Freeze-in of anapole and charge-radius inelastic dark matter: X-ray probes of a decoupled vector portal
Abstract
We study freeze-in production and experimental probes of inelastic dark matter (iDM) coupled to the Standard Model through dimension-6 transition anapole and charge-radius operators. These interactions arise upon integrating out the heavy dark photon of a broken U(1)D vector portal. We focus on mass splittings below the dielectron threshold, where the excited-state decay is cosmologically long-lived and decays predominantly through χ1→χ0+3γ, producing a distinctive keV--MeV photon spectrum. We calculate the decay rate and photon spectrum analytically in the Euler--Heisenberg limit and evaluate finite-electron-mass corrections using the full one-loop amplitude. We then combine X-ray limits with freeze-in relic density targets and complementary direct detection (DD) and accelerator constraints. The surviving χ1 population also leads to exothermic downscattering signatures at DD experiments, including the possibility of explaining the LZ signal, while the three-photon decay is constrained by X-ray data. At Δ=900 keV, INTEGRAL/SPI probes the Boltzmann-suppressed high-mass branches of the freeze-in targets, whereas the NuSTAR limits at Δ=100 keV are substantially weaker because of the steep splitting dependence of the decay width. Our results demonstrate the potential of X-ray observations as a probe of freeze-in through a decoupled vector portal and of the reheating temperature governing the iDM production.
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BibTeX
@misc{jodlowski2026freezein,
title = {{Freeze-in of anapole and charge-radius inelastic dark matter: X-ray probes of a decoupled vector portal}},
author = {Krzysztof Jodłowski and Chih-Ting Lu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.34230},
eprint = {2609.34230},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.34230},
}
RIS
TY - UNPB
TI - Freeze-in of anapole and charge-radius inelastic dark matter: X-ray probes of a decoupled vector portal
AU - Krzysztof Jodłowski
AU - Chih-Ting Lu
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.34230
UR - https://arxiv.org/abs/2609.34230
AB - We study freeze-in production and experimental probes of inelastic dark matter (iDM) coupled to the Standard Model through dimension-6 transition anapole and charge-radius operators. These interactions arise upon integrating out the heavy dark photon of a broken U(1)_D vector portal. We focus on mass splittings below the dielectron threshold, where the excited-state decay is cosmologically long-lived and decays predominantly through χ_1→χ_0+3γ, producing a distinctive keV--MeV photon spectrum. We calculate the decay rate and photon spectrum analytically in the Euler--Heisenberg limit and evaluate finite-electron-mass corrections using the full one-loop amplitude. We then combine X-ray limits with freeze-in relic density targets and complementary direct detection (DD) and accelerator constraints. The surviving χ_1 population also leads to exothermic downscattering signatures at DD experiments, including the possibility of explaining the LZ signal, while the three-photon decay is constrained by X-ray data. At Δ=900 keV, INTEGRAL/SPI probes the Boltzmann-suppressed high-mass branches of the freeze-in targets, whereas the NuSTAR limits at Δ=100 keV are substantially weaker because of the steep splitting dependence of the decay width. Our results demonstrate the potential of X-ray observations as a probe of freeze-in through a decoupled vector portal and of the reheating temperature governing the iDM production.
ER -