Parametric resonance in neutrino oscillations induced by ultra-light dark matter and implications for KamLAND and JUNO

If ultra-light dark matter (ULDM) exists and couples to neutrinos, the neutrino oscillation probability might be significantly altered by a parametric resonance. This resonance can occur if the typical frequency of neutrino flavor-oscillations $Δm^2/(2E)$, where $Δm^2$ is the mass-squared difference of the neutrinos and $E$ is the neutrino energy, matches the oscillation frequency of the ULDM field, determined by its mass, $m_φ$. The resonance could lead to observable effects even if the ULDM coupling is very small, and even if its typical oscillation period, given by $τ_φ=2π/m_φ$, is much shorter than the experimental temporal resolution. Defining a small parameter $ε_φ$ to be the ratio between the contribution of the ULDM field to the neutrino mass and the vacuum value of the neutrino mass, the impact of the resonance is particularly significant if $ε_φm_φL\gtrsim 4$, where $L$ is the distance between the neutrino source and the detector. Such parametric resonance can improve the fit to the KamLAND experiment measurements by about $3.5\,σ$ compared to standard oscillations. This scenario will be tested by the JUNO experiment.