  The discovery of a Higgs-like boson with mass near 126 GeV, at the LHC, has
reignited interest in future energy frontier colliders. We propose here a
proton-proton (pp) collider in a 100 km ring, with center of mass (CM) energy
of ~100 TeV which would have substantial discovery potential for new heavy
particles and new physics beyond the Standard Model. In the case that LHC
experiments have already found exotic resonances or heavy "partner" particles,
this collider could fill out the "tower" of resonances (thus e.g. confirming an
extra dimension) or the full suite of partner particles (e.g. for
supersymmetry). The high luminosity of the new collider would enable unique
precision studies of the Higgs boson (including Higgs self coupling and rare
Higgs decays), and its higher energy would allow more complete measurements of
vector boson scattering to help elucidate electroweak symmetry breaking. We
also discuss an e+e- collider in the same 100 km ring with CM energies from 90
to 350 GeV. This collider would enable precision electroweak measurements up to
the ttbar threshold, and serve as a Higgs factory.
