Dark matter and observable Lepton Flavour Violation
  Seesaw models with leptonic symmetries allow right-handed (RH) neutrino
masses at the electroweak scale, or even lower, at the same time having large
Yukawa couplings with the Standard Model leptons, thus yielding observable
effects at current or near-future lepton-flavour-violation (LFV) experiments.
These models have been previously considered also in connection to low-scale
leptogenesis, but the combination of observable LFV and successful leptogenesis
has appeared to be difficult to achieve unless the leptonic symmetry is
embedded into a larger one. In this paper, instead, we follow a different route
and consider a possible connection between large LFV rates and Dark Matter
(DM). We present a model in which the same leptonic symmetry responsible for
the large Yukawa couplings guarantees the stability of the DM candidate,
identified as the lightest of the RH neutrinos. The spontaneous breaking of
this symmetry, caused by a Majoron-like field, also provides a mechanism to
produce the observed relic density via the decays of the latter. The
phenomenological implications of the model are discussed, finding that large
LFV rates, observable in the near-future $\mu \to e$ conversion experiments,
require the DM mass to be in the keV range. Moreover, the active-neutrino
coupling to the Majoron-like scalar field could be probed in future detections
of supernova neutrino bursts.
