  At the Deep Underground Neutrino Experiment (DUNE), a proton beam hits a
fixed target leading to large production rates of mesons. These mesons can
decay and potentially provide a source of long-lived neutral fermions. Examples
of such long-lived fermions are heavy neutral leptons which can mix with the
standard-model active neutrinos, and the bino-like lightest neutralino in
R-parity-violating supersymmetry. We show that the Standard Model Effective
Field Theory extended with right-handed singlet neutrinos can simultaneously
describe heavy neutral leptons and bino-like neutralinos in a unified manner.
We use the effective-field-theory framework to determine the sensitivity reach
of the DUNE near detector in probing various scenarios of long-lived neutral
fermions.
