Searches for vector-like quarks and ttbar resonances with the ATLAS detector

Various extensions of the Standard Model predict the existence of new types of quarks. We report on several search channels such as vector-like quarks decaying to a Higgs boson and a top quark or to a $W$ boson and a $b$ quark. The talk presents results from searches for new resonances decaying to a top-antitop pair, including the use of boosted top quark reconstruction techniques. These searches use the data sample recorded in 2012 at $\sqrt{s}=8$~TeV centre-of-mass energy by the ATLAS experiment at the LHC.