Constraining and Resolving Lorentz-Violating New Physics at ESSnuSB Using Complementarity with DUNE

TL;DR

This work examines isotropic CPT-violating Lorentz Invariance Violation within the SME framework using ESSnuSB and DUNE LBL experiments. Through detailed simulations of ESSnuSB's two baselines and DUNE's 1300 km setup, the authors show LIV can mimic standard parameters like $\theta_{23}$ and $\delta_{CP}$, creating degeneracies that shift octant and CP-violation inferences. A joint ESSnuSB+DUNE analysis leverages complementary $L/E$ and matter effects to break these degeneracies and yields strong constraints on LIV coefficients, reaching roughly $\mathcal{O}(10^{-24})$ GeV for off-diagonals and $\mathcal{O}(10^{-23})$ GeV for diagonals. The results underscore the value of multi-baseline, multi-energy strategies to probe Planck-suppressed LIV and demonstrate that combining ESSnuSB with DUNE can substantially tighten LIV limits beyond current bounds.

Abstract

We examine the sensitivity of the ESSnuSB and DUNE long-baseline neutrino experiments to isotropic, CPT-violating Lorentz Invariance Violation (LIV). Using detailed simulations for the 360 km and 540 km ESSnuSB baselines and the 1300 km DUNE setup, we assess how LIV parameters influence oscillation probabilities, event spectra, and degeneracies among oscillation parameters. We find that LIV-induced modifications can closely mimic variations in $θ_{23}$ and $δ_{\rm CP}$, potentially leading to incorrect determination of the atmospheric mixing angle octant and the leptonic CP phase if LIV effects are not accounted for. Although combining the two ESSnuSB baselines improves overall sensitivity, it does not fully remove these degeneracies. In contrast, a joint ESSnuSB+DUNE analysis benefiting from the synergy between second-maximum sensitivity at ESSnuSB and first-maximum, matter-enhanced sensitivity at DUNE can successfully resolve all these degeneracies and can yield significantly stronger constraints on all the LIV parameters. The results presented here highlights the essential role of multi-baseline, multi-energy experimental strategies to probe Planck-suppressed Lorentz-violating new physics.

Figures (14)

• Figure 1: Appearance Probability in presence of LIV parameters, $P_{\mu \rightarrow e}$ and its deviation from Standard Interaction, $\Delta P_{\mu \rightarrow e} = P_{\mu \rightarrow e}({SI+LIV}) - P_{\mu \rightarrow e}(SI)$ as functions of L/E. Effects of individual diagonal LIV parameters ($a_{ee}, a_{\mu\mu}, a_{\tau\tau}$) and effects of off-diagonal LIV parameters ($a_{e\mu}, a_{e\tau}, a_{\mu\tau}$) on $P_{\mu \rightarrow e}$ are shown in the top-left panel and the top-right panel respectively. Bottom-left panel shows $\Delta P_{\mu \rightarrow e}$ in presence of diagonal LIV parameters ($a_{ee}, a_{\mu\mu}, a_{\tau\tau}$) while the bottom-right panel shows that for off-diagonal LIV parameters ($a_{e\mu}, a_{e\tau}, a_{\mu\tau}$), with shaded bands showing the impact of varying the LIV phase $\phi_{\alpha\beta} \in [-\pi, \pi]$. Benchmark LIV parameter magnitude $|a_{\alpha\beta}| = 2 \times 10^{-23}$ GeV for a 1300 km baseline is used for illustration.
• Figure 2: Disappearance Probability in presence of LIV parameters ($P_{\mu \rightarrow \mu}$) and its deviation from Standard Interaction, ($\Delta P_{\mu \rightarrow \mu} = P_{\mu \rightarrow \mu}({SI+LIV}) - P_{\mu \rightarrow \mu}(SI)$) as functions of L/E. Effects of individual diagonal LIV parameters ($a_{ee}, a_{\mu\mu}, a_{\tau\tau}$) and effects of off-diagonal LIV parameters ($a_{e\mu}, a_{e\tau}, a_{\mu\tau}$) on $P_{\mu \rightarrow \mu}$ are shown in the top-left panel and the top-right panel respectively. Bottom-left panel shows $\Delta P_{\mu \rightarrow \mu}$ in presence of diagonal LIV parameters ($a_{ee}, a_{\mu\mu}, a_{\tau\tau}$) while the bottom-right panel shows that for off-diagonal LIV parameters ($a_{e\mu}, a_{e\tau}, a_{\mu\tau}$), with shaded bands showing the impact of varying the LIV phase $\phi_{\alpha\beta} \in [-\pi, \pi]$. Benchmark LIV parameter magnitude $|a_{\alpha\beta}| = 2 \times 10^{-23}$ GeV for a 1300 km baseline is used for illustration.
• Figure 3: Neutrino appearance ($\nu_e$) events in ESSnuSB (top [L=360km] and middle [L=540km] panel) and DUNE (Bottom panel) in presence of diagonal (left panel) and off-diagonal (right panel) LIV parameters.
• Figure 4: Neutrino disappearance ($\nu_e$) events in ESSnuSB (top [L=360km] and middle [L=540km] panel) and DUNE (Bottom panel) in presence of diagonal (left panel) and off-diagonal (right panel) LIV parameters.
• Figure 5: The heatmap of event differences ($\Delta N_{events}$ = $N_{events}(SI+LIV) - N_{events}(SI)$) in $a_{\alpha\beta}-\theta_{23}$ plane for the diagonal LIV parameter $a_{\mu\mu}$ at energies E1, E2, E3 and E4. The grey dashed line mark the critical degeneracy region where the event difference is zero