Abstract: We explore baryon-number-violating (|∆B| = 2) processes beyond the well-known neutron-antineutron (n−n‾) oscillations, focusing on the Λ−Λ‾ system. The presence of a strange quark in the Λ baryon introduces a new set of six-quark operators roughly of the form (uds)2, which are different from the (udd)2 operators responsible for n−n‾ oscillations. Using the Standard Model Effective Field Theory (SMEFT), we classify all dimension-9 operators that cause |∆B| = 2 transitions and study their UV completions mediated by exotic scalar fields with trilinear interactions. We demonstrate that in these models, Λ−Λ‾ oscillations can occur at tree level, with n−n‾ mixing potentially appearing at higher loop levels. We employ a chiral effective theory to constrain the effective mass mixing δmΛΛ​, deriving bounds from current experimental limits on n−n‾ oscillations and dinucleon decays such as pp → K+K+. These bounds indicate that Λ−Λ‾ oscillations probe a complementary parameter space, sensitive to baryon-number violation at scales up to 10^2 − 10^3 TeV. We show that the existing indirect bounds make it challenging to provide a competitive bound on δmΛΛ​ at BESIII.

Abstract: Baryon and lepton number are excellent low-energy symmetries of the Standard Model (SM) that tightly constrain the form of its extensions. In this paper we investigate the possibility that these accidental symmetries are violated in the deep UV, in such a way that one multiplet necessary for their violation lives at an intermediate energy scale M above the electroweak scale. We write down the simplest effective operators containing each multiplet that may couple linearly to the SM at the renormalisable level and estimate the dominant contribution of the underlying UV model to the pertinent operators in the SMEFT: the dimension-5 Weinberg operator and the baryon-number-violating operators up to dimension 7. Our results are upper bounds on the scale M for each multiplet-operator pair, derived from neutrino-oscillation data as well as prospective nucleon-decay searches. We also analyse the possibility that both processes are simultaneously explained within a natural UV model. In addition, we advocate that our framework provides a convenient and digestible way of organising the space of UV models that violate these symmetries.

Abstract: We investigate the potential of future neutrino experiments, DUNE and Hyper-Kamiokande, to probe magnetic monopoles via Callan-Rubakov (CR) processes. We consider both relativistic and non-relativistic monopoles and focus on two primary detection signatures: high-energy antiproton production and proton decay catalysis. For relativistic monopoles, our analysis of the CR process indicates antiproton production with energies near 900 GeV and we find that both experiments can provide limits on the fluxes an order of magnitude below the Parker bound (approximately Phi less than or similar to 10-16 cm-2 s-1 sr-1). For non-relativistic monopoles, we recast the experimental sensitivity to proton decay catalysis and obtain upper limits on the monopole flux of Phi less than or similar to 2.3 x 10-23 cm-2 s-1 sr-1 for Hyper-Kamiokande and Phi less than or similar to 1.1 x 10-22 cm-2 s-1 sr-1 for DUNE.