Constraining Ultra-Light Vector Bosons via Solar Neutrino Oscillations: The Gauged Lμ− Lτ Model and Prospects for JUNO and XLZD
Abstract
We present an extension of the Standard Model based upon the gauged U(1)Lμ− Lτ symmetry, featuring an ultra-light vector boson that couples to the difference of muon and tau lepton numbers. This anomaly-free construction, historically motivated by the muon's anomalous magnetic moment, is employed here as an independent phenomenological framework for solar neutrino physics. Through kinetic mixing with the photon, the Z′ boson generates an effective matter potential within the solar interior, thereby modifying neutrino flavour oscillations via the Mikheyev--Smirnov--Wolfenstein mechanism. Utilising recent solar neutrino measurements from Borexino, SNO, and Super-Kamiokande, together with an up-to-date standard solar model, we constrain the boson mass to be below 5.7× 10−17 eV, a potential ultra-light dark matter candidate. The optimal model, with coupling parameter ηo ≈ −2, yields χν2 = 2.7, compared with χν2 = 3.1 for the standard three-flavour scenario. This best fit corresponds to an effective four-fermion coupling gZ′2 ε / mZ′2 ≈ 6.6 × 10−23 eV−2, approximately $5.7$ times the Fermi constant, equivalent for ε ≈ 1 and a reference mediator mass of 1 eV to a gauge coupling gZ′ ≈ 8× 10−12. We also present projections for forthcoming experiments: the Jiangmen Underground Neutrino Observatory (JUNO), operating since August 2025 with world-leading precision on oscillation parameters, together with the XLZD consortium, should substantially refine these constraints. Such ultra-light particles may address long-standing discrepancies in galaxy simulations within the cold dark matter paradigm, whilst terrestrial long-baseline neutrino experiments provide complementary probes of this parameter space.
Versions
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BibTeX
@misc{lopes2026constraining,
title = {{Constraining Ultra-Light Vector Bosons via Solar Neutrino Oscillations: The Gauged $L_μ- L_τ$ Model and Prospects for JUNO and XLZD}},
author = {Ilídio Lopes},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.33877},
eprint = {2609.33877},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.33877},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Constraining Ultra-Light Vector Bosons via Solar Neutrino Oscillations: The Gauged L_μ− L_τ Model and Prospects for JUNO and XLZD
AU - Ilídio Lopes
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2609.33877
UR - https://arxiv.org/abs/2609.33877
AB - We present an extension of the Standard Model based upon the gauged U(1)_L_μ− L_τ symmetry, featuring an ultra-light vector boson that couples to the difference of muon and tau lepton numbers. This anomaly-free construction, historically motivated by the muon's anomalous magnetic moment, is employed here as an independent phenomenological framework for solar neutrino physics. Through kinetic mixing with the photon, the Z^′ boson generates an effective matter potential within the solar interior, thereby modifying neutrino flavour oscillations via the Mikheyev--Smirnov--Wolfenstein mechanism. Utilising recent solar neutrino measurements from Borexino, SNO, and Super-Kamiokande, together with an up-to-date standard solar model, we constrain the boson mass to be below 5.7× 10^−17 eV, a potential ultra-light dark matter candidate. The optimal model, with coupling parameter η_o ≈ −2, yields χ_ν^2 = 2.7, compared with χ_ν^2 = 3.1 for the standard three-flavour scenario. This best fit corresponds to an effective four-fermion coupling g_Z^′^2 ε / m_Z^′^2 ≈ 6.6 × 10^−23 eV^−2, approximately $5.7$ times the Fermi constant, equivalent for ε ≈ 1 and a reference mediator mass of 1 eV to a gauge coupling g_Z^′ ≈ 8× 10^−12. We also present projections for forthcoming experiments: the Jiangmen Underground Neutrino Observatory (JUNO), operating since August 2025 with world-leading precision on oscillation parameters, together with the XLZD consortium, should substantially refine these constraints. Such ultra-light particles may address long-standing discrepancies in galaxy simulations within the cold dark matter paradigm, whilst terrestrial long-baseline neutrino experiments provide complementary probes of this parameter space.
ER -