Ultralight dark matter search in a large liquid scintillator detector

TL;DR

Ultralight scalar dark matter (ULDM) that couples to active neutrinos can induce time-averaged modulations in neutrino mass-squared differences, effectively smearing oscillation probabilities when the ULDM oscillation period is short compared with the experiment. The authors analyze a JUNO-like large liquid scintillator detector with a GLoBES-based simulation, introducing the parameters $\eta_{\Delta_{21}}$ and $\eta_{\Delta_{31}}$ to describe ULDM-induced fractional shifts $\Delta\hat{m}^2_{jk}=\Delta m^2_{jk}[1+2\eta_{\Delta_{jk}}\sin(m_{\phi} t)]$, and perform a likelihood analysis including priors on standard oscillation parameters. They project 90% CL bounds of $\eta_{\Delta_{21}} \lesssim 2.5\times10^{-2}$ and $\eta_{\Delta_{31}} \lesssim 5\times10^{-3}$, translating to Yukawa couplings $\hat{y}_{21}$ and $\hat{y}_{31}$ at the $\sim\text{a few}\times10^{-22}$ level for representative ULDM densities; ULDM effects produce mild correlations with $\Delta m^2_{21}$ and $\Delta m^2_{31}$ and can modestly degrade the precision of $\sin^2\theta_{13}$ and the mass-ordering sensitivity. These findings highlight the potential of upcoming large-volume detectors to probe neutrino-ULDM interactions via oscillation phenomenology and motivate incorporating ULDM effects and more detailed detector systematics in future precision studies.

Abstract

The nature of dark matter remains one of the most profound mysteries in modern physics. In this work, we investigate the phenomenological implications of ultralight scalar dark matter (ULDM) coupled to neutrinos. We focus on a large homogeneous liquid scintillator detector, analyzing the regime where ULDM oscillations lead to time-averaged distortions in neutrino oscillation probabilities. We derive sensitivity limits on the modulation parameters $η_{Δ_{21}}$ and $η_{Δ_{31}}$, which quantify ULDM-induced smearing effect in oscillations driven by solar ($Δm^2_{21}$) and atmospheric ($Δm^2_{31}$) mass-squared differences. We further demonstrate that ULDM interactions could produce a mild impact on both the determinations of the neutrino oscillation parameters and the neutrino mass ordering sensitivity. These results showcase the benefits of a large liquid scintillator detector as a powerful probe of neutrino-ULDM interactions via neutrino oscillations.

Figures (6)

• Figure 1: Reconstructed spectra at the JUNO-like setup. The blue solid line represents the spectrum within the standard three-neutrino ($3\nu$) oscillation framework. The green dashed line shows the expected background. The red and (brown) dashed lines represent the spectra including ultralight scalar field effects assuming $\eta_{\Delta_{31}} = 0.01$ and ($\eta_{\Delta_{21}} = 0.03$), respectively. See the text for a detailed explanation.
• Figure 2: Projected $\Delta \chi^2$ sensitivity to the ultralight scalar field parameters $\eta_{\Delta_{21}}$ (left panel) and $\eta_{\Delta_{31}}$ (right panel) from mass-squared modulations at the JUNO-like configuration. See the text for a detailed explanation.
• Figure 3: Limits and sensitivity regions in the $\hat{y}-m_\phi$ plane. The black dashed line represents the excluded limits from the CMB measurements on the total sum of the neutrino masses Planck:2018vyg. In the brown-shaded region, ultralight scalar dark matter lighter than $m_\phi \sim 10^{-21}\ \mathrm{eV}$ is in tension with Lyman-$\alpha$ forest observations Berlin:2016woy. Furthermore, solid lines indicate the expected sensitivities for the neutrino--ultralight dark matter scenario via time-averaged modulations from the JUNO-like setup (this work), DUNE Dev:2020kgz, and ESSnuSB Cordero:2022fwb, along with current constraints from solar neutrino measurements (Super-K and SNO) Berlin:2016woy. Here, these limits were derived under the assumption that ultralight dark matter constitutes 10% of the total dark matter abundance.
• Figure 4: Correlations among the ultralight scalar field parameters $\eta_{\Delta_{21}}$ ($\eta_{\Delta_{31}}$) from the corresponding solar (atmospheric) mass-squared modulations. Contours enclosed by the dashed, solid, and dot-dashed lines denote the $1\sigma$, $2\sigma$, and $3\sigma$ sensitivity regions, accordingly. See the text for a detailed explanation.
• Figure 5: Impact of ultralight scalar field parameters $\eta_{\Delta_{jk}}$ on the determination of oscillation parameters: $\sin^2\theta_{12}$ vs. $\Delta m^2_{21}$ (left panel) and $\sin^2\theta_{13}$ vs. $\Delta m^2_{31}$ (right panel). The standard three-neutrino scenario (SM) serves as reference. Green and purple lines show the effect when $\eta_{\Delta_{jk}}$ parameters are included in both simulation input and fit (SM + $\eta_{\Delta_{jk}}$). Input values were fixed to $\eta_{\Delta_{21}} = 2 \times 10^{-2}$, and $\eta_{\Delta_{31}} = 5 \times 10^{-3}$, accordingly. See the text for a detailed explanation.