Mixed Freeze-In and Freeze-Out Histories and Dark-Sector Decays in a $\mathbb{Z}_4$ Two-Scalar Model
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| Format: | Preprint |
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2026
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| author | Carvalho-Corrêa, J. P. Silva, B. A. Couto e Sánchez-Vega, B. L. |
| author_facet | Carvalho-Corrêa, J. P. Silva, B. A. Couto e Sánchez-Vega, B. L. |
| contents | We present a systematic non-equilibrium analysis of a renormalisable $\mathbb{Z}_4$ Higgs-portal dark sector comprising a complex scalar $S_A$ and a real scalar $S_B$. In this framework, conversion, semi-annihilation, and (when kinematically allowed) $S_B\to S_A S_A$ decays shape the coupled relic-density evolution. Imposing theoretical consistency, Higgs invisible-decay limits, and the latest LZ spin-independent bound with the standard relic-fraction rescaling, we show that the severe exclusions typical of thermal two-WIMP analyses are largely an artefact of requiring both components to thermalise with the SM bath. Mixed WIMP-FIMP (and fully feeble FIMP-FIMP) histories reopen regions excluded in thermal two-WIMP interpretations, since the total relic density can be shared while the direct-detection signal is carried only by the thermal fraction. For the unstable hierarchy $M_{S_B}>2M_{S_A}$, we identify decay-dominated regimes-SuperWIMP, injection-assisted freeze-out, and sequential freeze-in (``SuperFIMP'')-where late dark-sector injection sets the final $S_A$ abundance. These results establish the $\mathbb{Z}_4$ Higgs-portal model as a controlled benchmark for multi-component dark matter beyond the two-thermal-relic assumption. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_18564 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Mixed Freeze-In and Freeze-Out Histories and Dark-Sector Decays in a $\mathbb{Z}_4$ Two-Scalar Model Carvalho-Corrêa, J. P. Silva, B. A. Couto e Sánchez-Vega, B. L. High Energy Physics - Phenomenology High Energy Physics - Theory We present a systematic non-equilibrium analysis of a renormalisable $\mathbb{Z}_4$ Higgs-portal dark sector comprising a complex scalar $S_A$ and a real scalar $S_B$. In this framework, conversion, semi-annihilation, and (when kinematically allowed) $S_B\to S_A S_A$ decays shape the coupled relic-density evolution. Imposing theoretical consistency, Higgs invisible-decay limits, and the latest LZ spin-independent bound with the standard relic-fraction rescaling, we show that the severe exclusions typical of thermal two-WIMP analyses are largely an artefact of requiring both components to thermalise with the SM bath. Mixed WIMP-FIMP (and fully feeble FIMP-FIMP) histories reopen regions excluded in thermal two-WIMP interpretations, since the total relic density can be shared while the direct-detection signal is carried only by the thermal fraction. For the unstable hierarchy $M_{S_B}>2M_{S_A}$, we identify decay-dominated regimes-SuperWIMP, injection-assisted freeze-out, and sequential freeze-in (``SuperFIMP'')-where late dark-sector injection sets the final $S_A$ abundance. These results establish the $\mathbb{Z}_4$ Higgs-portal model as a controlled benchmark for multi-component dark matter beyond the two-thermal-relic assumption. |
| title | Mixed Freeze-In and Freeze-Out Histories and Dark-Sector Decays in a $\mathbb{Z}_4$ Two-Scalar Model |
| topic | High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2602.18564 |