Nested Disappearing-Track plus Displaced-Vertex Topology at the HL-LHC: A Dual Long-Lived-Particle Signature of the Scotogenic Model

The scotogenic model generates sub-eV neutrino masses radiatively through small Yukawa couplings $\sim\mathcal{O}(10^{-3})$ that also set the decay length of the heavy neutral fermion $\Ntwo$; in the compressed regime a separate, much smaller Yukawa entry $\sim\mathcal{O}(10^{-6})$ additionally rend