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REVIEW 3 major objections 4 minor 25 references

The paper claims that combining ESSnuSB's 360 km and 540 km baselines with T2HK's high-statistics 295 km first-maximum data resolves LIV-induced θ23-octant and δCP degeneracies for most isotropic CPT-violating parameters a_αβ.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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2026-08-01 05:35 UTC pith:MPS5HS5A

load-bearing objection Competent GLoBES study with a real limitation: the degeneracy-resolution claim is only established for one-LIV-parameter-at-a-time fits, so the headline needs a simultaneous-fit check. the 3 major comments →

arxiv 2607.22163 v1 pith:MPS5HS5A submitted 2026-07-24 hep-ph

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

Himanshu Bora , Debajyoti Dutta , Monjowara Khatun , Abinash Medhi This is my paper
classification hep-ph
keywords Lorentz invariance violationCPT violationneutrino oscillationslong-baseline experimentsESSnuSBT2HKparameter degeneracyθ23 octant
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tries to establish that the combination of two complementary long-baseline neutrino experiments—ESSnuSB, probing the second oscillation maximum, and T2HK, delivering high, balanced statistics at the first maximum—can break the parameter degeneracies that Lorentz-violating new physics introduces into standard neutrino oscillation measurements. Specifically, the joint analysis removes most wrong-octant fake solutions for the atmospheric mixing angle θ23 and keeps the CP phase δCP tightly pinned near its true value, even without relying on large matter effects. If correct, this provides a matter-independent route to constrain Planck-scale Lorentz invariance violation at upcoming facilities, with the notable caveat that degeneracies persist for a few parameters like |a_eτ| and, in one combination, a_ee.

Core claim

Using dedicated simulations of the ESSnuSB 360 km and 540 km baselines and the T2HK 295 km baseline, the authors show that a combined χ² analysis shrinks the allowed (θ23, a_αβ) and (δCP, a_αβ) regions so that the wrong-octant fake solutions produced by isotropic, CPT-violating LIV parameters mostly disappear. The 360 km ESSnuSB baseline alone already rules out the lower octant for a_ττ, |a_eμ|, and |a_μτ|, but leaves two-octant solutions for a_ee and |a_eτ|; T2HK alone also cannot resolve a_ee and |a_eτ|. Synergizing T2HK with either ESSnuSB baseline eliminates these fake octants for most parameters, and the 540 km ESSnuSB + T2HK combination even resolves the a_ee octant that the 360 km com

What carries the argument

The central object is the isotropic, CPT-violating LIV Hamiltonian H_LIV = a_αβ, a Hermitian matrix of energy-independent coefficients that perturb the neutrino and antineutrino effective Hamiltonians with opposite sign and complex conjugation. The degeneracy-breaking mechanism is baseline complementarity: ESSnuSB's long baselines sample the second oscillation maximum, where intrinsic CP asymmetry is large, while T2HK's short, high-intensity baseline samples the first maximum with roughly balanced neutrino and antineutrino statistics. The χ² analysis marginalizes over standard oscillation parameters and, for off-diagonal LIV parameters, the new phase φ_αβ, scanning each a_αβ against θ23 and

Load-bearing premise

The demonstration that degeneracies are resolved for most LIV parameters assumes each a_αβ coefficient is switched on one at a time; the text never states that all six coefficients are freed simultaneously in the fit, and if several are non-zero together the allowed regions could expand and the degeneracies could reappear (Section 3 marginalization description and Section 4.2 fitting procedure).

What would settle it

Re-run the joint ESSnuSB (360 km and 540 km) + T2HK simulation with all six a_αβ coefficients and their phases left free in the test hypothesis, generating true data with, say, a_ee = 2.4×10⁻²³ GeV and |a_eτ| = 1.2×10⁻²³ GeV simultaneously; if the 95% allowed regions in the (θ23, a_αβ) and (δCP, a_αβ) planes then contain lower-octant solutions or δCP ≈ +90°, the central 'resolved for most parameters' claim fails for the simultaneous-LIV case.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

If this is right

  • A joint ESSnuSB + T2HK analysis removes wrong-octant θ23 fake solutions for most a_αβ parameters, with the 540 km + T2HK combination also breaking the a_ee octant degeneracy.
  • The combined setup keeps δCP confined to a tight interval around −90° for all parameters, eliminating the δCP = +90° solution that T2HK alone admits for |a_eτ|.
  • Resolving LIV-induced degeneracies does not require the strong matter effects of a long-baseline experiment like DUNE; precision at the first maximum plus second-maximum CP sensitivity suffices for most parameters.
  • Residual degeneracies persist for |a_eτ| (small lower-octant island in both combinations) and for a_ee in the 360 km + T2HK combination, so those parameters are only partially resolved.
  • The 360 km ESSnuSB baseline individually constrains LIV parameters more tightly than the 540 km baseline due to higher statistics, but adding T2HK brings the 540 km configuration to comparable combined performance.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Because the fits appear to vary one LIV coefficient at a time, the claim that degeneracies are resolved 'for most LIV parameters' may not hold if several a_αβ coefficients are simultaneously non-zero; a multi-parameter fit could expand the allowed regions and reopen some octant degeneracies.
  • The persistent |a_eτ| island suggests that fully covering this parameter may require a third probe with a different energy-matter profile, such as atmospheric neutrinos or an additional baseline, rather than just combining these two beams.
  • Comparing with the authors' earlier ESSnuSB + DUNE study implies a trade-off: matter-enhanced configurations give stronger overall LIV magnitude constraints, while the matter-independent ESSnuSB + T2HK combination trades some constraining power for robustness against matter-model uncertainties.
  • A natural testable extension would be to generate fake data with non-zero a_ee and |a_eτ| together and run the global fit with all six LIV parameters free, checking whether the combined allowed regions expand beyond the single-parameter contours shown here.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 4 minor

Summary. The paper presents GLoBES-based sensitivity projections for the ESSnuSB (360 km and 540 km baselines) and T2HK (295 km) experiments to isotropic, CPT-violating LIV coefficients a_αβ in the SME. The authors study correlations between each a_αβ and θ23 or δCP, and show that while the individual ESSnuSB baselines (especially 540 km) suffer from wrong-octant degeneracies due to neutrino-antineutrino event asymmetry, combining either ESSnuSB baseline with T2HK removes most of these degeneracies. The central claim is that the ESSnuSB+T2HK synergy provides a matter-independent way to break LIV-induced degeneracies and constrain Planck-scale LIV, although residual lower-octant islands remain for |a_eτ| and for a_ee in the 360 km combination.

Significance. If the central claim is correct, the paper provides a useful quantitative projection: it shows that high-statistics first-oscillation-maximum data can substitute for strong matter effects in resolving LIV-induced degeneracies, and it maps which parameters remain difficult. The authors use the standard GLoBES machinery, state benchmark LIV magnitudes explicitly, and provide two-dimensional contours and tabulated allowed ranges. These are concrete, testable predictions. However, the significance is tempered by the fact that the fits vary one LIV parameter at a time, so the resolved-degeneracy claim has not been demonstrated for the generic multi-LIV scenario expected from Planck-scale physics.

major comments (3)
  1. [§4.2 and §3] The marginalization description never states whether the other five a_αβ coefficients are fixed to zero or floated in the fits. The text says only that δ_CP (Fig. 4) or θ23 (Fig. 5) is marginalized, and that for off-diagonal parameters the corresponding φ_αβ is marginalized; this strongly implies each panel has only one LIV magnitude active. If so, the central claim that the combination 'resolves the degeneracies for most LIV parameters' holds only for one-parameter-at-a-time LIV. Since generic Planck-scale LIV would have several non-zero a_αβ, the extra degrees of freedom can reopen the wrong-octant solutions. The authors should state this limitation explicitly or, preferably, perform a simultaneous multi-LIV fit or a representative two-parameter scan to show the degeneracy resolution is robust.
  2. [Fig. 2 caption and Table 2] The Fig. 2 caption reads "a_eτ = 0.7×10^-23 GeV", whereas Table 2 and the text state the benchmark magnitude is |a_eτ| = 1.2×10^-23 GeV. This is an inconsistency in the displayed LIV magnitude for the bi-event plots. Please verify which value was actually used in the simulation and correct the caption or the benchmark table; if the bi-event plots used 0.7, they do not correspond to the same benchmark as the χ² analysis.
  3. [§1/§5, central claim] The abstract claims degeneracies are 'resolved for most LIV parameters,' but Table 3 shows that for a_ee the 360 km + T2HK combination still leaves a lower-octant interval [42.6,43.4]°, and for |a_eτ| both combinations leave a lower-octant island. The paper acknowledges these residuals, so this is not a contradiction, but the phrasing 'resolved for most' could be sharpened to state exactly which parameters remain degenerate; the current wording risks overstating the outcome for a_ee and |a_eτ|.
minor comments (4)
  1. [§1] Typo: 'HHowever' in the fourth paragraph of the Introduction.
  2. [Figs. 4 and 5] Axis labels like 'a /10 23[GeV]' and 'a /10 23[GeV]' are missing subscripts (a_ee, a_μμ, |a_eτ|, etc.) due to formatting; please fix for readability.
  3. [§3] The text says 'these LIV coefficients are marginalized over relevant ranges during the test hypothesis fitting' but does not specify whether the ranges are the same as the plotted ranges in Figs. 4–5. Clarifying this would help reproduction.
  4. [Reproducibility] No GLoBES input files or a link to such files are provided. Given that the paper's main quantitative claims rest on these simulations, releasing the simulation files would significantly increase reproducibility and trust in the results.

Circularity Check

0 steps flagged

No circular derivation: the LIV sensitivity projections are independent GLoBES calculations anchored to external inputs; self-citations to [47] set the framework and illustrative benchmark magnitudes but do not fix the results.

full rationale

The derivation chain is not circular. The core calculation is: take the SME Hamiltonian (2.4)-(2.9), feed NuFIT-6.0 and JUNO parameter values plus the stated ESSnuSB/T2HK configurations into GLoBES, generate data under the null hypothesis a_alpha_beta = 0, and minimize Delta chi^2 (3.1) over test parameters. The resulting contours in Figs. 4-5 and Tables 3-4 are sensitivity projections, not fitted values recycled as predictions; the true LIV coefficients are set to zero, so the 'constraints' are not re-fit inputs. The only self-citations to [47] set the SME framework and provide illustrative benchmark magnitudes ('We adopt the same framework as described in our previous study [47]'; 'Benchmark LIV parameter magnitudes of O(10^-23) GeV are used for illustration, motivated by our previous work [47]'), but these are not the targets of the statistical test and are not used as fitted inputs. No uniqueness theorem or ansatz is imported via [47]; the isotropic CPT-odd restriction is a standard phenomenological choice cited to Kostelecky/Mewes. The acknowledged residual degeneracies for |a_e_tau| and a_ee are honest limitations, and the single-LIV-parameter-at-a-time fits are an internal-validity/coverage caveat, not a circularity: the claim that degeneracies are resolved is not equivalent to the assumption that only one coefficient is nonzero. External anchors (NuFIT, JUNO, GLoBES, experiment design reports) make the result self-contained.

Axiom & Free-Parameter Ledger

1 free parameters · 4 axioms · 0 invented entities

No genuinely new entities are introduced. The analysis uses the established SME operator set, restricts to isotropic CPT-odd coefficients, and borrows detector configurations from design reports. The main hand-chosen inputs are the benchmark LIV magnitudes and the null true-values; the main unstated modelling choice is single-parameter-at-a-time LIV marginalization.

free parameters (1)
  • Benchmark LIV magnitudes (a_ee=2.4, a_μμ=3.0, a_ττ=2.0, |a_eμ|=0.7, |a_eτ|=1.2, |a_μτ|=2.0) ×10^-23 GeV = Illustrative, not fitted
    Selected by hand and 'motivated by our previous work [47]' (Section 3) to draw the bi-event plots; the χ² analysis marginalizes over LIV values, so these are not fitted parameters, but they set the scale of the shown phenomenology.
axioms (4)
  • domain assumption The SME effective Hamiltonian with isotropic CPT-odd coefficients a_αβ (Eqs. 2.4–2.8) correctly describes LIV in neutrino propagation.
    Adopted from Kostelecky–Mewes and prior LIV studies [24,49]; the paper adds no new derivation.
  • domain assumption Only the LIV parameter under study is varied (plus its phase for off-diagonal terms) in the fits; the other LIV coefficients are effectively fixed at zero.
    Section 4.2 describes marginalizing standard parameters and the relevant φ_αβ, but never states simultaneous marginalization over all a_αβ; the 'most LIV parameters' conclusion depends on this.
  • domain assumption The GLoBES detector simulations represent the planned ESSnuSB and T2HK configurations (fluxes, efficiencies, backgrounds, systematics in Table 1).
    No configuration files are shipped; results rest on files 'provided ... on behalf of the ESSnuSB collaboration' and on design-report inputs [20,22,47].
  • ad hoc to paper True data are generated under exact Lorentz symmetry (all a_αβ=0) with θ23=48.5° and δCP=-90°.
    This null-hypothesis design measures sensitivity to fake solutions; it does not probe how well the combination would constrain LIV if the true LIV were nonzero.

pith-pipeline@v1.3.0-alltime-deepseek · 16719 in / 11557 out tokens · 112220 ms · 2026-08-01T05:35:17.673820+00:00 · methodology

0 comments
read the original abstract

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.

discussion (0)

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Reference graph

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