New Avenues for |ΔB=2| Processes Beyond Neutron-Antineutron Oscillations

We explore baryon-number-violating (|∆B| = 2) processes beyond the well-known neutron-antineutron (n-n̄) oscillations, focusing on the Λ-Λ̄ 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-n̄ 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-Λ̄ oscillations can occur at tree level, with n-n̄ mixing potentially appearing at higher loop levels. We employ a chiral effective theory to constrain the effective mass mixing δmΛ, deriving bounds from current experimental limits on n-n̄ oscillations and dinucleon decays such as pp → K+K+. These bounds indicate that Λ-Λ̄ oscillations probe a complementary parameter space, sensitive to baryon-number violation at scales up to 102 − 103 TeV. We show that the existing indirect bounds make it challenging to provide a competitive bound on δmΛ at BESIII.