  We introduce a new way of modelling the physics beyond the Standard Model by
considering fake, strictly off-shell degrees of freedom: the fakeons. To
demonstrate the approach and exemplify its reach, we re-analyse the
phenomenology of the Inert Doublet Model under the assumption that the second
doublet is a fakeon. Remarkably, the fake doublet avoids the most stringent
$Z$-pole constraints regardless of the chosen mass scale, thereby allowing for
the presence of new effects well below the electroweak scale. Furthermore, the
absence of on-shell propagation prevents fakeons from inducing missing energy
signatures in collider experiments. The distinguishing features of the model
appear at the loop level, where fakeons modify the Higgs boson
$h\to\gamma\gamma$ decay width and the Higgs trilinear coupling. The running of
Standard Model parameters proceeds as in the usual Inert Doublet Model case.
Therefore, the fake doublet can also ensure the stability of the Standard Model
vacuum. Our work shows that fakeons are a valid alternative to the usual tools
of particle physics model building, with the potential to shape a new paradigm,
where the significance of the existing experimental constraints towards new
physics must necessarily be reconsidered.
