Physics at a High-Luminosity LHC with ATLAS

The physics accessible at the high-luminosity phase of the LHC extends well beyond that of the earlier LHC programme. Selected physics goals, spanning from Higgs boson physics to new particle searches and rare top decays, are presented in this document. They illustrate the substantially enhanced physics reach with an increased integrated luminosity of 3000/fb, and motivate the planned upgrades of the LHC machine and ATLAS detector. Disclaimer: This note has been updated in ATL-PHYS-PUB-2012-004. The update supersedes the Higgs section of this note and reports additional studies on vector-boson scattering.