The 3-3-1 Model: a natural framework for sub-MeV dark matter

We show that the $\mathrm{S}\mathrm{U}(3{)}_C\times \mathrm{S}\mathrm{U}(3{)}_L\times \mathrm{U}(1{)}_N$ model with right-handed neutrinos naturally accommodates a viable sub-MeV dark matter (DM) candidate realized as pseudo-Goldstone boson that acquires tiny mass through gravitational effects. The observed relic abundance is obtained via freeze-in in a low-reheating temperature scenario, without requiring tiny couplings. The model operates at the TeV scale and remains testable at current and future collider experiments.