Inelastic Scalar Dark Matter in a Gauged U(1)B-L Model and its LZ Phenomenology

We study inelastic scalar dark matter (DM) in a gauged U(1)B-L model motivated by the high-energy recoil candidate reported by LUX-ZEPLIN (LZ). The model introduces two complex scalars, $Φ$ and S, charged under U(1)B-L. The scalar S is responsible for spontaneous symmetry breaking, while the two real components of $Φ$, ϕ₁ and ϕ₂, serve as DM. This two-component DM framework accommodates both exothermic and endothermic scenarios. In the exothermic scenario, the lifetime of the heavier state ϕ₁ exceeds the age of the Universe, and both states contribute to the present-day DM abundance. In the endothermic scenario, the abundance comes almost entirely from the lighter state ϕ₂. We investigate the thermal history of the dark sector and find that the two scalars have approximately equal abundances at freeze-out. We identify parameter regions that reproduce the observed relic abundance. We calculate the nuclear recoil spectra, perform a three-bin likelihood analysis, and obtain the best-fit points interpreting the LZ signal in both scenarios.