Four-top production and t t + missing energy events and multi TeV e+e- colliders

Four-top production and top pair production in association with missing energy e+ e- colliders are sensitive probes of beyond-the-Standard-Model physics. We consider Standard Model extensions containing a new U(1)' which couples preferably to the most massive states of the S M such as the top quark or Dark Matter but has suppressed couplings to all the light states of the S M, as inspired by Randall-Sundrum-like setups or theories of partial fermion compositeness. These simple models are poorly constrained by experimental data but lead to striking new signatures at colliders. In this paper we consider Z' production in association with a top quark pair in 3 TeV e+ e- collisions at CLIC, leading to interesting four-top final states and t t + Emiss events.