Anisotropic Lorentz invariance violation in reactor neutrino experiments

TL;DR

This work tests anisotropic Lorentz invariance violation (LIV) in reactor neutrino oscillations by embedding a direction-dependent LIV term into the SME framework and assessing its impact on the standard 3ν analysis of Double Chooz, RENO, and Daya Bay. Using GLoBES simulations and a pull-based $\chi^2$ approach, the authors explore 12 LIV parameters, finding that the LIV coefficient $\mathcal{A}^{\text{C(0)}}_{31}=2.43\times10^{-17}$ MeV provides the best global fit, with $\sin^22\theta_{13}$ and $\Delta m^2_{ee}$ shifting minimally and the parameter goodness-of-fit rising to $p_{\text{PG}}=0.57$ (versus $0.14$ under SM). The analysis also reveals that RENO and Daya Bay results become more consistent under LIV, while Double Chooz remains largely unaffected due to its orientation relative to the LIV axis. The results motivate future tests at next-generation facilities such as JUNO to further probe anisotropic LIV in neutrino oscillations.

Abstract

Recent reactor neutrino oscillation experiments reported precision measurements of $\sin^2 2θ_{13}$ and $Δm^2_{ee}$ under the standard 3$ν$ oscillation framework. However, inter-experiment consistency checks through the parameter goodness-of-fit test reveal proximity to the tension boundary, with the Double Chooz, RENO, and Daya Bay ensemble yielding $p_\text{PG}=0.14$ vs threshold $α=0.1$. Anisotropic Lorentz invariance violation (LIV) can accommodate this tension by introducing a location-dependent angle $θ^\text{LIV}$ relative to the earth's axis. It is found that anisotropic LIV improve the fit to data up to 1.9$σ$ confidence level significance, with the coefficient $\mathcal{A}^{C(0)}_{31} = 2.43\times 10^{-17}\text{ MeV}$ yielding the best fit, while Parameter Goodness-of-fit (PG) is significantly improved within the LIV formalism.

Figures (4)

• Figure 1: The sketch to show how antineutrinos propagate along the Earth's surface. The silhouette of Earth's northern hemisphere is with the rotation axis as the Z-axis. The red dot represents the geographical location of the detector, while the label "S" marks the due south at this point.
• Figure 2: Shifts of neutrino oscillation parameters under LIV effects. The red and blue correspond to the 90% C.L. analysis results of standard neutrino oscillation and LIV oscillation respectively, assuming normal mass hierarchy.
• Figure 3: $\chi^2$ curves for $\sin^2 2\theta_{13}$ analysis of each experiment after introducing the LIV parameter $\mathcal{A}^{C(0)}_{31}=2.43\times10^{-17}\text{ MeV}$. The red, green, and blue colors correspond to the Double Chooz, RENO, and Daya Bay experiments, respectively. The solid lines represent the $\chi^2$ curves under the effect of LIV, while the dashed lines are in the standard neutrino oscillation case. $\Delta m^2_{ee}$ is fixed at $2.519\times10^{-3}\text{ eV}^2$, assuming normal mass hierarchy.
• Figure 4: 90% C.L. space of neutrino oscillation parameters for the RENO and Daya Bay experiments after introducing $\mathcal{A}^{C(0)}_{31}=2.43\times10^{-17}\text{ MeV}$. The red and blue colors represent the results of Daya Bay and RENO, respectively. The star markers indicate the best-fit points, assuming normal neutrino mass hierarchy. Double Chooz is excluded owing to its absence of a precise $\Delta m^2_{ee}$ measurement DoubleChooz:2019qbj.