JUNO's Impact on the Neutrino Mass Ordering from Lorentz Invariance Violation

TL;DR

This work probes Lorentz invariance violation (LIV) in neutrino oscillations using JUNO's 59.1-day reactor antineutrino dataset, parameterizing LIV through CPT-even ($c_{ee}-c_{e\mu}$, $c_{ee}-c_{e\tau}$) and CPT-odd ($a_{ee}-a_{e\mu}$, $a_{ee}-a_{e\tau}$) coefficients within the Standard-Model Extension. The authors perform a GLoBES-based analysis that incorporates the LIV Hamiltonian, marginalizes over standard oscillation parameters, and reports competitive 3$\sigma$ bounds: $c_{ee}\lesssim 1.0\times10^{-18}$, $c_{e\tau}\lesssim 2.7\times10^{-19}$, $c_{e\mu}\lesssim 2.0\times10^{-19}$ (CPT-even) and $a_{ee}\lesssim 2.2\times10^{-12}$ GeV, $a_{e\mu}\lesssim 8.0\times10^{-13}$ GeV, $a_{e\tau}\lesssim 6\times10^{-13}$ GeV (CPT-odd). Remarkably, including the best-fit LIV values reshapes the solar-oscillation parameter space, driving NO toward higher $\sin^2\theta_{12}$ and strengthening IO’s relative preference (about 3$\sigma$) in the $\sin^2\theta_{12}-\Delta m^2_{21}$ plane. The results demonstrate JUNO’s sensitivity to subleading LIV effects and provide a baseline for future, larger datasets to further constrain Lorentz-violating scenarios and the neutrino mass ordering.

Abstract

We explore the potential of the Jiangmen Underground Neutrino Observatory (JUNO) to probe new physics by searching for Lorentz-invariance violation (LIV). Using the 59.1-day dataset recently released by this experiment, we analyze neutrino oscillations to place new constraints on the LIV parameters in the CPT-even ($c_{ee} - c_{eμ}$, $c_{ee} - c_{eτ}$) and CPT-odd ($a_{ee} - a_{eμ}$, $a_{ee} - a_{eτ}$) sectors. Our analysis reveals a significant shift in the oscillation parameter space of $\sin^2θ_{12}-Δm^2_{21}$ when LIV is included; with the best-fit point for normal ordering moving to the higher values of the solar angle $θ_{12}$, a strong preference emerges for inverted mass ordering. In particular, the $c_{ee} - c_{eτ}$ and $a_{ee} - a_{eτ}$ sectors show the most pronounced effects. We report the most stringent bounds from JUNO to date on these LIV parameters, showcasing the detector's unique sensitivity to physics beyond the Standard Model.

Figures (12)

• Figure 1: Left: Reconstructed JUNO prompt energy spectrum (per 0.1 MeV) from 59.1 day data set abusleme2025first. The blue curve shows the raw experimental data, while the red curve represents the data after subtracting all background components, shown individually as the green (geo-$\nu$), pink ($^{9}$Li/$^{8}$He), grey (world reactors), and light blue ($^{214}$Bi-$^{214}$Po) contributions. The black dotted curve represents the expected unoscillated reactor flux. Right: Unoscillated event rates from JUNO (black) compared with GLoBES simulations (dark blue). The events using the best-fit obtained using GLoBES prediction for standard oscillation for NO are shown in light blue. The experimental events after subtracting all the backgrounds from JUNO data (blue) are shown by the red curve in both panels. These comparisons validate the input used for the LIV sensitivity analysis.
• Figure 2: Total chi-square for $\sin^2\theta_{12}-\Delta m_{21}^2$ plane for NO (left) and IO (right). 1$\sigma$ and 3$\sigma$ contours are shown by green and blue lines, respectively, along with the best-fit point. This $\chi^2$ analysis was computed marginalizing on $\Delta m_{31}^2$ and $\theta_{13}$ parameters.
• Figure 3: Two dimensional $\Delta\chi^{2}$ contours for the LIV parameter pairs $(c_{ee},c_{e\mu})$ (left) and $(c_{ee},c_{e\tau})$ (right) assuming normal ordering. The red triangles mark the global minima of each scan, which correspond to the best-fit LIV values preferred by the data. 1$\sigma$ and 3$\sigma$ contours are shown by green and blue lines, respectively.
• Figure 4: Two dimensional $\Delta\chi^{2}$ contours for the LIV parameter pairs $(c_{e\mu}, \phi_{e\mu})$ (left) and $(c_{e\tau}, \phi_{e\tau})$ (right) assuming normal ordering. The red triangles mark the global minima of each scan, which correspond to the best-fit LIV values preferred by the data. 1$\sigma$ and 3$\sigma$ contours are shown by green and blue lines, respectively.
• Figure 5: Sensitivity in the $\sin^2 \theta_{12}- \Delta m_{21}^2$ plane considering best-fit value of CP-violating parameters for $c_{ee}, c_{e\mu}$ (left) and $c_{ee}, c_{e\tau}$ (right). The $3\sigma$ and $1\sigma$ contours of NO and IO are shown by blue and green, respectively. Best fits are pointed by red and violet triangles for NO and IO, respectively.