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PreprintCC BY 4.0arXiv

Constraining U(1)Lμ−Lτ Model with Dark Matter Using Relic Density and Neff Bounds

  • Shivam Gola
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Abstract

We study thermal Dirac dark matter in the gauged U(1)Lμ−Lτ model, focusing on resonant annihilation near the Z' pole. We determine the parameter space that satisfies the Planck relic density bound while remaining consistent with collider, astrophysical, and laboratory searches. MeV-scale dark matter and the Z' mediator decouple near the active neutrino decoupling temperature; entropy injection into the neutrino bath modifies Tν/Tγ, leading to a shift in the effective number of relativistic species, Neff. Incorporating the coupled temperature evolution alongside the Planck 2018 limit on Neff, we find that the viable parameter space is restricted to a narrow mass window of MZ' ∼ 30−−50 MeV with g' ≃ 10−7−10−6, well within reach of upcoming fixed-target experiments such as SHiP and LDMX.

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Cite

BibTeXRIS
BibTeX
@misc{gola2026constraining,
  title = {{Constraining $U(1)_L_μ-L_τ$ Model with Dark Matter Using Relic Density and $N_\rm eff$ Bounds}},
  author = {Shivam Gola},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2611.07031},
  eprint = {2611.07031},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2611.07031},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Constraining U(1)_L_μ−L_τ Model with Dark Matter Using Relic Density and N_eff Bounds
AU  - Shivam Gola
PY  - 2026
DA  - 2026/11/04
PB  - arXiv
DO  - 10.48550/arxiv.2611.07031
UR  - https://arxiv.org/abs/2611.07031
AB  - We study thermal Dirac dark matter in the gauged U(1)_L_μ−L_τ model, focusing on resonant annihilation near the Z' pole. We determine the parameter space that satisfies the Planck relic density bound while remaining consistent with collider, astrophysical, and laboratory searches. MeV-scale dark matter and the Z' mediator decouple near the active neutrino decoupling temperature; entropy injection into the neutrino bath modifies T_ν/T_γ, leading to a shift in the effective number of relativistic species, N_eff. Incorporating the coupled temperature evolution alongside the Planck 2018 limit on N_eff, we find that the viable parameter space is restricted to a narrow mass window of M_Z' ∼ 30−−50 MeV with g' ≃ 10^−7−10^−6, well within reach of upcoming fixed-target experiments such as SHiP and LDMX.
ER  -