{"id":"7b2c695e-caff-4ada-a692-35de732a61fe","arxiv_id":"2412.12210","paper_version":2,"verdict":"REJECT","confidence":"MODERATE","novelty_score":3.0,"correctness_risk":"high","formal_verification":"none","parameter_count":5,"one_line_summary":"A two-parameter jerk-based f(Q,T) model is fit to OHD and Pantheon data, but the Pantheon H0 constraints are artifacts and the ekpyrotic pre-Big-Bang phase is an interpretation mismatch.","lead":"This paper constructs a flat f(Q,T) gravity model, fits two parameters to Hubble and supernova data, and reports a deceleration-to-acceleration transition, a high-redshift 'ekpyrotic' phase, and a reduced Hubble constant tension. The supernova fitting appears to contain a serious error, and the early-universe brane collision interpretation is not supported by the model's equations.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The Pantheon likelihood in Eqs. (24)-(27) is independent of H0 because H0 cancels exactly in the distance modulus, so the H0 values in Table II and the claimed H0-tension reduction are not supported by the data.","rationale":"The reader's formal weakest_assumption is the ad hoc jerk ansatz, but the reader's rationale also notes the H0 cancellation in the distance modulus. I identify the H0 cancellation as the single most load-bearing concern because it is a direct algebraic contradiction between the equations the paper writes and the constraints it reports. It does not depend on judging model assumptions; it can be checked by substitution. It also explains why a 1048-point supernova sample without an absolute-magnitude calibration cannot produce a 10^-4 H0 constraint. Since Table II, the abstract, and Section V all rely on these H0 values, the REJECT verdict is reinforced rather than changed.","tokens_in":21543,"tokens_out":4140,"duration_ms":36039,"concrete_test":"Recompute ∂μ_th/∂H0 from Eqs. (22), (24)-(27) at fixed α and show that it is identically zero for every Pantheon datum; then rerun the Pantheon-only MCMC with a wide flat prior on H0 (e.g., 40-100 km/s/Mpc) and an unconstrained absolute magnitude, and check whether the H0 posterior is flat. If it is flat, the Table II Pantheon and joint H0 errors can only originate from an unspecified prior or a bug, and the H0-tension claim is void.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim is that OHD+Pantheon constrains H0 = 69.99999 ± 0.0001 and thereby reduces the H0 tension. This claim fails at the level of the likelihood written in the paper. With Eq. (22) written as H(z) = H0 f(z), the luminosity distance is D_L(z) = (1+z)c ∫_0^z dz'/H(z') = H0^{-1}(1+z)c ∫_0^z dz'/f(z'), so every D_L term is proportional to H0^{-1}. Eq. (24) is μ = 5 log10 D_L + μ0, and Eq. (26) is μ0 = 5 log10(H0^{-1}/1 Mpc) + 25 = -5 log10 H0 + constant. Thus μ = 5 log10[(1+z)c ∫ dz'/f(z')] + constant - 5 log10 H0 - 5 log10 H0, and the two H0-dependent terms cancel: μ is exactly independent of H0. Consequently χ²_PDS in Eq. (27) cannot constrain H0 at all. The Pantheon-only row in Table II (69.99998 ± 0.0001) and the joint row (69.99999 ± 0.0001) with 10^-4 uncertainties must therefore come from an unspecified prior, a numerical artifact, or an error in the MCMC implementation described in Sect. III. Because the abstract and Section V base the H0-tension-reduction conclusion on exactly these numbers, that central claim collapses, independently of the additional ad hoc nature of the jerk ansatz Eq. (18).","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper constructs a flat FLRW cosmological model in f(Q,T) gravity with f(Q,T)=ζQ²+γT. The dynamical expansion history is not obtained from the f(Q,T) field equations; instead the authors assume a kinematic jerk ansatz, j(z)=e^{q(z)}≈1+q(z)+q²(z)/2, solve the resulting differential equation for q(z), and integrate to obtain H(z). They then fit the free parameters α and H0 to the OHD, Pantheon, and joint datasets, and use the fitted H(z) to compute ρ, p, the equation of state, energy conditions, a quintessence-like scalar field, and slow-roll parameters. The paper claims a deceleration-to-acceleration transition, a quintessence phase at late times, an ekpyrotic phase at z>12.32 in which the Big Bang is a brane collision, and a reduction of the H0 tension with H0≈70.0 from the joint fit.","tokens_in":21935,"tokens_out":9691,"duration_ms":88951,"significance":"If the claims were valid, the paper would show that a specific f(Q,T) gravity model can fit the background expansion history and, through the recovered H0≈70 km/s/Mpc, mitigate the Hubble tension. The manuscript has some strengths: the field equations are written out explicitly, the algebraic derivation of ρ and p from the assumed H(z) is transparent, public OHD and Pantheon data are used, and comparisons with ΛCDM and several other modified-gravity models are provided. However, the central results are not supported. The expansion history is fixed by an ad hoc jerk ansatz rather than by the modified-gravity dynamics; the Pantheon likelihood as written cannot produce the reported H0 constraints; the coupling constants ζ and γ are set by hand; and the ekpyrotic and slow-roll interpretations rest on conceptual misapplications. These issues affect the paper's main quantitative and qualitative conclusions, not merely their presentation.","major_comments":[{"comment":"The Pantheon likelihood cannot support the H0 values reported in Table II. Writing H(z)=H0 f(z), Eq. (25) gives D_L=(1+z)c∫dz'/H = H0^{-1}(1+z)c∫dz'/f, so D_L is proportional to H0^{-1}. Equation (26) then introduces a second H0^{-1} factor through μ0. Read literally, the two H0 factors do not cancel; they enter as −5log10H0 and −5log10H0, so the resulting χ²_PDS is a double-counted, dimensionally inconsistent function of H0. If, instead, the intended convention is the standard one in which H0 appears only in μ0, then the Pantheon sample with an uncalibrated absolute magnitude cannot constrain H0 at all. In either reading, the Pantheon-only value H0=69.99998±0.0001 and the joint value H0=69.99999±0.0001 are not supported by the written likelihood. Since the abstract and Section V base the claimed H0-tension reduction on exactly these numbers, this is a load-bearing error.","section":"III, Eqs. (24)–(27); Table II"},{"comment":"The expansion history H(z) is not derived from the f(Q,T) field equations. The paper assumes j(z)=e^{q(z)} and then approximates it by 1+q+q²/2, solves the resulting differential equation for q(z), and integrates to get H(z) in Eq. (22). The field equations (14)–(17) are used only afterward, to convert this assumed H(z) into ρ and p. Consequently, the deceleration-to-acceleration transition redshifts, the equation-of-state phases, the ekpyrotic boundary z>12.32, and the quintessence behavior are properties of the assumed jerk ansatz and the fitted α, not independent predictions of f(Q,T) gravity. The abstract and Section V present these quantities as outcomes of the constrained f(Q,T) model, which is not justified by the derivation.","section":"II, Eq. (18) and the paragraph after it"},{"comment":"The coupling constants ζ and γ are fixed by hand, with ζ=−1.82 and γ=−0.9 used in Fig. 4, and they are never constrained by the data or derived from any theoretical condition. All of the derived physical quantities—ρ, p, ω, the energy conditions, and the scalar-field kinetic and potential terms—depend on these arbitrary values through Eqs. (16) and (17). The qualitative conclusions, including the claimed ekpyrotic phase and quintessence phase, are therefore not robust predictions of a constrained model. The paper should either constrain ζ and γ jointly or demonstrate that the conclusions are insensitive to their values over a well-motivated range.","section":"IV, Fig. 4 caption; III, Table II"},{"comment":"The identification of an ekpyrotic phase is not supported by the model. The ekpyrotic scenario (ref. [55]) involves a slow contraction phase before the Big Bang, with the Big Bang described as a brane collision. In this paper, H(z) from Eq. (22) is positive for all z≥0, describing an expanding universe, and the model contains no contracting branch or brane-collision dynamics. The appearance of ω≫1 at high redshift in an expanding FLRW model does not constitute an ekpyrotic phase, and the statement that 'the Big Bang is not the beginning of time' is an extrapolation from the assumed EoS rather than a consequence of the f(Q,T) equations.","section":"IV, Table III and Fig. 4c"}],"minor_comments":[{"comment":"Equation (26) is dimensionally inconsistent: H0^{-1} has units of time (or Mpc s/km), not Mpc, and the combination 5Log10(H0^{-1}/1Mpc)+25 mixes units. The standard route is to define a dimensionless reduced luminosity distance d_L=(1+z)∫dz'/E(z') and set μ0=5log10(c/H0/Mpc)+25.","section":"III, Eq. (26)"},{"comment":"The Pantheon and joint H0 uncertainties of about 10^-4 km/s/Mpc are implausibly small and, together with the near-exact value 69.99999, suggest a numerical artifact. The authors should report the MCMC chains, a check with H0 fixed, or a marginalized likelihood for H0.","section":"III, Table II"},{"comment":"The slow-roll parameters are evaluated in the limit z→−1, which is the far future in this redshift coordinate, not the early-universe inflationary regime. The statement that the model 'solves the horizon and flatness problems' is therefore unsupported by the shown behavior of ϵ1 and ϵ2.","section":"IV.C, Fig. 7"},{"comment":"The quintessence interval is written as −1/3>ω>−1, which is reversed; it should be −1<ω<−1/3. The notation ω>>1 should be ω≫1.","section":"IV, Table III"},{"comment":"There are numerous typographical and phrasing errors, e.g., 'P antheon', 'alikeness', 'the EoS traverses from positive to negative, which tends to −1', and the erratic spacing in 'f (Q, T)'. A careful editorial pass is needed.","section":"Throughout"}],"recommendation":"reject","confidential_remarks":"The central statistical claim fails at the level of the written likelihood, and the dynamical content is not derived from the f(Q,T) field equations. The arbitrary choice of ζ and γ and the misapplication of the ekpyrotic and slow-roll concepts compound the problem. I do not see a modest revision that would make the paper publishable; a fundamental rewrite and a new statistical analysis would be required."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take on 2412.12210. The paper's headline—that a constrained f(Q,T) model reduces the H0 tension to 69.99999 ± 0.0001—is not credible, but not for the reason in the stress test. The stress test claims H0 cancels in the distance modulus. It doesn't: with μ = 5 log10 D_L + μ0 and μ0 = 5 log10(H0^{-1}) + 25, and D_L ∝ H0^{-1}, the H0 terms add, giving -10 log10 H0. The likelihood does depend on H0, but the formula double-counts it. That, combined with a fixed α, is probably why the MCMC spits out 10^-4 uncertainties. The real problem is that the expansion history is not derived from the f(Q,T) field equations; it is set by an assumed jerk function j = 1 + q + q²/2 (from a Maclaurin expansion of exp(q)). The field equations are then only used to compute ρ and p. So the \"constraints\" test the jerk ansatz, not the gravity theory.\n\nWhat is useful: the authors carry through a complete analytic treatment—exact H(z), ρ(z), p(z), a scalar-field description, slow-roll parameters, energy conditions—and compare against OHD and Pantheon in a standard way (modulo the H0 double-count). For a reader who wants to see the machinery of f(Q,T) cosmology applied to a kinematical ansatz, it is a reasonable template. The table comparing H0 across modified gravity models is a handy summary.\n\nSoft spots beyond the likelihood: the ekpyrotic claim is a mislabel. The model has an expanding universe with ω >> 1 at high z; there is no contracting branch, so calling it ekpyrotic (and the brane-collision Big Bang) is importing Lehners's scenario without the dynamics. The slow-roll analysis evaluates ε1, ε2 at z → -1, the far future, and calls it inflation; inflation should be at early times. Those two interpretive steps are the paper's main scientific overreach.\n\nWho it's for: people working in f(Q,T) phenomenology, maybe as a baseline for a better likelihood treatment. I would not cite it. It deserves a referee—the errors are specific and fixable—but the referee will likely ask for a corrected likelihood, a reframing that does not claim to constrain f(Q,T), and removal or justification of the ekpyrotic and inflation interpretations. If they fix those, there might be a modest paper here.","headline":"An analytically complete but kinematically driven f(Q,T) paper whose H0-tension claim is spoiled by a double-counted likelihood and whose ekpyrotic/inflationary interpretations are overstated.","tokens_in":22471,"tokens_out":7524,"would_cite":false,"duration_ms":59336,"reading_group":"no","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":["83D05","83F05"],"pacs":["98.80.Cq"],"model":"deepseek-v4-flash","headline":"A constrained f(Q,T) gravity model claims to ease the Hubble tension and to replace the Big Bang singularity with an ekpyrotic brane collision.","keywords":["f(Q,T) gravity","non-metricity gravity","Hubble tension","ekpyrotic phase","quintessence","jerk parameter","deceleration-to-acceleration transition","Pantheon dataset"],"falsifier":"Solve the f(Q,T)=ζQ²+γT field equations directly for H(z) without the jerk ansatz, using the same ζ=-1.82, γ=-0.9 and the same likelihoods, and compare the best-fit H0 and transition redshift with the paper's values; alternatively, measure the jerk parameter j(z) from an independent high-redshift cosmic-chronometer or BAO sample and check whether it equals 1+q+q²/2. A mismatch would settle that the claimed H0 value and the ekpyrotic phase are artifacts of the assumed ansatz rather than consequences of f(Q,T) gravity.","tokens_in":21302,"feed_emoji":"🌌","tokens_out":6356,"duration_ms":57317,"temperature":0.7,"pith_summary":"The paper tries to establish that a specific quadratic f(Q,T) gravity model, with f(Q,T)=ζQ²+γT, can reproduce the observed expansion history once one assumes a particular form for the jerk parameter. Fitting to 77 cosmic-chronometer H(z) points and 1048 Pantheon supernovae gives H0=69.99999±0.0001, a middle value that the authors say reduces the Hubble tension. The same model yields an ekpyrotic pre-Big-Bang phase above redshift z=12.32 and a late-time quintessence phase, so a single modified-gravity function would connect the H0 tension, the origin of the universe, and cosmic acceleration without a cosmological constant. The key caveat, stated in the construction, is that the expansion history is imposed by the jerk ansatz rather than solved from the field equations.","feed_headline":"H0 lands at 70 in a gravity model with an ekpyrotic prelude","feed_subtitle":"One quadratic gravity model yields H0 near 70, easing the Hubble tension, and a brane-collision origin.","key_machinery":"The load-bearing object is the kinematic jerk ansatz: Eq. (18) defines j(z)=q(z)+2q(z)²+(1+z)dq/dz, and the paper sets j(z)=1+q(z)+q²(z)/2, the first three Maclaurin terms of e^q. Solving this first-order differential equation yields q(z), and then the relation q(z)=-1+(1+z)(dH/dz)/H gives the closed-form Hubble parameter H(z) shown in Eq. (22). The f(Q,T) action with f=ζQ²+γT (n=2, m=1) supplies the generalized Friedmann equations that convert this H(z) into energy density and pressure, and all subsequent results—transition redshifts, energy conditions, scalar-field potentials, slow-roll parameters—are read off those expressions.","core_discovery":"The paper claims that in flat FLRW spacetime within f(Q,T) gravity, taking f(Q,T)=ζQ²+γT and choosing the jerk parameter as j(z)=1+q(z)+q²(z)/2 fully determines the deceleration and Hubble parameters. Constraining the two free constants with the OHD and Pantheon datasets gives H0=69.99999±0.0001 from the joint fit, a value the authors interpret as easing the H0 tension when compared with other modified-gravity results and with ΛCDM. The same kinematics produces an equation of state ω>>1 at z>12.32, which the authors identify with an ekpyrotic contracting phase whose Big Bang is a brane collision rather than the beginning of time, and a late-time phase with -1<ω<-1/3, characterizing quintessence dark energy. The f(Q,T) field equations are used not to determine H(z) but to reconstruct ρ, p, energy conditions, scalar-field kinetic and potential terms, and slow-roll parameters from the assumed H(z).","pith_inferences":["Inference: because H(z) is fixed by the jerk ansatz rather than by the f(Q,T) dynamics, the same expansion history could be embedded in many gravity theories; the claimed H0 value likely tests the kinematic ansatz more than it tests f(Q,T) gravity itself.","Inference: replacing the ad hoc jerk form with a theoretically motivated one, for example from a scalar-tensor or effective-loop model, would provide a direct template for translating any j(z) into a full f(Q,T) cosmology and would show whether the ekpyrotic and quintessence phases survive.","Inference: the tiny reported error on H0 reflects fitting the chosen datasets with a two-parameter function, not cosmological certainty; adding BAO or CMB data could shift the central value and substantially enlarge the error bars.","Inference: a sharper observational test is to compare the predicted very early transition redshift and the pressure sign-change redshift with independent tracers of the matter-to-acceleration crossover; standard dark-energy probes would likely constrain such an early transition if it is not specific to the Pantheon sample."],"forward_implications":["The joint OHD+Pantheon fit pins H0 at 69.99999 with sub-0.0002 reported errors, a value between CMB and local distance-ladder estimates, which the authors take as easing the Hubble tension.","The model predicts a deceleration-to-acceleration transition at ztr=6.39 for the joint dataset, much earlier than the standard ΛCDM transition near z≈0.6, so it makes a distinctive prediction for future high-redshift probes.","At z>12.32 the equation of state satisfies ω>>1, interpreted as an ekpyrotic phase with a brane-collision 'Big Bang', meaning the initial singularity is not the beginning of time in this model.","At late times the model behaves as quintessence with -1<ω<-1/3 and violates the strong energy condition, consistent with present-day cosmic acceleration without a cosmological constant.","The model deviates from ΛCDM at early times (j does not equal 1) but converges to ΛCDM behavior at late times in the H(z) and distance-modulus plots."],"supporting_citations":[{"why":"Supplies the f(Q,T) action and field equations that give the generalized Friedmann equations used to reconstruct ρ and p.","marker":"[81]"},{"why":"Cited as motivating the choice n=2 and m=1 in f(Q,T)=ζQ^n+γT^m, i.e., the quadratic form used in the model.","marker":"[82]"},{"why":"Source of the ekpyrotic and cyclic mechanism in which the Big Bang is described as a collision of branes, the basis for the z>12.32 interpretation.","marker":"[55]"},{"why":"Underlies the Pantheon sample's 1048 supernova points listed in Table I, one of the two datasets constraining α and H0.","marker":"[95]"},{"why":"Provides the precedent of parametrizing the jerk parameter to construct cosmological models, supporting the paper's j(z) ansatz.","marker":"[93]"},{"why":"Another jerk-parametrization precedent used to justify choosing j(z) and solving the differential equation for q(z).","marker":"[94]"},{"why":"Gives the f(R,T) H0 fit used in Table V as a comparison value for the claimed H0-tension reduction.","marker":"[25]"},{"why":"Gives another f(R,T) H0 fit used in Table V as a comparison value for the claimed H0-tension reduction.","marker":"[34]"}],"fun_headline_variants":["Modified gravity eases Hubble tension, hints brane-collision start","Quadratic f(Q,T) model yields H0=70 and pre-Bang ekpyrosis","Gravity model: H0=70, no Big Bang singularity, just brane clash","Ekpyrotic bounce instead of Big Bang? H0=70 in new f(Q,T) model","Constrained f(Q,T) gravity gives H0=70, hints at ekpyrotic prelude"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The expansion history is imposed by choosing the jerk parameter to be 1+q+q²/2; the f(Q,T) field equations never determine H(z), so every result—the fitted H0, the transition redshift, the ekpyrotic and quintessence phases—rests on that untested kinematic choice.","fun_headline_variants_meta":{"raw":{"variants":["Modified gravity eases Hubble tension, hints brane-collision start","Quadratic f(Q,T) model yields H0=70 and pre-Bang ekpyrosis","Gravity model: H0=70, no Big Bang singularity, just brane clash","Ekpyrotic bounce instead of Big Bang? H0=70 in new f(Q,T) model","Constrained f(Q,T) gravity gives H0=70, hints at ekpyrotic prelude"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00067,"raw_usage":{"total_tokens":3105,"prompt_tokens":1045,"completion_tokens":2060,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":661,"completion_tokens_details":{"reasoning_tokens":1943}},"tokens_in":661,"tokens_out":2060,"duration_ms":15786,"temperature":1.0,"reasoning_tokens":1943,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T15:05:37.186718+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Solve the f(Q,T)=ζQ²+γT field equations directly for H(z) without the jerk ansatz, using the same ζ=-1.82, γ=-0.9 and the same likelihoods, and compare the best-fit H0 and transition redshift with the paper's values; alternatively, measure the jerk parameter j(z) from an independent high-redshift cosmic-chronometer or BAO sample and check whether it equals 1+q+q²/2. A mismatch would settle that the claimed H0 value and the ekpyrotic phase are artifacts of the assumed ansatz rather than consequences of f(Q,T) gravity.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the f(Q,T) action and field equations that give the generalized Friedmann equations used to reconstruct ρ and p."},{"cited_title":"Gadbail, S","cited_arxiv_id":null,"evidence_quote":"Cited as motivating the choice n=2 and m=1 in f(Q,T)=ζQ^n+γT^m, i.e., the quadratic form used in the model."},{"cited_title":"Kofinas and E","cited_arxiv_id":null,"evidence_quote":"Underlies the Pantheon sample's 1048 supernova points listed in Table I, one of the two datasets constraining α and H0."},{"cited_title":"Golovnev and M","cited_arxiv_id":null,"evidence_quote":"Provides the precedent of parametrizing the jerk parameter to construct cosmological models, supporting the paper's j(z) ansatz."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Another jerk-parametrization precedent used to justify choosing j(z) and solving the differential equation for q(z)."}],"review_version":1}