From Dirac Neutrino Mass to Dark Radiation: An A4-Symmetric FIMP Dark Matter Framework
Abstract
We propose a unified A4× Z2× U(1)L framework for generating small Dirac neutrino masses and address dark matter through feeble interactions in an extended particle physics model. The model extends the Standard Model with a pair of heavy vector-like neutral A4 fermions N(NL,R), two additional flavon fields η and ϕ, among which η being a Z2-odd inert scalar and a dark-sector vector-like fermion field χ. We numerically explore the Dirac-sector Yukawa couplings and identify the parameter region that is consistent with the {\tt NuFit 6.1} neutrino oscillation data at the 3σ level. The dark matter candidate χ, stabilized by the Z2 symmetry, is produced non-thermally through the decay NL→χ+η. By solving the Boltzmann equation, we find that the observed relic abundance, ΩDMh2≃0.12, can be reproduced for freeze-in couplings of order λ∼10−5.5--10−7.5 over the considered dark matter mass range. For the chosen parameter space, we also verify the interaction rate remains below the Hubble expansion rate, confirming χ never reaches thermal equilibrium. Thus, our results demonstrate that the model provides a consistent realization of Dirac neutrino masses and FIMP dark matter within a common symmetry-based setup. The presence of light Dirac RH neutrinos can contribute to the dark radiation and hence the effective degrees of freedom via thermal and non-thermal processes. We further estimate the contribution of the light right-handed neutrinos to ΔNeff, finding a maximum characteristic value of ΔNeff≃0.14 in the benchmark parameter region.
Related
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BibTeX
@misc{das2026from,
title = {{From Dirac Neutrino Mass to Dark Radiation: An $A_4$-Symmetric FIMP Dark Matter Framework}},
author = {Pritam Das and Anupam Deka and Debajyoti Dutta},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15618},
eprint = {2610.15618},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15618},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - From Dirac Neutrino Mass to Dark Radiation: An A_4-Symmetric FIMP Dark Matter Framework
AU - Pritam Das
AU - Anupam Deka
AU - Debajyoti Dutta
PY - 2026
DA - 2026/10/11
PB - arXiv
DO - 10.48550/arxiv.2610.15618
UR - https://arxiv.org/abs/2610.15618
AB - We propose a unified A_4× Z_2× U(1)_L framework for generating small Dirac neutrino masses and address dark matter through feeble interactions in an extended particle physics model. The model extends the Standard Model with a pair of heavy vector-like neutral A_4 fermions N(N_L,R), two additional flavon fields η and ϕ, among which η being a Z_2-odd inert scalar and a dark-sector vector-like fermion field χ. We numerically explore the Dirac-sector Yukawa couplings and identify the parameter region that is consistent with the {\tt NuFit 6.1} neutrino oscillation data at the 3σ level. The dark matter candidate χ, stabilized by the Z_2 symmetry, is produced non-thermally through the decay N_L→χ+η. By solving the Boltzmann equation, we find that the observed relic abundance, Ω_DMh^2≃0.12, can be reproduced for freeze-in couplings of order λ∼10^−5.5--10^−7.5 over the considered dark matter mass range. For the chosen parameter space, we also verify the interaction rate remains below the Hubble expansion rate, confirming χ never reaches thermal equilibrium. Thus, our results demonstrate that the model provides a consistent realization of Dirac neutrino masses and FIMP dark matter within a common symmetry-based setup. The presence of light Dirac RH neutrinos can contribute to the dark radiation and hence the effective degrees of freedom via thermal and non-thermal processes. We further estimate the contribution of the light right-handed neutrinos to ΔN_eff, finding a maximum characteristic value of ΔN_eff≃0.14 in the benchmark parameter region.
ER -