{"id":"d8b5b53b-f6cb-4572-844c-b8ff76593dc5","arxiv_id":"2412.09568","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"A one-parameter modification that lets gravity differ above and below the Hubble scale fits CMB and BAO data with a preference for slightly weaker superhorizon gravity, at about 2 sigma.","lead":"Cosmological data prefer a small 'glitch' in gravity: on scales larger than the cosmic horizon, gravity appears about 0.6 to 0.9 percent weaker than on smaller scales, at roughly 2 sigma significance. A single-parameter extension of standard cosmology that allows this difference also softens two persistent tensions in modern cosmology: the Hubble tension and the clustering tension.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 2σ preference for Ωg rests on a PPF perfect-fluid treatment with c_s^2=1; if the actual Lorentz-violating theories have anisotropic stress or different perturbation dynamics, the fitted Ωg does not robustly map to G_cosmo/G_N.","rationale":"The reader's weakest_assumption identifies exactly the same load-bearing concern: the PPF perfect-fluid description with c_s^2 = 1 is an assumption that may not capture the perturbation dynamics of the Lorentz-violating theories. My read confirms this is the most important point, because the empirical 2σ preference for negative Ωg is obtained through this fluid model, and the interpretation in terms of G_cosmo/G_N depends on the accuracy of that mapping. The concern is substantive but not fatal: the paper clearly discloses the assumption, tests moderate variations of c_s^2, and presents the significance honestly. The absence of machine-checked proofs or released code increases the risk, but the statistical analysis itself is standard and the likelihoods are public. The BBN extrapolation and the logarithmic running to Planck and de Sitter scales are speculative, but they are explicitly framed as suggestive and are not required for the central CMB/BAO result. Therefore the paper deserves a conditional acceptance with the mapping concern flagged, which matches the reader's CONDITIONAL verdict; my stress-test does not change that assessment.","tokens_in":9091,"tokens_out":9341,"duration_ms":89476,"concrete_test":"Implement the exact linear perturbation equations of cuscuton (or Einstein-Aether) on the same CGG background with Ωg = -0.0087 in a public Einstein-Boltzmann solver (e.g., EFTCAMB or a modified CAMB) and compare the resulting low-ℓ CMB TT/TE/EE and lensing spectra with the PPF-fluid prediction at c_s^2 = 1. If the spectra differ by more than the Planck 2018 uncertainty (or by more than ~10% of the Ωg-induced signal), the fluid mapping is inadequate and the reported constraint on G_cosmo/G_N is not robust.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that CMB and BAO data favor a single-parameter model with weaker superhorizon gravity, quantified as Ωg = -0.0087 ± 0.0046 (Planck18) or -0.0059 ± 0.0027 (combined). The constraint is derived by modifying CAMB and 'treat[ing] the CGG component as a perfect fluid at the linear perturbation level... with c_s^2 = 1' (Section 2, PPF framework). This fluid description is the essential bridge between the observed ISW signal and the inferred value of G_cosmo/G_N: at the background level Eq. (4) exactly maps Ωg to G_N/G_cosmo, but the CMB power spectrum, especially at low ℓ, depends on the perturbation equations, not just the background. A minimally coupled perfect fluid with c_s^2 = 1 is one particular choice; the Lorentz-violating theories that motivate CGG (cuscuton, Hořava-Lifshitz, Einstein-Aether) generally possess anisotropic stress (Φ ≠ Ψ), nonstandard propagation speeds, and in the cuscuton case an effectively infinite sound speed rather than c_s^2 = 1. The PPF double-field prescription is designed for phenomenological dark energy with arbitrary w and c_s, not for the full linearized Einstein equations of these modified gravity theories. The paper's robustness check varying c_s^2 between 0.1 and 10 changes only one parameter and does not test anisotropic stress or the functional form of the perturbation equations. If the true perturbation dynamics differ, the fitted Ωg is biased and the reported G_cosmo/G_N = 0.9914 ± 0.0045 would not correspond to the actual strength of superhorizon gravity. This is the load-bearing step for the paper's main interpretation.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper studies a single-parameter extension to ΛCDM, the 'cosmic glitch in gravity' (CGG) model, in which the Friedmann equation is modified by Ω_g = 1 − G_N/G_cosmo and reformulated as an effective dark-energy component. The authors modify CAMB, use the PPF double-field prescription with c_s^2 = 1, and run PolyChord/Cobaya nested sampling against Planck18, Planck PR4, BAO (Stage-III and DESI Y1), Pantheon+ SNe, DES Y1, and SH0ES. They report Ω_g = −0.0087 ± 0.0046 for Planck18, corresponding to G_cosmo/G_N = 0.9914 ± 0.0045, and Ω_g = −0.0067 ± 0.0029 for PR4+DESI Y1 BAO, with a combined 'All' value of Ω_g = −0.0059 ± 0.0027. They further report that the model eases the H0 tension from 4.1σ to 3.0σ and partly reconciles DES and Planck in the S8–Ωm plane, and they connect the negative Ω_g to a BBN value from EMPRESS, suggesting a logarithmic running.","tokens_in":9460,"tokens_out":7640,"duration_ms":72389,"significance":"If the CMB/BAO preference is real, the CGG model would be an economical hint that gravitational strength differs on super- and sub-horizon scales, and the forecast that Stage-IV data can reach σ(Ω_g) < 10^−3 is a falsifiable prediction. The paper follows standard Bayesian parameter estimation, reports robustness checks on c_s^2, and is transparent about the modest significance of the preference. The main caveat is that the fitted Ω_g is interpreted as G_cosmo/G_N through an assumed perfect-fluid description; without validation against the linear perturbation equations of the motivating Lorentz-violating theories, the claim is a phenomenological fit rather than a test of those theories.","major_comments":[{"comment":"The mapping from the CGG fluid to the fitted parameter is load-bearing and assumed rather than derived. The CMB constraint, especially the ISW signal at low ℓ, depends on the perturbation equations: Eq. (4) fixes the background relation, but the likelihood also depends on how the glitch fluid fluctuates. The paper assumes a single perfect fluid with c_s^2 = 1 in the PPF double-field prescription. The motivating theories (cuscuton, Hořava-Lifshitz, Einstein-Aether) have nonstandard sound speeds, anisotropic stress, and in some cases no propagating scalar, so the PPF fluid need not reproduce their linearized dynamics. The c_s^2 ∈ {0.1, 1, 10} check in Section 3 varies one parameter and does not test anisotropic stress or the functional form of the perturbation equations. Please either implement the actual perturbation equations for at least one concrete theory and show that they reduce to the fluid limit, or restrict the interpretation to a phenomenological fluid and do not identify Ω_g with G_cosmo/G_N.","section":"Section 2, PPF implementation"},{"comment":"The claimed logarithmic running is not supported by the analysis shown. There are exactly two independent constraints (BBN and CMB) and no fit of a scale-dependent law, no model comparison between constant Ω_g and running Ω_g, and no treatment of the extrapolation to Planck and de Sitter scales. As written, 'logarithmic running' is a speculative narrative, not a result of the paper. Please either add a quantitative fit of the scale dependence with uncertainties or explicitly label these lines as illustrative.","section":"Section 3.1, Fig. 3"},{"comment":"The 'All' constraint includes the SH0ES distance-ladder measurement, which is the same quantity used to define the Hubble tension the model claims to ease. Including SH0ES can pull Ω_g negative through the Ω_g–H0 degeneracy, so the tightest quoted value (−0.0059 ± 0.0027) is not an independent cosmological constraint. The central CMB+BAO preference is better represented by the Planck18+BAO or PR4+DESI rows; please report those as the primary result and treat the SH0ES-inclusive combination separately.","section":"Section 3.2, Table 2"}],"minor_comments":[{"comment":"The text refers to figures as 'in 1', 'in 3', and 'in 4' without figure numbers; please add the correct figure references.","section":"Figures throughout"},{"comment":"The prior range on Ω_g is not stated; please specify the uniform prior bounds used in PolyChord, since negative Ω_g regions and phantom-divide crossing can be sensitive to prior volume.","section":"Section 3"},{"comment":"The BBN value Ω_g = −0.085 ± 0.027 is taken from Ref. [21] and depends on the EMPRESS 4He measurement; given the active systematics debates around 4He abundances, one sentence noting this would be appropriate.","section":"Section 3.1"},{"comment":"The paper does not report Δχ² or Bayesian evidence for CGG over ΛCDM; the '2σ preference' would be easier to assess with such a quantity.","section":"Section 3"},{"comment":"The sentence beginning 'It can be rigorously shown...' with Ref. [8] is an important claim; consider spelling out which limits are meant (e.g., weak-field or Vainshtein) since the cited reference is not a standard modified-gravity review.","section":"Section 2"}],"recommendation":"major_revision","confidential_remarks":"This is a proceedings paper that largely reviews Ref. [1], with the main new elements being the PR4/DESI/DES likelihood updates and the BBN/running narrative. The 2σ detection is modest; my major concerns are about interpretation rather than the numerical pipeline. I would not require a full derivation of cuscuton/Hořava-Lifshitz/Einstein-Aether perturbation equations for a proceedings paper, but the authors should either supply a consistency check or weaken the G_cosmo/G_N interpretation."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read it. The genuinely new thing here is numerical: the same glitch model from their JCAP paper, now constrained with Planck PR4, DESI Y1, Pantheon+, DES Y1, and SH0ES, plus a Fisher forecast. That is an incremental but legitimate step. The analysis is competently done: nested sampling, explicit 1-sigma ranges, and an honest statement that the significance sits between 1.3 and 2.8 sigma depending on data. The Hubble-tension reduction from 4.1 to 3.0 sigma is modest and presented without spin.\n\nWhat I keep coming back to is the bridge between the fitted Omega_g and the claim about G_cosmo/G_N. Equation (4) is exact at the background level, but the CMB constraint, especially the low-ell ISW signal, depends on the perturbation equations. There the paper uses a perfect fluid with c_s^2 = 1 in the PPF framework. The motivating theories do not obviously reduce to that: cuscuton has an effectively infinite sound speed, and Horava-Lifshitz and Einstein-Aether carry anisotropic stress. Varying c_s^2 from 0.1 to 10 checks one parameter, not the functional form. So the fitted Omega_g is a phenomenological parameter tied to a particular perturbation prescription. The interpretation as a percent-level statement about superhorizon gravity is plausible but not as solid as the abstract implies.\n\nThe BBN part is imported: EMPRESS helium and a separate calculation by Kohri and Maeda. The 'logarithmic running' is a two-point extrapolation. The paper is mostly careful to call this speculative, but it is the weakest section.\n\nTwo smaller quibbles. The 'All' combination includes SH0ES, which folds the tension into the fit; it is transparent in Table 2, but I would not quote that row as a constraint. And the modified CAMB pipeline is not released, so the numbers are not independently checkable. That matters more for a paper whose content is new numbers.\n\nOverall: this deserves a serious referee. The core analysis is honest, the model is falsifiable, and the tension-easing claim is stated with its uncertainties. The referee should press on the perturbation mapping and ask for code/data release. I would not cite it in my own work in the next year, but I want it in the literature. Bring to reading group if you want to discuss what a 2-sigma cosmological hint is worth.","headline":"A competent, honest constraint update of the same glitch model, with a load-bearing fluid approximation that the authors do not fully defend.","tokens_in":10015,"tokens_out":3208,"would_cite":false,"duration_ms":31835,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Cosmic data favor gravity that is one percent weaker beyond the Hubble horizon.","keywords":["cosmic glitch","Lorentz violation","superhorizon gravity","Hubble tension","clustering tension","cosmic microwave background","baryon acoustic oscillations"],"falsifier":"Compute the CMB temperature power spectrum at $\\ell < 100$ directly from an explicit Einstein-Aether or cuscuton action at fixed $G_{\\rm cosmo}/G_N$; if the predicted integrated Sachs-Wolfe signal differs from the PPF perfect-fluid prediction by more than cosmic variance, the fitted $\\Omega_g$ is an artifact of the effective parametrization. A cosmic-variance-limited measurement of $\\Omega_g$ consistent with zero at $\\sigma < 10^{-3}$ would likewise remove the current preference.","tokens_in":8874,"feed_emoji":"🌌","tokens_out":11812,"duration_ms":93533,"temperature":0.7,"pith_summary":"This paper asks whether gravity could have a different strength on scales larger than the cosmological horizon than it does inside the horizon, and it shows that current cosmological data mildly prefer that it does. In a one-parameter extension of the standard cold-dark-matter model with a cosmological constant, the cosmic glitch parameter $\\Omega_g \\equiv 1 - G_N/G_{\\rm cosmo}$ measures how much superhorizon gravity differs from subhorizon gravity. Planck 2018 CMB data prefer $\\Omega_g = -0.0087 \\pm 0.0046$, and a combination of CMB, BAO including DESI Y1, supernova, lensing, and distance-ladder data gives $\\Omega_g = -0.0059 \\pm 0.0027$, a roughly $2\\sigma$ preference for weaker gravity. If the preference is real, the same parameter eases the Hubble tension from $4.1\\sigma$ to $3.0\\sigma$ and relaxes the $S_8$-$\\Omega_m$ clustering tension, and it connects to a stronger glitch during Big Bang nucleosynthesis.","feed_headline":"Cosmic data favor gravity 1 percent weaker beyond the Hubble horizon","feed_subtitle":"A single new parameter eases the Hubble and clustering tensions dividing today's cosmological surveys.","key_machinery":"The load-bearing object is the cosmic glitch parameter $\\Omega_g$ inserted into the Friedmann equation as $H^2 = (8\\pi G_N/3)(\\rho_{\\rm tot} + \\Omega_g \\rho_{\\rm crit})$, so the expansion rate responds to the total density with an effective gravitational strength $G_{\\rm cosmo} = G_N/(1-\\Omega_g)$. This one-number extension is the low-energy signature of Lorentz-violating gravity theories such as cuscuton, Hořava–Lifshitz, and Einstein-Aether, whose deviations from general relativity are screened below the Hubble scale. To predict the CMB, the glitch is treated as an additional perfect dark-energy fluid within the parameterized post-Friedmann (PPF) framework, with rest-frame sound speed $c_s^2 = 1$; the integrated Sachs-Wolfe effect at low multipoles (the temperature change CMB photons pick up crossing time-varying potentials) is the channel through which the data constrain $\\Omega_g$.","core_discovery":"The central claim is that the data favor a universe in which gravity is slightly weaker on superhorizon scales than on subhorizon scales, with the ratio encoded by $\\Omega_g \\equiv 1 - G_N/G_{\\rm cosmo}$. A fit to Planck 2018 gives $\\Omega_g = -0.0087 \\pm 0.0046$, i.e. $G_{\\rm cosmo}/G_N = 0.9914 \\pm 0.0045$; combining all datasets yields $\\Omega_g = -0.0059 \\pm 0.0027$. The preference remains at about the $2\\sigma$ level when the assumed dark-energy sound speed is varied from $c_s^2 = 0.1$ to $10$. The glitch also reaches back to Big Bang nucleosynthesis, where EMPRESS helium-abundance data require $\\Omega_g = -0.085 \\pm 0.027$, an order of magnitude stronger, which the authors interpret as evidence for a logarithmic running of the glitch with scale: maximum at the Big Bang, and nearly vanishing at the de Sitter radius of today's dark energy.","pith_inferences":["A direct test of the paper's mapping would be to evolve superhorizon perturbations in the full Einstein-Aether or cuscuton theory and compare the resulting CMB power at $\\ell < 100$ with the PPF perfect-fluid prediction at the same $G_{\\rm cosmo}/G_N$; disagreement beyond cosmic variance would mean the $\\Omega_g$ constraint is an artifact of the fluid description.","If the glitch is real, its signature should also appear in CMB lensing and in the large-angle kinetic Sunyaev-Zeldovich effect, the secondary temperature distortion from ionized gas, providing independent checks of the integrated Sachs-Wolfe signal that carries the current constraint.","The logarithmic-running scenario suggests a concrete extension: measuring the primordial helium abundance across multiple low-metallicity systems at different redshifts would trace $\\Omega_g$ at several nucleosynthesis epochs, testing whether the scale dependence is logarithmic rather than a single offset.","A positive glitch would produce an enhanced rather than suppressed large-scale ISW signal, so a future high-precision measurement of the low-multipole CMB temperature spectrum that finds an excess would falsify the preferred sign of the model."],"forward_implications":["A superhorizon gravity about one percent weaker than general relativity moves the Planck-inferred Hubble constant from $4.1\\sigma$ to $3.0\\sigma$ away from the local distance-ladder value, and Planck plus Dark Energy Survey data fit within $2.4\\sigma$.","The measured $S_8$-$\\Omega_m$ contours from DES and Planck overlap more under the glitch model, reducing the clustering tension in that parameter plane.","Including BAO data, DESI Y1 among them, tightens the glitch to $\\Omega_g = -0.0067 \\pm 0.0029$ with Planck PR4, showing the preference survives newer large-scale structure data.","If the glitch runs logarithmically with scale, the BBN constraint $\\Omega_g = -0.085 \\pm 0.027$ together with the CMB constraint implies near-vanishing Lorentz violation at the de Sitter radius and order-one violation near the Planck scale.","Stage-IV CMB and Euclid-like BAO surveys are forecast to shrink the uncertainty on $\\Omega_g$ below $10^{-3}$, enough to test whether the glitch is real or a statistical fluctuation."],"supporting_citations":[{"why":"Supplies the original cosmic glitch model and its CMB predictions, which this work reviews and extends with DESI Y1 and combined datasets.","marker":"[1]"},{"why":"Provides the Hořava–Lifshitz gravity theory as a concrete realization of the glitch.","marker":"[5]"},{"why":"Cuscuton gravity, another Lorentz-violating realization whose low-energy limit yields the effective Friedmann equation used here.","marker":"[6]"},{"why":"Einstein-Aether theory provides the third explicit gravity theory the glitch parameter can represent.","marker":"[7]"},{"why":"The CAMB Boltzmann code that is modified to compute CMB power spectra under the glitch model.","marker":"[12]"},{"why":"Introduces the parameterized post-Friedmann (PPF) framework used for the glitch's perturbation equations.","marker":"[13]"},{"why":"Provides the PPF implementation with rest-frame sound speed $c_s^2=1$ used for the numerical perturbation evolution.","marker":"[14]"},{"why":"The Planck 2018 likelihoods whose temperature, polarization, and lensing measurements carry the main $\\Omega_g$ constraint.","marker":"[15]"},{"why":"Derives the BBN glitch constraint $\\Omega_g=-0.085\\pm 0.027$ from helium abundance, enabling the running-glitch comparison.","marker":"[21]"},{"why":"DESI Y1 BAO data used in the combined CMB+BAO constraints.","marker":"[32]"}],"fun_headline_variants":["Cosmic data favor weaker gravity beyond the Hubble horizon","Gravity's 'cosmic glitch' may ease Hubble and clustering tensions","Planck and DESY1 hint gravity is ~1% weaker on largest scales","Weaker superhorizon gravity eases cosmic tensions in new fit","A single parameter set could fix cosmology's gravity mismatch"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The result stands on the assumption that a single smooth fluid with sound speed essentially that of light faithfully reproduces how real Lorentz-violating gravity theories perturb the CMB on superhorizon scales, so that the fitted $\\Omega_g$ actually measures $G_{\\rm cosmo}/G_N$.","fun_headline_variants_meta":{"raw":{"variants":["Cosmic data favor weaker gravity beyond the Hubble horizon","Gravity's 'cosmic glitch' may ease Hubble and clustering tensions","Planck and DESY1 hint gravity is ~1% weaker on largest scales","Weaker superhorizon gravity eases cosmic tensions in new fit","A single parameter set could fix cosmology's gravity mismatch"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000608,"raw_usage":{"total_tokens":2826,"prompt_tokens":933,"completion_tokens":1893,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":549,"completion_tokens_details":{"reasoning_tokens":1803}},"tokens_in":549,"tokens_out":1893,"duration_ms":27801,"temperature":1.0,"reasoning_tokens":1803,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T16:55:33.096626+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Compute the CMB temperature power spectrum at $\\ell < 100$ directly from an explicit Einstein-Aether or cuscuton action at fixed $G_{\\rm cosmo}/G_N$; if the predicted integrated Sachs-Wolfe signal differs from the PPF perfect-fluid prediction by more than cosmic variance, the fitted $\\Omega_g$ is an artifact of the effective parametrization. A cosmic-variance-limited measurement of $\\Omega_g$ consistent with zero at $\\sigma < 10^{-3}$ would likewise remove the current preference.","supporting_citations":[{"cited_title":"Ho ˇrava, Physical Review D79(8), 084008 (2009)","cited_arxiv_id":null,"evidence_quote":"Provides the Hořava–Lifshitz gravity theory as a concrete realization of the glitch."},{"cited_title":"Afshordi, Phys","cited_arxiv_id":null,"evidence_quote":"Cuscuton gravity, another Lorentz-violating realization whose low-energy limit yields the effective Friedmann equation used here."},{"cited_title":"Jacobson, Physical Review D 81(10), 101502 (2010)","cited_arxiv_id":null,"evidence_quote":"Einstein-Aether theory provides the third explicit gravity theory the glitch parameter can represent."},{"cited_title":"Hu, Phys","cited_arxiv_id":null,"evidence_quote":"Introduces the parameterized post-Friedmann (PPF) framework used for the glitch's perturbation equations."},{"cited_title":"Kohri, K.i","cited_arxiv_id":null,"evidence_quote":"Derives the BBN glitch constraint $\\Omega_g=-0.085\\pm 0.027$ from helium abundance, enabling the running-glitch comparison."}],"review_version":1}