{"id":"34ebf95d-5682-4beb-bfde-4029366a969a","arxiv_id":"2411.09628","paper_version":3,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"A simulation study projects P2SO and combined DUNE/T2HK/P2SO bounds on large extra dimensions, and P2SO's 3-sigma limit on invisible neutrino decay tau3/m3 of 2.11e-11 s/eV.","lead":"Two proposed neutrino experiments, P2SO alone and P2SO combined with DUNE and T2HK, are simulated to see how tightly they could constrain large extra dimensions and invisible neutrino decay. The paper reports projected limits and shows that neutrino decay, unlike extra dimensions, could noticeably distort future measurements of CP violation and the atmospheric octant.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The LED bounds in Sec. 4 depend on an unvalidated two-mode truncation and a perturbative m_D RED expansion; the omitted KK weight is ~24% of the sterile admixture.","rationale":"The reader's primary concern is P2SO simulation fidelity due to unreleased code. That is real, but a more identifiable and checkable correctness risk sits inside the presented method: the LED results use a two-KK-mode truncation plus a perturbation expansion that is only valid for m_D RED << 1. This affects exactly the numbers that the paper advertises as its LED projections. The decay results in Sec. 5 are less affected by this issue because they use a different, closed-form oscillation probability, so the overall verdict remains CONDITIONAL rather than REJECT. I partially agree with the reader: their simulation-fidelity concern is related but broader, whereas the truncation/expansion issue is a concrete, internally verifiable weakness. The proposed test is computational and would settle whether the omitted KK modes and higher-order corrections move the bounds. If the test passes, the concern is benign; if it fails, the LED bounds are not supported as stated. Therefore I would keep the reader's CONDITIONAL verdict unchanged while directing attention to the specific numerical check rather than only to missing code.","tokens_in":19397,"tokens_out":10610,"duration_ms":114288,"concrete_test":"Recompute the LED chi^2 for the Table II benchmark points (m0=0, RED=0.361 um for P2SO; RED=0.320 um for DUNE+T2HK+P2SO) with nKK = 1, 2, 3, 5, 10 using the exact expressions in Eqs. (9)-(11), and compare with the infinite-tower limit obtained by numerical convergence or an analytic resummation. If Delta chi^2 changes by more than about one unit at any benchmark, or if the extracted 90% C.L. RED thresholds shift by more than 10%, the published LED bounds are not robust to the truncation and the central claim should be revised.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing premise is the numerical LED probability engine behind all of Sec. 4. The paper explicitly adopts m_D RED << 1 ('this assumption is adopted throughout the analysis') and truncates the KK tower at two modes. At the headline RED boundaries the expansion parameter is not negligible: for m0 = 0 and RED = 0.361 um, m3^D RED is about 0.09, and for scanned points with larger m0 the product reaches O(0.1-1). More importantly, retaining n = 1,2 carries only sum_{n=1,2} 1/n^2 = 1.25 of the infinite-tower weight sum_{n>=1} 1/n^2 = 1.64; modes n >= 3 contribute about 24% of the total (L0n)^2 normalization. The paper says that including more KK modes has 'minimal effect', but no numerical comparison is shown. Since the 90% C.L. RED bounds in Table II (0.361, 0.320, 0.414 um) are extracted from small differences between spectra with and without LED, a missing quarter of the sterile-KK admixture, or second-order corrections to L0n, can shift chi^2 by O(1) and move the reported bounds. This concern is internal to the paper's calculation and is independent of the separately noted lack of released P2SO configuration files.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper performs sensitivity projections for two BSM scenarios at the proposed P2SO long-baseline experiment, with DUNE and T2HK included for comparison in the LED part. For LED, the authors use a Kaluza-Klein-tower neutrino-mass model with parameters m0 and R_ED, simulate P2SO, DUNE, and T2HK with GLoBES using a modified probability engine, and report 90% C.L. bounds under different marginalization and systematics assumptions. The headline results are that P2SO alone excludes R_ED > 0.361 μm and the DUNE+T2HK+P2SO combination excludes R_ED > 0.320 μm when all oscillation parameters are marginalized and systematics are included (Table II). For invisible decay of nu_3, the paper finds that P2SO can exclude tau3/m3 below 2.11e-11 s/eV at 3 sigma (Table IV). The paper also studies the impact of the two new-physics scenarios on CP-violation, mass-ordering, and octant sensitivities, accounting for the results with analytical expressions in Eqs. (16) and (22)-(23).","tokens_in":19702,"tokens_out":13227,"duration_ms":126165,"significance":"If the numerical engine is reliable, these are useful and previously unavailable P2SO-specific projections for LED and invisible neutrino decay. The analysis includes a full GLoBES simulation with Poisson statistics, pull-based systematics, and marginalization over oscillation parameters, and it compares the P2SO results with existing constraints and with DUNE/T2HK projections. The analytical expressions in Section 4.2 and Section 5.2 provide useful context for the numerical behavior. However, the LED part does not currently validate its two main approximations: the perturbative expansion in m_D^i R_ED and the restriction to two KK modes. Since the headline bounds in Table II are extracted from small spectral distortions, these approximations are load-bearing and need numerical justification before the projections can be relied upon.","major_comments":[{"comment":"The analysis explicitly adopts the expansion m_D^i R_ED << 1 'throughout', but the scanned parameter space in Fig. 3 includes points with m0 R_ED of order unity or larger (for example, m0 = 1 eV and R_ED = 0.5 μm gives m0 R_ED roughly 2.5 in natural units), and even at the headline m0 = 0 row of Table II (R_ED = 0.361 μm) the product m_3^D R_ED is about 0.09. Because the 90% C.L. bounds are obtained from small differences between spectra with and without LED, the perturbative probability engine should be benchmarked against the exact diagonalization of Eq. (7) over the full reported scan region, or the scan should be restricted to the region where the expansion is under control.","section":"Section 4.1, Eqs. (9)-(12), footnote 1"},{"comment":"The statement that including more than two KK modes has 'minimal effect' is not supported by any numerical comparison shown in the paper. In the small-mass limit, the retained n = 1, 2 modes contribute sum_{n=1,2} 1/n^2 = 1.25 of the sterile-KK normalization while the full tower gives pi^2/6 roughly equal to 1.64, so modes n >= 3 represent roughly 24% of the KK admixture. Since the LED correction to the standard spectra is itself small, omitting this fraction can shift chi^2 by O(1) near the Table II boundaries. The authors should provide a direct comparison of the R_ED bounds with 2, 3, 5, and 10 KK modes (or an all-mode treatment) before the quoted limits can be considered robust.","section":"Section 4.1, final paragraph"},{"comment":"The coefficients A, B, and C in Eq. (17) are quoted to three significant figures without derivation and with unspecified dimensions, and they appear to be numerical fits to a particular realization of the oscillation probability. The paper should state how these coefficients were obtained, over which parameter range they are valid, and how they depend on theta_23 and Delta m^2_31; without this information, Eq. (16) cannot serve as an independent cross-check of the numerical engine or as the basis for the qualitative claim that the LED term is always negative.","section":"Section 4.2, Eqs. (16)-(17)"},{"comment":"The P2SO, DUNE, and T2HK simulation configuration files and the modified probability engine are not provided, and the detector response and systematics are taken from Refs. [57, 58, 62, 64] and prior group papers. Since every projected bound in Tables II and IV depends on this implementation, the manuscript should include at least benchmark event-rate tables for the standard no-new-physics spectra (or a repository link) so that the detector response, binning, and systematic pulls can be checked by independent readers.","section":"Section 3"}],"minor_comments":[{"comment":"The phrase 'exclude tau3/m3 below 2.11e-11 s/eV' is ambiguous about the inequality direction; the authors should state explicitly that short lifetimes (small tau3/m3) are excluded, i.e., tau3/m3 > 2.11e-11 s/eV at 3 sigma, and align the table headings with this convention.","section":"Section 5.3.1 and Table IV"},{"comment":"The column header 'Sensitivity |Delta sqrt(Delta chi^2)|' is confusing; it should state that the entries are the absolute change in significance in sigma when R_ED is varied from 0 to 0.5 μm.","section":"Table III"},{"comment":"The matter density profile used for each baseline is not specified even though Eq. (15) is solved with constant matter density; the values used for P2SO, DUNE, and T2HK should be given explicitly.","section":"Sections 2.2-2.3 and Eq. (15)"},{"comment":"The sentence specifying units ('RED, L and E_nu are in eV^-1, eV^-1 and eV respectively') should also specify the units of A, B, and C, which appear to carry eV^2 dimensions; as written the dimensional analysis is not transparent.","section":"Eq. (16)"},{"comment":"The phrase '3 sigma C.L.' is imprecise because a confidence level requires specifying the number of degrees of freedom; please use '3 sigma' or state the corresponding C.L. explicitly.","section":"Throughout"},{"comment":"Several words are run together in the text (for example, 'ThecapabilityoftheP2SOexperiment' and 'dottedorangerepresent'), which should be corrected in production.","section":"Section 5.3.1"}],"recommendation":"major_revision","confidential_remarks":"The paper is in scope for a hep-ph journal and the novelty is modest but acceptable for a P2SO-focused projection study. The main risk is not the physics idea but the validation and reproducibility of the LED numerical engine: the two-mode truncation, the perturbative expansion, and the fitted coefficients in Eq. (17) are not documented to the level needed for the headline bounds. I would encourage asking the authors for benchmark material and a KK-mode convergence check. I see no citation or attribution concerns."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this is a competent GLoBES sensitivity study that gives the first P2SO projections for large extra dimensions and invisible neutrino decay, plus first combined DUNE+T2HK+P2SO LED bounds. If I worked on P2SO or on LED constraints, I would want it on file. But the LED half has a load-bearing approximation that needs more support before I trust the headline RED numbers.\n\nWhat is genuinely new is the P2SO-specific treatment, the systematic scan over marginalization choices and systematics, the combined three-experiment setup, and the side checks of CPV, mass ordering, and octant shifts in the presence of LED. The decay section is cleaner: it uses the standard non-Hermitian Hamiltonian, analytic formulas from the literature, and gives a tau3/m3 < 2.11e-11 s/eV bound that sits coherently between MOMENT/ESSnuSB and DUNE/T2HK. The text is readable and the figures support the narrative.\n\nWhere it gets soft is the LED probability engine. The paper adopts m_D RED << 1 throughout and truncates the KK tower at two modes, with a one-line claim that more modes have 'minimal effect'. At the headline bound RED ~ 0.36 microns, m3^D RED is about 0.09, and for larger m0 the product grows toward O(0.1-1). Keeping only n = 1,2 retains 1.25/1.64 of the (L0n)^2 tower weight, so roughly a quarter of the sterile admixture is dropped. Since the RED bounds are extracted from small chi^2 differences between spectra with and without LED, a 20-25% shift in the LED-induced term can plausibly move the quoted 0.320-0.414 micron numbers. This is not a refutation, but it is an unvalidated approximation sitting under the main numerical result. A numerical scan over KK modes, or a bound on the truncation error, is needed. The coefficients A, B, C in Eq. 16 are presented as numerical fits without derivation; they are useful for illustration but should be labeled as fits. No simulation files are released, which is common in this literature but makes the P2SO configuration hard to audit independently; the reader has to trust earlier group papers.\n\nProportion check: the decay part is fine, and the LED sensitivity-degradation section is robust because the effects are small and the conclusion is mild impact. The core fragility is specifically the Table II exclusion bounds.\n\nRecommendation: send it to peer review. It is a serious phenomenological study with a new target experiment, and the issues are addressable. A referee should ask for a demonstrated KK truncation convergence and a justification or removal of the perturbative expansion in the scanned region.","headline":"Solid, useful P2SO sensitivity study, but the headline LED bounds rest on an unvalidated two-mode KK truncation and a perturbative expansion that is strained at the quoted limits.","tokens_in":20230,"tokens_out":3735,"would_cite":true,"duration_ms":35989,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["14.60.Pq","12.60.-i"],"model":"deepseek-v4-flash","headline":"Combining the proposed P2SO, DUNE, and T2HK long-baseline neutrino experiments would, according to this simulation study, set the extra-dimension radius below 0.320 micrometers and give P2SO a competitive invisible-decay limit.","keywords":["large extra dimensions","invisible neutrino decay","P2SO","DUNE","T2HK","Kaluza-Klein modes","long-baseline neutrino oscillation","CP violation sensitivity"],"falsifier":"Run the same sensitivity analysis with the P2SO experiment's own official simulation configuration; if the resulting 90% C.L. exclusion on RED or the 3-sigma bound on tau3/m3 deviates from the values quoted here, the projections are not robust. A direct experimental check is the shape of the nu_e appearance spectrum, which should show fast oscillation wiggles growing with RED in P2SO's first data.","tokens_in":1714,"feed_emoji":"⚛️","tokens_out":1887,"duration_ms":92501,"temperature":0.7,"pith_summary":"This paper estimates what the proposed P2SO long-baseline neutrino experiment could learn about two beyond-the-standard-model ideas: large extra dimensions and invisible neutrino decay. For extra dimensions, it claims that P2SO alone would exclude an extra-dimension radius above 0.361 micrometers at 90% confidence when all oscillation parameters are marginalized and systematics are included, and that adding P2SO to DUNE and T2HK would strengthen the exclusion to 0.320 micrometers. For neutrino decay, it claims P2SO could exclude decay parameters below 2.11 x $10^{-11}$ s/eV at 3 $\\sigma$, better than ESSnuSB and MOMENT but weaker than DUNE and T2HK. The paper also assesses how each new-physics effect would alter the experiment's ability to measure CP violation, mass ordering, and the octant.","feed_headline":"Neutrino trio caps extra-dimension radius at 0.32 microns","feed_subtitle":"A 2,595-km beam plus DUNE and T2HK would beat current bounds, and P2SO alone would also constrain invisible neutrino decay.","key_machinery":"The analysis uses a modified long-baseline simulation engine implementing two new-physics extensions: for LED, an infinite Kaluza-Klein tower from a 5-D singlet neutrino field compactified on a circle of radius RED, with Dirac mass m0 and the perturbative regime m_D RED << 1; for invisible decay, a non-Hermitian Hamiltonian that depletes the nu3 state with the decay parameter tau3/m3. The LED distortion is carried by the fast-oscillating factor L/(2 E $R_ED^{2}$), while the decay depletion enters through exponential damping factors. Sensitivities are evaluated with a Poisson log-likelihood including pull-based systematic uncertainties and marginalization over the oscillation parameters.","core_discovery":"The central claim is that the 2,595-km P2SO beam and its few-megaton Cherenkov detector can serve as a competitive probe of both large extra dimensions and invisible neutrino decay. For extra dimensions, the signature is a fast-oscillating distortion of the neutrino appearance and disappearance probabilities, so P2SO alone can set a 90% C.L. bound RED < 0.361 micrometers once all oscillation parameters are marginalized and systematics are included; combining with DUNE and T2HK gives RED < 0.320 micrometers, and the ideal case with fixed parameters and no systematics improves the bound to 0.175 micrometers. For invisible decay, P2SO would exclude tau3/m3 below 2.11 x $10^{-11}$ s/eV at 3 $\\sigma$. The paper further claims that LED has only a mild effect on CP-violation, mass-ordering, and octant sensitivities, whereas decay degrades CP-violation sensitivity and produces a non-monotonic octant sensitivity because of a degeneracy between theta23 and the decay parameter.","pith_inferences":["A natural step the paper does not take is to run the invisible-decay analysis for the DUNE+T2HK+P2SO combination; the synergy shown for LED suggests the combined decay bound would improve on any single experiment.","P2SO's long baseline is a plausible reason it beats the shorter-baseline DUNE+T2HK combination on LED, since the LED distortion scales with L/E; this makes baseline choice as important as detector size for such searches.","The non-monotonic octant sensitivity implies that searches for neutrino decay and for the theta23 octant in P2SO data cannot be separated cleanly, and a joint two-dimensional fit would be needed to avoid misattributing one effect to the other.","The quoted bounds assume 200 MeV energy bins; because the LED signature is fast oscillatory wiggles, testing how the bounds vary with bin width and energy resolution would show whether the projections are conservative or optimistic."],"forward_implications":["If the LED scenario is right, DUNE+T2HK+P2SO would already surpass the current combined MINOS/MINOS+, Daya Bay, and KATRIN limit (RED < 0.250 micrometers) even with all oscillation parameters free.","P2SO alone would produce a stronger LED bound than DUNE+T2HK combined, making it a standalone probe of extra dimensions without waiting for the other two experiments.","Marginalizing over delta m^2_31 weakens the LED bound more than any other single parameter, so improving the precision of the atmospheric mass-squared difference is the key lever for future LED searches.","P2SO's 3-sigma exclusion of tau3/m3 below 2.11 x 10^-11 s/eV would place it between MOMENT and ESSnuSB on one side and DUNE and T2HK on the other among projected decay limits.","If decay affects CP violation and octant as described, P2SO data analyses that ignore decay could mis-reconstruct delta_CP and the theta23 octant."],"supporting_citations":[{"why":"Supplies the P2SO technical design used for detector response, beam power, runtime, and systematic uncertainties.","marker":"[57, 58]"},{"why":"Provides the P2SO simulation configuration details adopted in this analysis.","marker":"[59-61]"},{"why":"Provides the long-baseline simulation software whose probability engine is modified for LED and decay.","marker":"[65, 66]"},{"why":"Provides the best-fit oscillation parameters and errors used as truth values in both new-physics analyses.","marker":"[69]"},{"why":"Derives the matter evolution equation for LED that the probability engine implements.","marker":"[71]"},{"why":"Supplies the three-flavor analytic probabilities for invisible neutrino decay in matter used to explain the numerical results.","marker":"[79, 81]"},{"why":"Provides the current combined bound on RED from MINOS/MINOS+, Daya Bay, and KATRIN against which the projected bounds are compared.","marker":"[16]"},{"why":"Provides the MOMENT projected sensitivity to tau3/m3 against which P2SO's decay bound is compared.","marker":"[82]"},{"why":"Provides the ESSnuSB projected sensitivity to tau3/m3 against which P2SO's decay bound is compared.","marker":"[54]"},{"why":"Provides projected T2HK and DUNE sensitivities to tau3/m3 against which P2SO's weaker decay bound is measured.","marker":"[55, 56]"}],"fun_headline_variants":["P2SO trio tightens extra-dimension radius to 0.32 microns","P2SO alone can set bounds on invisible neutrino decay","Extra dimensions and neutrino decay: P2SO probes both","Trio of neutrino experiments shrinks extra-dimension limit","P2SO excludes tau/m < 2.11e-11 s/eV for decay"],"cache_read_input_tokens":22400,"weakest_assumption_plain":"The projected bounds rest on the assumption that the simulation, including its detector response, backgrounds, energy bins, and systematic uncertainties, faithfully represents the P2SO experiment as it would actually run.","fun_headline_variants_meta":{"raw":{"variants":["P2SO trio tightens extra-dimension radius to 0.32 microns","P2SO alone can set bounds on invisible neutrino decay","Extra dimensions and neutrino decay: P2SO probes both","Trio of neutrino experiments shrinks extra-dimension limit","P2SO excludes tau/m < 2.11e-11 s/eV for decay"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001014,"raw_usage":{"total_tokens":4295,"prompt_tokens":971,"completion_tokens":3324,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":587,"completion_tokens_details":{"reasoning_tokens":3230}},"tokens_in":587,"tokens_out":3324,"duration_ms":26975,"temperature":1.0,"reasoning_tokens":3230,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T20:27:00.457628+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run the same sensitivity analysis with the P2SO experiment's own official simulation configuration; if the resulting 90% C.L. exclusion on RED or the 3-sigma bound on tau3/m3 deviates from the values quoted here, the projections are not robust. A direct experimental check is the shape of the nu_e appearance spectrum, which should show fast oscillation wiggles growing with RED in P2SO's first data.","supporting_citations":[{"cited_title":"Barbieri, P","cited_arxiv_id":null,"evidence_quote":"Provides the current combined bound on RED from MINOS/MINOS+, Daya Bay, and KATRIN against which the projected bounds are compared."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the ESSnuSB projected sensitivity to tau3/m3 against which P2SO's decay bound is compared."}],"review_version":1}