A clean signal for a top-like isosinglet fermion at the Large Hadron Collider

We predict a clean signal at the Large Hadron Collider ( $sqrt{s}=$ 14 TeV) for a scenario where there is a top-like, charge +?2/3 vector-like isosinglet fermion. Such a quark, via mixing with the standard model top, can undergo decays via both flavour-changing Z-boson coupling and flavour-changing Yukawa interactions. We concentrate on the latter channel, and study the situation where, following its pair production, the heavy quark pair gives rise to two tops and two Higgs bosons. We show that when each Higgs decays in the $bbar{b}$ channel, there can be a rather distinct and background-free signal that can unveil the existence of the vector-like isosinglet quark of this kind.