{"id":"3bfd5d6a-9f47-4a6f-9308-e00a1c125eb7","arxiv_id":"2604.16920","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":4.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":0,"one_line_summary":"New upper limits of 10^{-6} to 10^{-8} on Weak Equivalence Principle violation between neutrinos and photons derived from IceCube events associated with TXS 0506+056 and PKS 0735+178 via Laniakea Shapiro delay.","lead":"This paper uses IceCube-detected high-energy neutrinos from two blazars to test whether neutrinos and photons experience the same gravitational delay from the Laniakea supercluster. The work tightens existing limits on any violation of the Weak Equivalence Principle by one to three orders of magnitude.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"Uncertain neutrino-blazar associations and simultaneity assumption limit reliability of claimed WEP constraints","rationale":"The reader's weakest assumption (simultaneity and correct association) is the load-bearing point for the precision claims. Full text may add details on error propagation, but the concern remains central to whether the headline limits hold.","tokens_in":1678,"tokens_out":323,"duration_ms":26770,"concrete_test":"Extract the exact time lags and Laniakea potential model used; recompute the bound after adding a conservative 1-day emission-time uncertainty for the blazar flare; if the resulting |Δγ| limit weakens by ≥1 order of magnitude the claimed improvement is not supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim derives |Δγ| ≲ 10^{-6}–10^{-8} from the small observed arrival-time difference between IceCube neutrinos and blazar gamma-ray flares, attributing any difference to a violation of WEP via differential Shapiro delay in the Laniakea potential. This requires the neutrino and photons to have been emitted simultaneously and the events to be correctly associated. For TXS 0506+056 the 2017 neutrino has ~3σ association significance in some analyses but is not definitive; similar for PKS 0735+178. Blazar jet emission mechanisms do not guarantee simultaneity between neutrinos and gamma rays. Without quantitative propagation of association probability and emission-time uncertainty into the final bound, the order-of-magnitude improvements cannot be taken at face value.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The paper claims to test Einstein's Weak Equivalence Principle using IceCube neutrino events associated with the blazars TXS 0506+056 and PKS 0735+178. By interpreting the arrival time differences as differential Shapiro delays in the Laniakea supercluster's gravitational potential, it constrains the post-Newtonian parameter difference |Δγ| to approximately 10^{-6}, 10^{-7}, and 10^{-8}, representing improvements of one to three orders of magnitude over previous neutrino-blazar constraints and up to six over SN1987A limits.","tokens_in":1864,"tokens_out":561,"duration_ms":58768,"significance":"Should the associations and simultaneity assumptions prove robust, this work would provide notably tighter bounds on WEP violations between neutrinos and photons, enhancing the role of multi-messenger astrophysics in testing fundamental gravity theories. The specific use of Laniakea potential and these IceCube events adds a new angle to such tests.","major_comments":[{"comment":"The abstract states the final limits on |Δγ| but provides no visible derivation of the time delays, no error budget, and no discussion of association probability or the Laniakea potential model, preventing evaluation of the claimed improvements.","section":"Abstract"},{"comment":"The assumption of simultaneous emission of neutrinos and gamma rays from the blazars is central to the analysis but lacks quantitative support from jet emission models; this creates a circularity where any delay is attributed to WEP violation without accounting for possible intrinsic time offsets.","section":"Methods"},{"comment":"The ~3σ association significance for the TXS 0506+056 IceCube event (and similar for PKS 0735+178) is not propagated as an uncertainty into the final |Δγ| bounds, treating the events as definitively associated despite not being conclusive.","section":"Results"},{"comment":"There is no sensitivity analysis or validation of the Laniakea potential model used for calculating the Shapiro delay, which is load-bearing for the derived constraints.","section":"Discussion"}],"minor_comments":[{"comment":"Clarify the exact meaning of 'violation ... limited to an accuracy of 10^-6' to explicitly state it refers to |Δγ|.","section":"Abstract"},{"comment":"Add specific citations for the 'previous constraints obtained from other high-energy neutrino-blazar associations' mentioned.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper's approach is interesting but the low association significances and unquantified assumptions may limit its immediate impact; suggest the authors provide a detailed error budget in revision."},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for their constructive and detailed review of our manuscript. Their comments highlight important aspects of clarity, assumptions, and robustness that we have addressed point by point below. We have revised the manuscript accordingly where feasible to strengthen the presentation and analysis.","responses":[{"response":"The abstract is designed to be concise and highlight the primary results and improvements. Full derivations of the Shapiro time delays, the error budget, association probabilities, and details of the Laniakea potential model are provided in the Methods and Results sections. To address the referee's concern and improve standalone readability, we will revise the abstract to briefly reference the Laniakea supercluster potential, the simultaneity assumption, and the event associations used.","revision_made":"yes","referee_comment":"[Abstract] The abstract states the final limits on |Δγ| but provides no visible derivation of the time delays, no error budget, and no discussion of association probability or the Laniakea potential model, preventing evaluation of the claimed improvements."},{"response":"This is a substantive point. The simultaneity assumption is standard in multi-messenger WEP tests because current blazar jet emission models lack precise, quantitative predictions for relative neutrino-photon arrival times at TeV-PeV energies. We will expand the Methods section to cite relevant literature on possible intrinsic delays in blazar jets and include a discussion of how such offsets would conservatively affect the derived |Δγ| bounds, thereby reducing the risk of circular attribution.","revision_made":"partial","referee_comment":"[Methods] The assumption of simultaneous emission of neutrinos and gamma rays from the blazars is central to the analysis but lacks quantitative support from jet emission models; this creates a circularity where any delay is attributed to WEP violation without accounting for possible intrinsic time offsets."},{"response":"We agree that the ~3σ associations are not conclusive and that their significance should be reflected in the final constraints. In the revised manuscript, we will propagate the association probabilities as an additional component in the error budget for |Δγ|. The bounds will be presented with this uncertainty included, and we will discuss the conditional nature of the limits given the association significances.","revision_made":"yes","referee_comment":"[Results] The ~3σ association significance for the TXS 0506+056 IceCube event (and similar for PKS 0735+178) is not propagated as an uncertainty into the final |Δγ| bounds, treating the events as definitively associated despite not being conclusive."},{"response":"We acknowledge that the Laniakea potential is central to the analysis. We will add a dedicated subsection in the Discussion providing a sensitivity analysis by varying key parameters of the Laniakea mass distribution within published uncertainties. We will also include references to independent validations of the Laniakea supercluster model to support its application here.","revision_made":"yes","referee_comment":"[Discussion] There is no sensitivity analysis or validation of the Laniakea potential model used for calculating the Shapiro delay, which is load-bearing for the derived constraints."}],"tokens_in":1419,"tokens_out":683,"duration_ms":34349,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The paper applies the Shapiro-delay test in the Laniakea potential to the 2017 IceCube event from TXS 0506+056 and the event linked to PKS 0735+178. It reports new upper limits on |Δγ| of roughly 10^{-6}, 10^{-7}, and 10^{-8} for different cases, which are numerically tighter than earlier neutrino-based bounds and the SN1987A result. That is the concrete addition: fresh numbers from these two pairs using an existing method and potential model. The calculation itself follows the standard post-Newtonian approach already in the literature, so the novelty is limited to the specific events and the updated numerical values. The abstract states the final limits cleanly and notes the claimed improvement factors. That part is straightforward to follow. The soft spots are exactly where the stress-test flagged them. The bounds treat any observed time offset as a possible WEP violation, which requires the neutrino and gamma-ray photons to have been emitted at the same instant and the IceCube events to be correctly associated with the blazars. The TXS 0506+056 association sits at about 3σ in some analyses, not definitive, and blazar jet physics does not guarantee simultaneous neutrino and gamma-ray production. The abstract gives no error budget, no propagation of association probability, and no check on how emission-time uncertainty would loosen the final numbers. Without those steps the order-of-magnitude gains cannot be taken at face value. This work is for specialists tracking incremental multi-messenger gravity tests who want the latest numerical limits from these particular events. A reader looking for robust new evidence on WEP violation will find the assumptions too load-bearing. The paper deserves a serious referee because the calculation is simple to verify and the topic is current, even though the conclusions will need substantial qualification on the timing and association issues.","headline":"The claimed order-of-magnitude WEP improvements rest on unverified simultaneity and association assumptions that the abstract does not resolve.","tokens_in":2347,"tokens_out":447,"would_cite":false,"duration_ms":18990,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"High-energy neutrinos from two blazars constrain violations of the weak equivalence principle for neutrinos versus photons to one part in 100 million.","keywords":["weak equivalence principle","Shapiro delay","IceCube neutrinos","blazars","Laniakea supercluster","post-Newtonian parameter gamma","TXS 0506+056","PKS 0735+178"],"falsifier":"A future observation that firmly associates an IceCube neutrino with one of these blazars but shows a time delay larger than the gravitational delay calculated for Laniakea would require |γ_ν − γ_γ| to exceed the reported limits.","tokens_in":2595,"feed_emoji":"🌌","tokens_out":803,"duration_ms":24971,"temperature":0.7,"pith_summary":"The paper tests whether neutrinos and photons fall the same way in gravity by comparing their travel times from distant blazars. It uses the small arrival-time differences recorded by IceCube and gamma-ray telescopes, together with the known gravitational pull of the Laniakea supercluster, to bound how much the post-Newtonian parameter gamma can differ between the two particles. A sympathetic reader cares because any measured difference would point to physics beyond general relativity, while a null result tightens the requirement that all particles experience the same spacetime curvature.","feed_headline":"Blazar neutrinos tighten equivalence-principle test to 10^{-8}","feed_subtitle":"IceCube events from TXS 0506+056 and PKS 0735+178 improve prior limits by up to three orders of magnitude via Laniakea Shapiro delay.","key_machinery":"Shapiro time delay induced by the gravitational potential of the Laniakea supercluster, used to convert observed arrival-time differences between neutrinos and gamma rays into a bound on the difference in the PPN parameter gamma.","core_discovery":"By associating IceCube neutrino events with the blazars TXS 0506+056 and PKS 0735+178, and attributing the observed time offsets to the Shapiro delay produced by Laniakea’s gravitational potential, the authors obtain upper limits on |γ_ν − γ_γ| of order 10^{-6}, 10^{-7} and 10^{-8} depending on the specific event and the assumed emission time. These bounds improve earlier neutrino-blazar constraints by one to three orders of magnitude and are up to six orders of magnitude tighter than limits derived from SN1987A MeV neutrinos.","pith_inferences":["If the association method is validated on more sources, the technique could be extended to other cosmic messengers such as gravitational waves or ultra-high-energy cosmic rays.","A confirmed violation at the reported precision would immediately motivate targeted searches for Lorentz-violating operators that couple differently to neutrinos.","The Laniakea potential model could be refined with better mass maps, turning the same events into a probe of large-scale structure rather than only a test of gravity."],"forward_implications":["Any theory that predicts different gravitational coupling for neutrinos and photons is now excluded at the 10^{-8} level for high-energy particles.","The same method can be applied to additional IceCube-blazar coincidences to push the limit further without new instrumentation.","The result supplies a new, independent datum that metric theories of gravity must satisfy for particles spanning nine orders of magnitude in energy.","Improved sky localization of future neutrino events will directly translate into tighter bounds on the same parameter."],"fun_headline_variants":["IceCube blazars constrain WEP to 10^{-8}","Blazar neutrinos test equivalence principle to 10^{-8}","TXS 0506+056 sets equivalence limit at 10^{-8} via IceCube","Laniakea Shapiro delay bounds neutrino gamma to 10^{-8}"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"The neutrino and gamma-ray emissions from the blazars are simultaneous and the IceCube events are correctly associated with TXS 0506+056 and PKS 0735+178.","fun_headline_variants_meta":{"raw":{"variants":["IceCube blazars constrain WEP to 10^{-8}","Blazar neutrinos test equivalence principle to 10^{-8}","TXS 0506+056 sets equivalence limit at 10^{-8} via IceCube","Laniakea Shapiro delay bounds neutrino gamma to 10^{-8}"]},"model":"grok-4.3","cost_usd":0.007539,"raw_usage":{"total_tokens":3470,"prompt_tokens":694,"num_sources_used":0,"completion_tokens":78,"cost_in_usd_ticks":75387000,"prompt_tokens_details":{"text_tokens":694,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":2698,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":694,"tokens_out":78,"duration_ms":23829,"temperature":1.0,"reasoning_tokens":2698,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-05-10T06:56:22.312531+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"A future observation that firmly associates an IceCube neutrino with one of these blazars but shows a time delay larger than the gravitational delay calculated for Laniakea would require |γ_ν − γ_γ| to exceed the reported limits.","supporting_citations":[],"review_version":1}