Un-oriented quiver theories for Majorana neutrons

Abstract

In the context of un-oriented open string theories, we identify quivers whereby a Majorana mass for the neutron is indirectly generated by exotic instantons. We discuss two classes of (Susy) Standard Model like quivers, depending on the embedding of SU(2) W in the Chan-Paton group. In both cases, the main mechanism involves a vector-like pair mixing through a non-perturbative mass term. We also discuss possible relations between the phenomenology of Neutron-Antineutron oscillations and LHC physics in these models. In particular, a vector-like pair of color-triplet scalars or color-triplet fermions could be directly detected at LHC, compatibly with n −n limits. Finally we briefly comment on Pati-Salam extensions of our models.

‘Exotic vector-like pair’ of color-triplet scalars

“…9 Finally, we would like to remark that, an exotic mass term (5.3) cannot be introduced by-hand, at perturbative level, because of R-parity, i.e R-parity is dynamically broken, without the generation of other dangerous R-parity violating operators, as explained in [28,29,66].…”

“…In a broad sense, we have a seesaw mechanism for neutron, involving a non-diagonal mass matrix for scalars rather than fermions. 2,3 This model is inspired by proposals in [28,29,[53][54][55][56]: (NMS-)SM is obtained as a low energy limit of open (un)-oriented strings, attached between D-brane stacks and Euclidean D-branes. Euclidean D-branes are exotic stringy instantons, that can induce new non-perturbative mass terms, violating vector-like U(1)s, rather than axial-ones.…”

“…Euclidean D-branes are exotic stringy instantons, that can induce new non-perturbative mass terms, violating vector-like U(1)s, rather than axial-ones. In particular, in [28,29], R-parity is dynamically broken by exotic instantons, producing only particular B-violating operators, such as a mass term for a vector-like pair Proton decay is automatically suppressed in this model [28,29].…”

Neutron-antineutron transitions from exotic instantons: How fast they might be and further implications

“…In particular, we have suggested several explicit models generating a Majorana mass for the neutron. [1][2][3][4][5][6][7][8][9] Such a signature can be tested in the next generation of experiments in neutron-antineutron physics improving the present limit of τ 3 yrs (in vacuum), up to τ 300 yrs.…”

“…However, in string theory, they can be cured through a generalized Green-Schwarz mechanism if the number of intersections among D6-branes' stacks satisfy certain conditions for stringy tadpoles' cancellations, as happen in quiver Fig.1-(b). 3 This mechanism necessary involves extra Generalized Chern-Simons terms, mixing at tree level the anomalous Z , Z , associated with anomalous U (1) …”