Resolving Lorentz-Violating New Physics at ESSnuSB Using High-Statistics Complementarity with T2HK

A primary objective for next-generation long-baseline neutrino facilities is the search for Planck-scale Lorentz Invariance Violation (LIV). In this work, we explore the capabilities of the proposed ESSnuSB and T2HK experiments to constrain isotropic, CPT-violating LIV parameters ($a_{\alpha\beta}$). The modifications to oscillation probabilities induced by these LIV parameters can introduce parameter degeneracies with the atmospheric mixing angle $\theta_{23}$ and the Dirac CP-violating phase $\delta_{CP}$, which can potentially result in incorrect determination of the said standard oscillation parameters if we do not account for LIV effects. Through detailed GLoBES simulations, we find that while the second-oscillation-maximum configuration of ESSnuSB yields good constraints on the exact phase of $\delta_{CP}$, its intrinsic neutrino-antineutrino statistical asymmetry persistently leads to wrong octant fake solutions for $\theta_{23}$. By synergizing ESSnuSB's 360 km and 540 km baselines with the complementary, high-statistics measurements from first-maximum configuration of the T2HK's 295 km baseline, we show that the degeneracies are resolved for most LIV parameters. Our analysis reflects how complementarity between ESSnuSB and T2HK provides an effective, matter-independent framework to break LIV-induced degeneracies and establish bounds on Planck-scale LIV physics.