2026/02/28 by XinXin Qi, Hao Sun
Physics and Astronomy · #hep-ph
arxiv created 2026/07/30 · arxiv updated 2026/07/31
We study the freeze-in production of a two-component dark matter model with Z2× Z4 symmetry where a singlet scalar S and a Majorana fermion χ are the DM candidates. A singlet scalar S0 with a non-zero vev v0 generates χ's mass after spontaneous symmetry breaking. We choose six free parameters with the Higgs mixing angle fixed at sinθ=10-4 in this work. Depending on whether mχ and mS lie above or below m2/2, with m2 being the new Higgs h2 mass, we have four phenomenological cases with distinct production channels. For m2=1~TeV, we determine the viable parameter space consistent with the observed DM relic density by numerically solving the Boltzmann equations. Both DM masses are viable in the range [1~GeV, 3~TeV]. The coupling λds can reach O(10-25), roughly fifteen orders of magnitude below conventional FIMP values---a suppression that originates from the large hierarchy v0, which enhances h2-mediated S production and forces λds to be correspondingly tiny. Remarkably, h2 can still play a dominant role in determining S production even for such a tiny λds when mS<m2/2.