological limits, and an examination of the extent that they have been address by past research or need to be addressed by future research. Identify new and promising ideas even though they may need additional work. These issues should be addressed for all the leading technical realizations of the circular positron-electron colliders. Finally, the group should summarize in a brief report the highest priority research topics for different technological realizations of circular electron-positron systems and give an approximate timetable for key R and D development [1]. The group is also asked to provide a comprehensive presentation to high-energy and accelerator physicists in plenary sessions during the Snowmass workshop