  The recently proposed Multi-coupled Dark Energy (McDE) scenario -
characterised by two distinct Cold Dark Matter (CDM) particle species with
opposite couplings to a Dark Energy scalar field - introduces a number of novel
features in the small-scale dynamics of cosmic structures, most noticeably the
simultaneous existence of both attractive and repulsive fifth-forces. Such
small-scale features are expected to imprint possibly observable footprints on
nonlinear cosmic structures, that might provide a direct way to test the
scenario. In order to unveil such footprints, we have performed the first suite
of high-resolution N-body simulations of McDE cosmologies, covering the
coupling range $|\beta |\leq 1$. We find that for coupling values corresponding
to fifth-forces weaker than standard gravity, the impact on structure formation
is very mild, thereby showing a new type of screening mechanism for long-range
scalar interactions. On the contrary, for fifth-forces comparable to or
stronger than standard gravity a number of effects appear in the statistical
and structural properties of CDM halos. Collapsed structures start to fragment
into pairs of smaller objects that move on different trajectories, providing a
direct evidence of the violation of the weak equivalence principle.
Consequently, the relative abundance of halos of different masses is
significantly modified. For sufficiently large coupling values, the expected
number of clusters is strongly suppressed, which might alleviate the present
tension between CMB- and cluster-based cosmological constraints. Finally, the
internal structure of halos is also modified, with a significant suppression of
the inner overdensity, and a progressive segregation of the two CDM species.
