Inelastic Dark Matter at LZ from Radiative Dirac Neutrino Mass Paradigm

The LUX-ZEPLIN (LZ) experiment has reported a high-energy nuclear recoil candidate, LZ230616, at E R = 248 plus or minus 23 stat plus or minus 23 sys, keV, which is difficult to reconcile with elastic scattering of halo dark matter (DM). Endothermic inelastic scattering offers a natural explanation, but it rests on a nucleon coupling that is off-diagonal rather than diagonal. We show that this feature arises automatically within a radiative Dirac neutrino mass framework. The Standard Model is extended by three right-handed neutrinos (RHNs), a pair of vector-like neutral fermions for each generations, and a scalar sector comprising an inert doublet and a real singlet, governed by a Z 2 times Z 4 symmetry. The Z 2 symmetry stabilizes the DM, while the Z 4 symmetry forbids the tree-level Dirac Yukawa coupling together with all renormalizable Majorana mass terms, thereby allowing the generation of Dirac neutrino masses at the one-loop level through a softly broken scalar trilinear coupling ` κ '. Since the neutral dark-sector fields can be expressed in terms of real scalar mass eigenstates, the Z boson couples to them purely off-diagonally and elastic Z-mediated scattering is absent identically rather than simply suppressed. The singlet--doublet mixing induced by ` κ ' governs both the inelastic rate and the one-loop Dirac neutrino mass, which therefore vanish as κ to 0. We find that DM masses in the few hundred GeV to TeV range, with splittings of O(340-360), keV, simultaneously reproduce the observed relic abundance, account for the LZ event and yield neutrino masses of the correct order, while respecting elastic direct-detection limits and all relevant theoretical and experimental constraints. A substantial part of the surviving parameter space lies within reach of DARWIN.