  We show how exotic stringy instantons can generate an effective interaction
between color diquark sextets in a Pati-Salam model, inducing a Majorana mass
term for the neutron. In particular, we discuss a simple quiver theory for a
Pati-Salam like model, as an example in which the calculations of exotic
instantons' effects are simple and controllable. We discuss some different
possibilities in order to generate $n-\bar{n}$ oscillation testable in the next
generation of experiments, Majorana mass matrices for neutrini and a
Post-Sphaleron Baryogenesis scenario. Connections with Dark Matter issues and
the Higgs mass Hierarchy problem are discussed, in view of implications for LHC
and rare processes physics. The model may be viewed as a completion of
Left-Right symmetry, alternative to a GUT-inspired scenario. Combined measures
in Neutron-Antineutron physics, FCNC, LHC, Dark Matter could rule out the
proposed model or uncover aspects of physics at the Planck scale!
