Investigating DUNE oscillations sensitivity to sterile pseudo-Dirac neutrinos

We explore the sensitivity of the Deep Underground Neutrino Experiment (DUNE) to sterile neutrino oscillations within a 3+(pseudo-Dirac pair) framework. We first consider a pair of two sterile neutrinos forming a pseudo-Dirac pair, then we consider a low-scale seesaw realization, that we name “Linear-Inverse Seesaw” model. This scenario features two nearly degenerate sterile neutrino states at the keV scale, characterized by a small mass splitting arising from a small amount of lepton number violation. In this scenario, the oscillation behavior can be described in three distinct regimes depending on the sterile-sterile mass-squared difference: low (< 1 eV2), resonant (1–100 eV2), and high (> 100 eV2) regimes, recovering in both low- and high-mass regimes an effective non-unitarity of the leptonic mixing matrix. A distinctive feature of this framework is that observable effects persist even in the low-mass limit, unlike the case of standard 3 +1 scenarios, due to rapid oscillation averaging from larger keV-scale splittings. We leverage the complementarity of both near and far detectors to explore the sensitivity to νe and νμ disappearance and νe and ντ appearance oscillation probabilities. Our analysis reveals that DUNE can achieve significant improvements over current experimental constraints, especially in neutrino appearance modes. Additionally, we show that new CP-violating phases associated with the sterile sector can dramatically alter the sensitivity, with destructive interference potentially suppressing signals by orders of magnitude.