Searches for vector-like quarks and $t\bar{t}$ resonances with the ATLAS detector

Searches for vector-like quarks and $t\bar{t}$ resonances are performed with the ATLAS experiment at the Large Hadron Collider using an integrated luminosity of 14.3~fb${}^{-1}$ of proton-proton collisions recorded in 2012 at a center-of-mass energy of $\sqrt{s}=$ 8~TeV. Several final states have been exploited to carry out these searches such as lepton plus jets and opposite and same-sign dilepton final states. No significant excess of events above the Standard Model expectation is observed, and upper limits at 95$\mathrm{\%}$ CL are derived for vector-like quarks of various masses in a two-dimensional plane of branching ratios, and for $t\bar{t}$ resonances in two benchmark models, a topcolor leptophobic $Z^{\mathrm{\prime }}$ and a Kaluza-Klein gluon.