  We investigate mono-top signatures arising from phenomenological models of
fermionic top-partners, which are degenerate in mass and decay into a bosonic
dark matter candidate, either spin-0 or spin-1. Such a model provides a
mono-top signature as a smoking-gun, while conventional searches with $t\bar t$
+ missing transverse momentum are limited. Two such scenarios: i) a
phenomenological 3rd generation extra dimensional model with excited top and
electroweak sectors, and ii) a model where only a top-partner and a dark matter
particle are added to the SM, are studied in the degenerate mass regime. We
find that in the case of extra dimension a number of different processes give
rise to effectively the same mono-top final state, and a great gain can be
obtained in the sensitivity for this channel. We show that the mono-top search
can explore top-partner masses up to 630 GeV and 300 GeV for the 3rd generation
extra dimensional model and the minimal fermionic top-partner model,
respectively, at the high luminosity LHC.
