Transition magnetic-dipole dark matter and the LZ230616 high-recoil candidate

Abstract

A transition magnetic dipole connects an endothermic nuclear recoil to a delayed photon. We study this interpretation of LZ230616, the 248-keV candidate in LZ's extended-energy search. Imposing the thermal abundance in a point hypercharge theory fixes a moment near $2.4 \times 10^{-4} \mathrm{TeV}^{-1}$ at the preferred masses, leaving a mass--splitting fit. The excited state travels about 0.6 m, making its decay relevant to the isolated-recoil selection. A position-dependent TPC-exit response gives conditional maxima at $(1.07 \,\mathrm{TeV} ,346 \,\mathrm{keV} )$ without the high-energy sideband and $(0.44 \,\mathrm{TeV} ,321 \,\mathrm{keV})$ with its zero-count proxy. Their line rates exceed the H.E.S.S. Einasto bound by factors of about 11 and 5.5. We examine halo dependence, other direct and indirect probes, and charged-messenger matching. Allowing a smaller moment and additional annihilation preserves the low-mass maxima while admitting heavier fits over 0.1--100 TeV. Delayed recoil--photon data can measure the splitting and moment, testing both the detector response and the assumed connection to thermal annihilation.