More about Neutron Majorana mass from Exotic Instantons: an alternative mechanism in Low-Scale String theory

Abstract: We discuss an alternative for Baryon-violating six quarks transitions, in the contest of low scale string theory. In particular, with $M_{S}=10\div 10^{3}\rm TeV$, such a transition can be mediated by two color-triplets,through a quartic coupling with down-quarks,generated by exotic instantons, in a calculable and controllable way. We show how FCNCs limits on color-triplet massare well compatible with $n-\bar{n}$ oscillation ones. If a $n-\bar{n}$ transition were found, this would be an indirect hint for our model. This would strongly motivate researches of direct channels in proton-proton colliders. In fact, our model can be directly tested in a experimentally challenging $100\div 1000\, \rm TeV$ proton-proton collider, searching for our desired color-triplet states and an evidence for exotic instantons resonances, in addition to stringy Regge resonances, anomalous $Z'$-bosons and gauged megaxion. In particular, our scenario can be related to the $750\, \rm GeV$ diphoton hint identifying it with the gauged megaxion dual to the $B$-field. On the other hand, this scenario is compatible with TeV-ish color triplets visible at LHC and with $1\div 10\, \rm TeV$- string scale, {\it i.e} stringy resonances at LHC.