Un-oriented Quiver Theories for Majorana Neutrons

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-\bar{n} limits. Finally we briefly comment on Pati-Salam extensions of our models.Comment: More comments on phenomenology and fluxes, Re-discussion of SM-quivers compatible with n-cycles conditions Version accepted by JHE

Neutron Majorana mass from exotic instantons

We show how a Majorana mass for the Neutron could result from non-perturbative quantum gravity effects peculiar to string theory. In particular, "exotic instantons" in un-oriented string compactifications with D-branes extending the (supersymmetric) standard model could indirectly produce an effective operator delta{m} n^t n+h.c. In a specific model with an extra vector-like pair of `quarks', acquiring a large mass proportional to the string mass scale (exponentially suppressed by a function of the string moduli fields), delta{m} can turn out to be as low as 10^{-24}-10^{-25} eV. The induced neutron-antineutron oscillations could take place with a time scale tau_{n\bar{n}} > 10^8 s, that could be tested by the next generation of experiments. On the other hand, proton decay and FCNC's are automatically strongly suppressed and are compatible with the current experimental limits. Depending on the number of brane intersections, the model may also lead to the generation of Majorana masses for R-handed neutrini. Our proposal could also suggest neutron-neutralino or neutron-axino oscillations, with implications in UCN, Dark Matter Direct Detection, UHECR and Neutron-Antineutron oscillations. This suggests to improve the limits on neutron-antineutron oscillations, as a possible test of string theory and quantum gravity.Comment: 35 pages, 11 figures. More comments on neutron-neutralino mixin

Towards a new Liquid Argon Imaging Chamber for the MODULAr project

The MODULAr project foresees the exploitation of a new liquid Argon imaging detector, of at least 20 kt fiducial mass, to be operated in a shallow depth location under the Gran Sasso Mountain. It will be devoted to study neutrino oscillations with an optimized off-axis CNGS neutrino beam. Cosmic neutrinos as well as proton decay will also be addressed. The MODULAr detector will vastly inherit from the technology developed for ICARUS-T600. However, such an increase in the volume over the current ICARUS-T600 needs to be carefully considered. It is concluded that a single, huge volume is an inoperable and uneconomical solution for many reasons. A very large mass is best realized with a modular set of many identical, independent units, each of about 5 kt, “cloning” the basic technology of the ICARUS-T600. Several of such modular units will be assembled to reach at least 20 kt as initial sensitive volume. The increase of the active volume of about one order of magnitude with respect to the ICARUS-T600 detector requires some specific R&D activity, which will be implemented in a ∼ 360 ton prototype unit (SLICE) of reduced length