Limits on Four-Top Production from the ATLAS Same-sign Top-quark Search
  We repurpose the recent ATLAS search for same-sign top quarks in data with 1.0 fb$^{-1}$ in the context of a search for production of four top quarks. Using the null results of that search, we place limits on the four-top-quark production cross section of about 1 pb. These limits are larger than the expected Standard Model rate for four-top-quark production, but are already strong enough to place interesting constraints on models which enhance that rate. We interpret these results in the context of models in which the right-handed top quark is composite and find limits on the compositeness scale of about 700 GeV. 
Ning Zhou, Daniel Whiteson, Tim M.P. Tait
hep-ph hep-ex