Exotic decays of top partners with charge 5/3: bounds and opportunities

Abstract: Exotic decays of top partners in new bosons are the norm in realistic models of a composite Higgs. We focus on the custodial charge-$5/3$ partner, which normally decays exclusively into $tW^+$. The new channels include a colour-sextet, $X_{5/3} \to \bar{b} \pi_6$, as well as singly and doubly charged scalars, $X_{5/3} \to t \phi^+$, $b \phi^{++}$. We use existing same-sign lepton searches to show that the new final states are constrained at the same level as the standard one. At the same time, exotic final states also offer opportunities for improvement: examples include a hard photon in $X_{5/3}\rightarrow t\phi^+\rightarrow tW^+\gamma$ decays, and top-rich channels which arise in several exotic $X_{5/3}$ decays.