{"id":"7bff8279-d5c2-4c10-bc1c-dd18c54ab4c9","arxiv_id":"2501.12171","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":3.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Combining DUNE and T2HK projections yields tighter constraints on flavor-dependent long-range neutrino interactions than either experiment alone.","lead":"This paper forecasts how the upcoming DUNE and T2HK neutrino experiments could detect long-range forces that treat neutrino flavors differently. It argues that combining both experiments removes ambiguities that each one faces alone, which would produce stronger limits on such new physics.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The isoscalar treatment of the Milky Way as a neutrino source overestimates its neutron content by roughly a factor of four, which likely inflates the projected low-mass L_μ-L_τ sensitivity that underlies the 'most stringent terrestrial limits' claim.","rationale":"The central claim is a quantitative forecast, obtained by converting sensitivity to the potentials V_αβ in Eq. (4) into bounds on the effective couplings G'_αβ in Fig. 1. The potentials are computed under the stated isoscalar assumption for the Milky Way. This assumption is not physically accurate for the neutron content of Galactic baryons, so the L_μ-L_τ potential from the Galaxy is overestimated by about a factor of four. The affected mass range is precisely the low-mass tail below the Galactic-scale distance, which is part of the 'uncharted parameter space' claimed in the paper. If the correction significantly weakens the L_μ-L_τ bound, the statement that DUNE+T2HK yields the most stringent terrestrial limits for all three symmetries would be overstated for that symmetry. I do not elevate the missing simulation details to the primary concern because the companion paper Ref. [1] is the proper venue for those details and the proceedings explicitly refers to it; the source-composition error is a physical assumption that, if wrong, directly changes the headline numbers. The proposed test would settle the issue quantitatively by regenerating the key figure with a realistic composition, and it aligns with the reader's weakest assumption while sharpening it to a specific, testable correction.","tokens_in":5609,"tokens_out":15161,"duration_ms":169195,"concrete_test":"Recompute the Milky Way contribution to V_αβ in Eq. (4) using realistic electron and neutron abundances per baryon (e.g., from a standard solar-abundance mixture) instead of the isoscalar assumption, while keeping the same Galactic mass distribution, and regenerate Fig. 1 for m' ∈ [10^{-35}, 10^{-27}] eV. If the L_μ-L_τ upper limit on G' shifts by more than about 50% relative to the published curve, the isoscalar assumption is a load-bearing systematic; if the shift is smaller, the concern is minor.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The projected constraints rely on the potentials from Eq. (4), with the Milky Way treated as isoscalar (equal electron and neutron densities), as stated in Section II before Eq. (5). For L_μ-L_τ, the potential is sourced by neutrons (Eq. (2)). Galactic baryonic matter is not isoscalar: a standard composition of roughly 74% hydrogen, 24% helium, and 2% metals by mass gives n_e ≈ 0.87 and n_n ≈ 0.13 per baryon, rather than the assumed 0.50 each. The Galactic neutron density is therefore overestimated by a factor of about four, and the computed V_μτ from the Milky Way is correspondingly too large. This matters for mediator masses m' ≲ 10^{-27} eV, where the interaction range reaches the Galactic scale and the Milky Way dominates the total potential; the L_μ-L_τ bounds in Fig. 1 in this regime are then too strong by up to a factor of about two in G'. Since the abstract claims the strongest terrestrial limits over the entire range below 10^{-18} eV, the low-mass portion of that claim is not secured by the stated assumption.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This proceedings paper (NuFact 2024-29) forecasts the sensitivity of DUNE, T2HK, and their combination to flavor-dependent long-range neutrino interactions mediated by ultra-light Z' bosons associated with the anomaly-free symmetries L_e - L_μ, L_e - L_τ, and L_μ - L_τ. The new interaction potentials are sourced by electrons and neutrons in the Earth, Moon, Sun, Milky Way, and cosmological matter. Using simulated data with fixed true values of δ_CP = 223°, sin^2 θ_23 = 0.455, and normal mass ordering, the paper presents 2σ projected upper bounds on the effective coupling G'_αβ versus mediator mass (Fig. 1) and allowed regions in the (V_αβ, δ_CP) and (V_αβ, sin^2 θ_23) planes for DUNE alone, T2HK alone, and their combination (Figs. 2 and 3). The central claim is that each experiment individually suffers from parameter degeneracies, but the combination lifts these degeneracies and yields stronger constraints.","tokens_in":5848,"tokens_out":6279,"duration_ms":66833,"significance":"If the projected sensitivities are correct, the paper would quantify an important physics opportunity for the next generation of long-baseline experiments: probing flavor-dependent long-range neutrino interactions for mediator masses below about 10^-18 eV, a region that is largely unconstrained by terrestrial experiments. A clear strength is that the analysis builds on a mature simulation framework (Ref. [1]) and explicitly shows individual and combined contours, making the claimed complementarity visually evident. A further strength is the paper's recognition that different sources dominate in different mediator-mass ranges, which is essential for understanding the step-like structure of the exclusion curves. However, the quantitative bounds depend on source-composition assumptions that need to be scrutinized, and the proceedings text does not provide enough detail to reproduce the numerical results independently.","major_comments":[{"comment":"The statement that potential sources are treated as isoscalar, with equal electron and neutron counts, is not a good approximation for the Milky Way. For a standard Galactic baryonic composition of about 74% hydrogen, 24% helium, and 2% metals by mass, the neutron fraction per baryon is about 0.13 rather than 0.5. Since V_μτ is proportional to the neutron number N_n (Eq. (2)), the Milky Way contribution to V_μτ is overestimated by roughly a factor of four. For mediator masses m'_μτ ≲ 10^-27 eV, where the interaction range reaches the Galactic scale and the Milky Way dominates the sum in Eq. (4), the projected G'_μτ bounds in Fig. 1 are therefore too strong by up to about a factor of two in G'. This undermines the low-mass portion of the paper's claim to probe largely uncharted parameter space with exceptional sensitivity, and it should be corrected by using a realistic Galactic composition or by explicitly presenting the bounds as order-of-magnitude only. Note that for the electron-sourced L_e-L_μ and L_e-L_τ potentials the same assumption underestimates the electron density, so the direction of the effect is symmetry-dependent.","section":"Section II (text before Eq. (5)); Eqs. (2), (4); Fig. 1"},{"comment":"The paper reports 2σ upper bounds on V_αβ and translates them into constraints on G'_αβ, but it does not describe the simulation, event selection, systematic uncertainties, or test statistic used to derive these bounds. The reader is referred to Ref. [1] for details. Because the central claim of the paper, that the DUNE+T2HK combination provides stronger constraints than either experiment alone, is based on these numerical results, the proceedings should include at least a summary of the statistical procedure and the source contributions used in Fig. 1, or state explicitly that all quantitative results are identical to those of Ref. [1]. As it stands, the standalone content is not checkable from the text.","section":"Section III (Fig. 1)"}],"minor_comments":[{"comment":"The equations contain typographical problems: \"G′2\" is ambiguous and likely should be the square of the relevant coupling, and Eq. (2) contains an unexplained factor \"e / sin θ_W cos θ_W\". Please harmonize the notation with Ref. [1] and define all symbols.","section":"Eqs. (1) and (2)"},{"comment":"The horizontal axis labels contain \"Le − Lau\" in two panels; this should read \"Le − Lτ\".","section":"Figs. 2 and 3"},{"comment":"The sentence \"For antineutrinos, it flips sign, i.e., Vαβ → −Vαβ\" should clarify whether this flip applies only to the new long-range potential or also to the SM matter potential, since the sign convention for the SM matter potential is different in many texts.","section":"Section II, after Eq. (6)"},{"comment":"The text says the Sun and cosmological matter are not treated as isoscalar, but it does not specify the composition assumed for these sources. This information is needed to reproduce the low-mass behavior of Fig. 1.","section":"Section II"},{"comment":"The vertical grid lines in Fig. 1 (labeled \"Causal horizon\", \"1 A.U.\", \"Distance to GC\", \"R⊕\") would be easier to interpret if the corresponding mediator masses were listed in the caption or on the axis.","section":"Section III"}],"recommendation":"major_revision","confidential_remarks":"This is a conference proceedings that closely follows the authors' prior work (Refs. [1] and [13]). The isoscalar composition issue for the Milky Way is the main technical obstacle; it should be straightforward to recompute the Milky Way contribution with standard abundances, and the resulting shift in the low-mass L_μ-L_τ bounds is sizable enough to affect the claimed headline sensitivity. If the authors fix that point and add a brief statistical description, the proceedings would be acceptable. The novelty relative to Ref. [1] is limited, but that is normal for a NuFact contribution."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick read: this is a conference proceedings that condenses the authors' JHEP 2023 paper, not a new analysis. Two of the three figures are explicitly taken from that paper, and the third is a translated version of the same framework. The synergy claim—that DUNE and T2HK together break degeneracies that weaken each experiment individually—is reasonable and consistent with the contours shown. The paper is honest about its provenance, pointing to Ref [1] for all simulation details.\n\nThe main problem is the isoscalar assumption stated before Eq. (4). The authors treat the Milky Way as having equal electron and neutron densities, but galactic baryonic matter is about 74% hydrogen and 24% helium by mass, giving roughly 0.14 neutrons per baryon rather than 0.5. For L_mu-L_tau, where the potential is neutron-sourced, this overestimates the galactic neutron density by a factor of about 3.6. For mediator masses below about 10^-27 eV, where the interaction range reaches the Milky Way, the projected G'_mu_tau limits are therefore too strong by up to a factor of about two. Since the abstract claims the strongest terrestrial limits for the whole range below 10^-18 eV, that low-mass portion is not secured. The same mistake biases the electron-sourced bounds by about 30% in G', so it is not just an L_mu-L_tau issue.\n\nThe other soft spot is the lack of self-containedness. The simulation, systematic uncertainties, and data generation are all in Ref [1]; the proceedings gives no code or data. That is normal for a summary, but it means the forecast cannot be independently checked from this manuscript.\n\nWhat the paper does well: it lays out the three lepton-number symmetries cleanly, the degeneracy plots (Figs 2 and 3) are informative, and the text is candid about what is recycled. The authors are not hiding the ball; this is a pointer to their longer work.\n\nRecommendation: I would desk reject this as a research paper because it offers no new result and carries a physics error in its central assumption. But it is fine as a proceedings placeholder if the authors correct the isoscalar treatment or add a caveat that the low-mass L_mu-L_tau bounds are subject to the Milky Way composition. If you do send it out, the referee will focus on that assumption, and the authors will need to redo the affected part of Fig. 1. My suggestion: talk to the authors, point out the composition issue, and accept a corrected version for the proceedings.","headline":"Useful proceedings summary of a solid JHEP analysis, but not a new result and the isoscalar Milky Way assumption inflates the low-mass L_mu-L_tau limits by about a factor of two.","tokens_in":6368,"tokens_out":5209,"would_cite":false,"duration_ms":52466,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":false},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper forecasts that combining the DUNE and T2HK experiments breaks parameter degeneracies and produces the strongest terrestrial limits on flavor-dependent long-range neutrino interactions from lepton-number symmetries.","keywords":["long-range neutrino interactions","DUNE","T2HK","neutrino oscillations","lepton-number gauge symmetries","ultralight mediators","parameter degeneracies","beyond Standard Model"],"falsifier":"Re-run the combined fit replacing the isoscalar-source treatment with realistic neutron-to-electron ratios for the Earth, Moon, Sun, and Milky Way; if the $2\\sigma$ contour in ($V_{\\alpha\\beta}$, $\\delta_{\\rm CP}$) no longer shrinks relative to the DUNE-only and T2HK-only contours, the synergy claim rests on the simplified source model.","tokens_in":5425,"feed_emoji":"🔭","tokens_out":12958,"duration_ms":116921,"temperature":0.7,"pith_summary":"This paper argues that next-generation long-baseline neutrino experiments can reveal a new class of feeble, long-range forces carried by ultra-light bosons, provided the two flagship experiments are analysed together. These forces would arise from gauging lepton-number symmetries that distinguish electron, muon, and tau neutrinos, and would be sourced by ordinary matter throughout the Earth, the Moon, the Sun, the Milky Way, and the local Universe. The central forecast is that neither DUNE nor T2HK alone can fully tame the degeneracies between the new force strength and the standard oscillation parameters $\\delta_{\\rm CP}$ and $\\theta_{23}$, but the pair together can, yielding the strongest terrestrial upper limits on the effective couplings for mediator masses down to about $10^{-18}$ eV. A reader should care because this is a concrete, testable route to new physics that the upcoming experiments are already positioned to take.","feed_headline":"Pairing DUNE with T2HK sharpens limits on long-range neutrino forces","feed_subtitle":"Joint analysis lifts degeneracies that blunt each experiment alone, probing ultralight mediators below 10^-18 eV.","key_machinery":"The carrying object is the long-range potential $V_{\\alpha\\beta}=G'^2_{\\alpha\\beta}\\,N/(4\\pi d)\\,e^{-m'd}$, sourced by the electron density (for $L_e-L_\\mu$ and $L_e-L_\\tau$) or neutron density (for $L_\\mu-L_\\tau$) of every matter concentration from the Earth to the cosmological background, summed in Eq. (4). This potential is inserted into the propagation Hamiltonian as $H=H_{\\rm vac}+V_{\\rm mat}+V_{\\alpha\\beta}$, with $V_{\\alpha\\beta}={\\rm diag}(V,-V,0)$ for $L_e-L_\\mu$, $V_{\\alpha\\beta}={\\rm diag}(V,0,-V)$ for $L_e-L_\\tau$, and $V_{\\alpha\\beta}={\\rm diag}(0,V,-V)$ for $L_\\mu-L_\\tau$. The second half of the argument is the combined DUNE+T2HK statistical fit, which marginalizes over $\\delta_{\\rm CP}$, $\\sin^2\\theta_{23}$, $\\Delta m^2_{31}$, and the mass ordering and thereby exposes how the two experiments' complementary systematics close the degeneracies.","core_discovery":"DUNE and T2HK, run jointly, break the degeneracies that each experiment faces separately between a long-range flavor-dependent neutrino-matter potential $V_{\\alpha\\beta}$ and the unknown CP phase $\\delta_{\\rm CP}$ and the atmospheric mixing angle $\\theta_{23}$. With this combination the paper derives $2\\sigma$ upper bounds on the potential of $V_{e\\mu}=1.4\\times10^{-14}$ eV, $V_{e\\tau}=1\\times10^{-14}$ eV, and $V_{\\mu\\tau}=0.73\\times10^{-14}$ eV for the three gauged lepton-number symmetries $L_e-L_\\mu$, $L_e-L_\\tau$, and $L_\\mu-L_\\tau$. These translate into projected upper bounds on the effective couplings $G'_{\\alpha\\beta}$ versus mediator mass; below $m'\\sim10^{-18}$ eV the limits enter parameter space that past terrestrial experiments have not probed. The constraints are strongest for $L_e-L_\\tau$, because it affects appearance channels, and weakest for $L_\\mu-L_\\tau$, which enters only through disappearance and through a coupling combination. The physical mechanism is complementarity: DUNE's broad energy range and large matter effect pin down the long-range potential, while T2HK's precision on $\\delta_{\\rm CP}$ and $\\sin^2\\theta_{23}$ removes the nuisance directions that would otherwise hide it.","pith_inferences":["Editorial inference: the same degeneracy-lifting mechanism should apply to other new-physics matter potentials, such as non-standard neutrino interactions, so joint fits are likely to sharpen those limits as well.","Editorial inference: because the forecasts assume isoscalar sources, replacing that assumption with geophysical and astronomical density profiles is a natural next step; the limits could move in either direction, so the source model is the main lever on the projected constraints.","Editorial inference: the step-like transitions in the limit curves as the interaction range crosses Earth-to-Moon, Moon-to-Sun, and Sun-to-Milky Way distances mean that measuring the shape of the curve, not just its endpoints, could identify which matter source dominates the potential and test the model source by source."],"forward_implications":["If the projection holds, an actual DUNE+T2HK data run can set terrestrial limits on all three lepton-number gauge symmetries that are tighter than existing global oscillation, atmospheric, solar, and reactor bounds for mediator masses below about $10^{-18}$ eV.","The combined fit should close the allowed regions in the ($V_{\\alpha\\beta}$, $\\delta_{\\rm CP}$) and ($V_{\\alpha\\beta}$, $\\sin^2\\theta_{23}$) planes that either experiment alone leaves open.","A null result would bound the $L_e-L_\\tau$ interaction most strongly and the $L_\\mu-L_\\tau$ interaction most weakly, matching the paper's ordering $G'_{e\\tau}