Neutron Majorana mass from exotic instantons in a Pati-Salam model

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 instanton effects are simple and controllable. We discuss some different possibilities in order to generate n - n oscillations 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 a Left-Right symmetric extension of the Standard Model, 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!.