{"id":"a3dfa1a4-fe6d-46b6-ab34-0d44edd69962","arxiv_id":"2506.23113","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":2.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"In the minimal flipped SU(5) model with radiative seesaw, successful thermal leptogenesis implies an upper limit on the lightest neutrino mass of about 3 x 10^-2 eV, testable at KATRIN.","lead":"An analysis of a highly constrained grand unified theory variant finds that matching the observed matter-antimatter asymmetry through leptogenesis requires the lightest neutrino to weigh less than about 0.03 eV. This makes the model testable in current beta-decay experiments such as KATRIN and tightens predictions for proton decay channels.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The thermal-leptogenesis-only assumption is unquantified: U(1)_X breaking at the unification scale can generate B-L, and the paper neither computes it nor demonstrates washout, so the m1 bound is not yet a robust model prediction.","rationale":"The reader identified the same load-bearing concern: the analysis assumes thermal leptogenesis is the primary source of net B-L without quantifying the high-scale B-L that can be generated when the (10,+1) scalar breaks U(1)_X. This is the correct weakest point because the central claim, the m1 < 3e-2 eV upper limit, is literally a comparison between a thermal-only eta_B calculation and the observed asymmetry. If a pre-existing B-L contribution is non-negligible, the required thermal contribution is smaller, and the stated bound does not follow. The paper does flag this assumption explicitly, so this is not an internal inconsistency; it is an unvalidated physical premise. The concern is strengthened by the internal tension with Domain A: the suppressed washout that makes N1-dominated leptogenesis work also protects any earlier B-L asymmetry from erasure. A second, more presentation-level issue is that Fig. 2 is for normally ordered neutrinos only, while the text states the bound without that qualifier; however, that is an overclaim in scope rather than the deeper physical premise. The proposed concrete test, computing the U(1)_X-breaking B-L yield and injecting it into the Boltzmann solver, would settle whether the assumption actually holds in the relevant parameter region. Since the authors themselves present the thermal-leptogenesis condition as hypothetical, the current CONDITIONAL verdict remains appropriate; no change is needed, but the stated prediction should be understood as conditional on the unquantified high-scale B-L being negligible.","tokens_in":5939,"tokens_out":6051,"duration_ms":69636,"concrete_test":"Compute the B-L yield from CP-violating decays of the (10,+1) scalar and the U(1)_X gauge bosons at the unification scale, using the same Yukawa couplings and mass spectrum as Ref. [12]; for each scan point with m1 > 3e-2 eV, add this yield as an initial condition to the ULYSSES Boltzmann equations and track its washout through the RHN era. If any such point gives a total eta_B >= 6e-10, the m1 bound is an artifact of the sole-source assumption.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central numerical result is the upper limit m1 < 3e-2 eV, obtained by comparing ULYSSES thermal-leptogenesis yields to the observed eta_B ~ 6e-10. This comparison is valid only if all other B-L sources are negligible. Section 2.1 explicitly acknowledges that in the genuine flipped SU(5) the (10,+1) scalar breaks U(1)_X at the unification scale and 'a net B-L may be first produced well above the seesaw scale', but then simply assumes thermal leptogenesis is primary. That assumption is not derived: CP-violating decays of the heavy fields that break U(1)_X can generate B-L at M_GUT, and because the seesaw scale is radiatively generated around 1e8 GeV, there is a large separation over which such an asymmetry can be produced before RHN interactions turn on. Moreover, the paper's Domain A, the parameter region where the desired eta_B is attained, requires relatively suppressed washout for N1; the same weak washout would also preserve any pre-existing high-scale B-L. Thus the escape clause 'strong washout precedes' is in tension with the very domains that give the quoted bound. If a pre-existing B-L yield is even comparable to the thermal yield, the required thermal yield is smaller, and m1 > 3e-2 eV may become viable; the KATRIN testability claim then rests on an unvalidated premise rather than on the model's structure.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript studies baryogenesis via thermal leptogenesis in the minimal flipped SU(5) model where the right-handed neutrino Majorana mass scale is generated radiatively at two loops. It claims that imposing the observed baryon asymmetry eta_B ~ 6e-10 as a requirement selects parameter regions in which the lightest active neutrino mass m1 is bounded above by about 3e-2 eV, that this bound translates into a prediction for the effective neutrino mass m_beta testable by KATRIN, and that the compatible parameter region also implies BR(p -> pi0 mu+) < 30%. The paper explicitly assumes that thermal leptogenesis is the primary source of net B-L, acknowledging that high-scale B-L generation may occur at U(1)_X breaking. The numerical results are taken from a previous paper [12] that used the ULYSSES package, and Fig. 2 shows a sample scan cut.","tokens_in":6197,"tokens_out":2862,"duration_ms":32527,"significance":"If the central claim is correct, the paper offers a concrete connection between cosmological baryogenesis and low-energy neutrino observables, with a falsifiable upper bound on the absolute neutrino mass scale and a characteristic proton decay branching ratio pattern. The strength of the paper is its explicit model context and the use of a dedicated leptogenesis solver (ULYSSES) in the companion work [12]; the manuscript also honestly states its central assumption. However, the upper limit is not a theorem of the model alone; it depends on an unquantified assumption about the absence of competing high-scale B-L sources and on numerical details that are not reported here. The significance is therefore conditional: it would be high if the assumption can be justified or quantified, but as it stands the robustness of the claimed bound is not established.","major_comments":[{"comment":"The manuscript assumes that thermal leptogenesis is the primary source of net B-L, but it explicitly acknowledges that in the genuine flipped SU(5) the (10,+1) scalar breaks U(1)_X at the unification scale and that 'a net B-L may be first produced well above the seesaw scale'. This is a load-bearing assumption for the central m1 < 3e-2 eV bound: if any comparable B-L is generated at M_GUT through CP-violating decays of the heavy fields, the required thermal yield is reduced and the upper limit on m1 does not follow. The paper does not estimate the high-scale asymmetry or demonstrate that it is washed out. Moreover, the parameter region that yields the quoted bound (Domain A in Sec. 2.2) is characterized by 'relatively suppressed washout', which would also preserve a pre-existing asymmetry. The escape clause 'strong washout precedes' is thus in tension with the very domain used to obtain the bound. Please either quantify the high-scale B-L yield and washout or state explicitly that the bound holds only under an additional, unverified assumption.","section":"Sec. 2.2, Fig. 2"},{"comment":"The numerical results supporting the upper limit m1 < 3e-2 eV are not described in sufficient detail. The paper refers to a 'sample scan' and to Ref. [12] for the ULYSSES computation, but the present manuscript presents no information on scan ranges, number of points, convergence criteria, or sensitivity to input quantities such as quark masses, phases, and renormalization-group uncertainties. Since the upper limit is the main new physical statement of this paper (as opposed to Ref. [12], which may have different scope), the reader cannot assess whether the limit is robust or an artifact of a particular parameter cut. Please provide these details or explicitly defer the full analysis to Ref. [12] and describe which parts of the result are new here.","section":"Sec. 2.2, Fig. 2"},{"comment":"The claimed universal bound BR(p -> pi0 mu+) < 30% in the eta_B-compatible region is stated without showing the scan that leads to it. The proton decay branching ratio depends on the U_nu matrix (Eq. (2)), which in turn depends on the same high-scale parameters and on the assumption about thermal leptogenesis dominance. It is not clear from the text whether this bound is a hard constraint across all of the eta_B-compatible parameter space or a feature of the sampled points. Please clarify the provenance of this bound and its dependence on the assumptions in Sec. 2.1.","section":"Sec. 2.3"}],"minor_comments":[{"comment":"There are several typographical errors, e.g., 'neturino' in Sec. 2.2 and 'theoris' in the Introduction; the manuscript would benefit from a careful proofreading pass.","section":"Abstract / Sec. 2.2"},{"comment":"The caption of Fig. 2 mentions a log-log plane but does not label the axes in the figure; please add axis labels and units so the reader can understand the 'triangular shape' without referring to Ref. [12].","section":"Fig. 2"},{"comment":"The phrase 'the current scenario' is used multiple times with differing referents; please clarify whether it denotes the minimal flipped SU(5) model with radiative seesaw, the thermal-leptogenesis scenario, or the specific parameter scan of Fig. 2.","section":"Sec. 2.1"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"This is a conference proceedings that repackages the authors' own PRD 110, 015030 numerical scan. Nothing numerically new is computed here; the paper explicitly says the result 'is exactly what has been observed in a dedicated analysis of Ref. [12]'. What is new is the packaging: the claim that requiring thermal leptogenesis forces m1 < 3e-2 eV, the KATRIN testability angle, and the proton decay branching ratio bound BR(p -> pi0 mu+) < 30% in the compatible region. As a summary, it is clear and honest about where things come from.\n\nThe paper does a good job at laying out the model, the radiative seesaw structure, and the three distinct parameter domains (A, B, C) where the observed baryon asymmetry can be reproduced. The citation to their own prior work is appropriate — the heavy lifting is in Ref. [12] — and they are explicit that the result comes from a ULYSSES scan. That is real, reproducible work, even if it is not reproduced here.\n\nNow the soft spots. The biggest one is the assumption that thermal leptogenesis is the primary source of B-L. They acknowledge it in Sec. 2.1 but do not quantify it. The stress-test concern is fair: U(1)_X breaking at M_GUT can generate a net B-L before the seesaw scale, and with the seesaw scale radiatively generated around 1e8 GeV there is a large window where such an asymmetry can survive, especially in Domain A where washout is suppressed. The escape clauses — strong washout or suppressed CP asymmetry in heavy triplet decays — are not demonstrated for the parameter regions that give the quoted bound. So the m1 limit is a model prediction only under an additional, untested assumption. The paper says this, but the abstract and conclusions state the limit more baldly than the text justifies.\n\nA second, smaller issue: the abstract and Sec. 2.4 present the limit as an absolute neutrino mass bound, but Fig. 2 and the surrounding text specify a compressed, normally ordered spectrum with m1 around 3e-2 eV. The normally-ordered-only caveat should be carried through the summary. That is an overclaim, though easy to fix.\n\nWho is this for? GUT phenomenologists and neutrino model builders who want a quick pointer to what the flipped SU(5) radiative seesaw can do, and KATRIN watchers. It is not a standalone research paper; if it were submitted as one, I would desk reject it because the content is a summary. As a proceedings contribution, it is acceptable once the caveats above are added. For your own reading, cite the PRD, not this proceedings.","headline":"Useful proceedings summary of the authors' own PRD scan; the m1 bound is real but conditional on an unquantified thermal-leptogenesis-dominance assumption, and the abstract overstates it.","tokens_in":6803,"tokens_out":2460,"would_cite":false,"duration_ms":30139,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":false},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["12.10.Dm","14.60.Pq","98.80.Cq"],"model":"deepseek-v4-flash","headline":"The paper claims that in the minimal flipped $SU(5)$ model, reproducing the cosmic baryon asymmetry by thermal leptogenesis requires the lightest neutrino mass below about $3\\times10^{-2}$ eV, making the model testable in beta-decay and…","keywords":["baryogenesis","leptogenesis","flipped SU(5)","radiative seesaw","neutrino mass","proton decay","KATRIN","grand unified theories"],"falsifier":"Measure the effective electron-neutrino mass $m_\\beta$ in $\\beta$ decay or the sum of neutrino masses $\\sum m_\\nu$ in cosmology. If the data require the lightest active neutrino mass to be above $3\\times10^{-2}$ eV, the model cannot produce the observed baryon asymmetry, given the stated assumption that thermal leptogenesis is the primary source of $B-L$. Alternatively, observe proton decay with $\\mathrm{BR}(p\\to\\pi^0\\mu^+) > 30\\%$, which no point in the $\\eta_B$-compatible region allows.","tokens_in":5709,"feed_emoji":"⚛️","tokens_out":12436,"duration_ms":112868,"temperature":0.7,"pith_summary":"This paper examines whether the minimal flipped $SU(5)$ grand unified theory with radiatively generated right-handed neutrino masses can explain the observed matter-antimatter asymmetry of the Universe through thermal leptogenesis. It reports that imposing successful leptogenesis as an extra condition on the model's already tightly constrained flavour structure forces the lightest active neutrino mass below about $3\\times10^{-2}$ eV, regardless of which of the three viable production regimes is at work. If correct, this is a testable prediction: the bound translates into an effective neutrino mass within reach of the KATRIN $\\beta$-decay experiment, and into a universal upper bound of $30\\%$ on the $p\\to\\pi^0\\mu^+$ proton decay branching ratio. The paper therefore turns the baryon asymmetry from a given into a sharp constraint that can distinguish the model.","feed_headline":"Baryon asymmetry pins lightest neutrino below 0.03 eV","feed_subtitle":"Matching the cosmic matter asymmetry forces the lightest neutrino below 3e-2 eV and sharpens proton-decay predictions.","key_machinery":"The load-bearing structure is the correlation between the Dirac neutrino Yukawa matrix and the up-quark mass matrix, $M_D^\\nu = M_u^T$, combined with the two-loop radiative generation of the right-handed neutrino Majorana masses. Because the model has no tree-level source of those masses, the heavy spectrum is tied to the charged-fermion sector and to perturbativity and non-tachyonicity bounds. The mass relation $m_1 m_2 m_3 M_1 M_2 M_3 = m_u^2 m_c^2 m_t^2 \\sim 1.3\\ \\mathrm{GeV}^6$ links the light and heavy neutrino spectra, and a numerical evaluation of the baryon-to-photon ratio $\\eta_B$ over the parameter space shows that $\\eta_B \\approx 6\\times10^{-10}$ is attainable only for $m_1 \\lesssim 3\\times10^{-2}$ eV. The same scan fixes the unitary matrix $U_\\nu$ connecting neutrino and quark sectors, which enters the two-body proton decay amplitudes such as $\\Gamma(p\\to\\pi^0\\mu^+) \\propto |(V_{\\mathrm{PMNS}}U_\\nu)_{21}|^2$.","core_discovery":"The paper's central claim is that in the minimal flipped $SU(5)$ theory, where the right-handed neutrino Majorana masses arise at two loops and the Dirac neutrino Yukawa matrix is tied to the up-quark mass matrix, the observed baryon-to-photon ratio $\\eta_B \\approx 6\\times10^{-10}$ is reproduced only when the lightest active neutrino mass $m_1$ lies below about $3\\times10^{-2}$ eV. This holds across all three leptogenesis regimes the authors distinguish: lightest right-handed neutrino ($N_1$)-dominated production, $N_2$-dominated production protected from washout, and hierarchical spectra kept alive by suppressed decoherence. The constraint follows from the mass relation $m_1 m_2 m_3 M_1 M_2 M_3 = m_u^2 m_c^2 m_t^2 \\sim 1.3\\ \\mathrm{GeV}^6$ and the two-loop suppression which together push the heavy spectrum toward the lower bound on the lightest right-handed neutrino mass required for successful leptogenesis. As a result, the effective neutrino mass in $\\beta$ decay is bounded at a level relevant for KATRIN, and the proton decay branching ratio into $\\pi^0\\mu^+$ never exceeds $30\\%$ in the $\\eta_B$-compatible region.","pith_inferences":["If future cosmology (for instance, CMB measurements of $\\sum m_\\nu$) settles the lightest neutrino mass above $3\\times10^{-2}$ eV, the paper's assumption of thermal leptogenesis dominance would be pressed, and the model would need an additional source of $B-L$ above the seesaw scale.","The same logic could be applied to other grand unified models with strong correlations between heavy right-handed neutrino and fermion mass matrices; those models may inherit analogous upper bounds on the absolute neutrino mass once baryogenesis is imposed.","The boundary at $m_1\\sim3\\times10^{-2}$ eV is a fine-tuned corner: a future positive signal near that value in a KATRIN-like experiment would force the model into a narrow, strongly constrained parameter region, making nearby observables like lepton-flavour-violating decays sharper tests.","A combined measurement strategy could pair beta-decay and proton-decay searches: finding muon-channel proton decay with a branching ratio above $30\\%$ would falsify the region that reproduces the baryon asymmetry under the paper's assumptions, whereas a low $m_\\beta$ together with absence of such a signal would support it."],"forward_implications":["The observed baryon asymmetry can be reproduced in three distinct regimes — decays of the lightest right-handed neutrino, decays of the next-to-lightest one with suppressed washout, and hierarchical spectra with strongly suppressed decoherence — so the model is not excluded by generic lower bounds on the heavy neutrino mass.","The absolute neutrino mass scale is bounded by $m_1 < 3\\times10^{-2}$ eV, which translates into an upper limit on the effective beta-decay mass $m_\\beta$ at a level that ongoing experiments such as KATRIN can probe.","In the baryogenesis-compatible region, the proton decay branching ratio satisfies $\\mathrm{BR}(p\\to\\pi^0\\mu^+) < 30\\%$, and the bound tightens to about $10\\%$ when $m_1$ drops near $10^{-3}$ eV.","The heavy neutrino spectrum in the compatible region is at least mildly degenerate, with masses peaking near $10^{8.8}$ GeV, which distinguishes the scenario from generic hierarchical seesaw models.","If the prediction survives experimental scrutiny, the minimal flipped $SU(5)$ with radiative seesaw would simultaneously account for neutrino masses, proton decay patterns, and baryogenesis."],"supporting_citations":[{"why":"Supplies the dedicated parameter-space scan of the model and the three leptogenesis domains from which the $m_1 < 3\\times10^{-2}$ eV bound is extracted.","marker":"[12]"},{"why":"Establishes the two-loop radiative seesaw mechanism for right-handed neutrino Majorana masses and the charged-fermion correlation on which the analysis builds.","marker":"[3]"},{"why":"Defines the thermal leptogenesis mechanism that the paper assumes to be the primary source of the net $B-L$ asymmetry.","marker":"[13]"},{"why":"Provides the lower bound on the lightest right-handed neutrino mass for successful leptogenesis, the obstacle the models' regimes must circumvent.","marker":"[17]"},{"why":"Supplies the numerical package used to compute the baryon-to-photon ratio $\\eta_B$ across the scanned parameter space.","marker":"[18]"},{"why":"Gives the KATRIN experiment's neutrino mass reach, which determines that the derived $m_1$ bound is testable in current beta-decay searches.","marker":"[16]"}],"fun_headline_variants":["Leptogenesis caps lightest neutrino below 0.03 eV","Baryon asymmetry pins m1 below 0.03 eV","Flipped SU(5) forces neutrino mass ceiling below 0.03 eV","KATRIN-relevant bound: m1 under 0.03 eV from leptogenesis","Cosmic asymmetry narrows neutrino mass to under 0.03 eV"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The paper assumes that no comparable baryon-minus-lepton asymmetry is generated at or above the unification scale — for instance by decays of heavy colour triplets — so that thermal leptogenesis is the primary source of the net $B-L$ asymmetry; if an earlier source dominates, the computed $\\eta_B$ values and the $m_1 < 3\\times10^{-2}$ eV conclusion need not hold.","fun_headline_variants_meta":{"raw":{"variants":["Leptogenesis caps lightest neutrino below 0.03 eV","Baryon asymmetry pins m1 below 0.03 eV","Flipped SU(5) forces neutrino mass ceiling below 0.03 eV","KATRIN-relevant bound: m1 under 0.03 eV from leptogenesis","Cosmic asymmetry narrows neutrino mass to under 0.03 eV"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000945,"raw_usage":{"total_tokens":4060,"prompt_tokens":996,"completion_tokens":3064,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":612,"completion_tokens_details":{"reasoning_tokens":2962}},"tokens_in":612,"tokens_out":3064,"duration_ms":23015,"temperature":1.0,"reasoning_tokens":2962,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T21:48:34.464239+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the effective electron-neutrino mass $m_\\beta$ in $\\beta$ decay or the sum of neutrino masses $\\sum m_\\nu$ in cosmology. If the data require the lightest active neutrino mass to be above $3\\times10^{-2}$ eV, the model cannot produce the observed baryon asymmetry, given the stated assumption that thermal leptogenesis is the primary source of $B-L$. Alternatively, observe proton decay with $\\mathrm{BR}(p\\to\\pi^0\\mu^+) > 30\\%$, which no point in the $\\eta_B$-compatible region allows.","supporting_citations":[{"cited_title":"Leptogenesis in the minimal flipped $SU(5)$ unification","cited_arxiv_id":"2312.08357","evidence_quote":"Supplies the dedicated parameter-space scan of the model and the three leptogenesis domains from which the $m_1 < 3\\times10^{-2}$ eV bound is extracted."}],"review_version":1}