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arXiv · 2512.05694

Nearly Degenerate Majorana Dark Matter and Its Self-Interactions in a Gauged $U(1)_{L_\mu - L_\tau}$ Model

Kwei-Chou Yang
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Abstract

We propose a model of nearly degenerate Majorana dark matter (DM) in a gauged $U(1)_{L_\mu - L_\tau}$ extension of the Standard Model. Spontaneous symmetry breaking generates a dominant Majorana mass via a strong Yukawa coupling, splitting the dark fermion into two nearly degenerate states. The lighter state ($\chi_-$) is the DM candidate, with an allowed mass of $\sim 10$ GeV to several hundred GeV. Crucially, within the $10 \sim 75$ GeV mass range and a scalar mediator at the tens of MeV scale, this strong coupling dictates the thermal relic abundance and induces significant elastic self-interactions. These self-interactions naturally resolve small-scale structure anomalies, such as the core-cusp problem, while satisfying massive cluster constraints. Furthermore, we place stringent joint constraints on the scalar mass and the Higgs mixing angle $\alpha$ using the latest LZ 2025 direct detection data. The model's gauge boson $Z^\prime$ maintains early-Universe thermal equilibrium and accommodates the muon anomalous magnetic moment $(g-2)_\mu$, remaining consistent with updated cosmological and experimental bounds.

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Kwei-Chou Yang. 2025-12-05. Nearly Degenerate Majorana Dark Matter and Its Self-Interactions in a Gauged $U(1)_{L_\mu - L_\tau}$ Model. https://arxiv.org/abs/2512.05694

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