{"id":"18d15dcd-4029-4dc3-8265-f745b91d7ff3","arxiv_id":"1908.07892","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":1.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"A review of parametrized frameworks (PPF, EFT, PPN, ppE) for testing gravity across cosmological and astrophysical scales, with an outlook toward unification.","lead":"This paper is a review of mathematical frameworks used to test modified gravity, covering cosmology, weak-field tests, and gravitational waves. It is a useful map for researchers choosing a parametrization for gravity tests, not a new scientific result.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No significant objection identified: the superhorizon limitation of the closure relations is explicitly disclosed in Sec. 2.2.2, so the review's descriptive central claim stands.","rationale":"The reader's weakest assumption correctly identifies the all-scale closure relations as the most delicate technical premise. I part ways only on the weight given to it: the manuscript itself flags the superhorizon caveat and points to the alternative formulation, so the premise is not silently load-bearing. The central claim is descriptive: the paper reviews existing parametrization frameworks and their connections. For that claim, the relevant risks are factual misattribution, omission of major frameworks, or internally inconsistent derivations, and I do not find compelling evidence of any. The paper repeatedly discloses limitations: quasistatic mu and gamma require care beyond Horndeski, PPNC lacks a relativistic completion, time-dependent-only parametrizations miss chameleon models, and screening complicates PPN. These disclosures strengthen, rather than weaken, the accuracy of the map. The self-acceleration section draws on the author's prior papers, but it is clearly attributed and not essential to the survey's main purpose. A verification of the closure-relation counting is still worth running as a routine check, but I do not see a basis for changing the verdict.","tokens_in":33120,"tokens_out":6344,"duration_ms":68866,"concrete_test":"Recompute the linear scalar mode count in Sec. 2.2.2 for a representative Horndeski model using the exact equations, without the quasistatic approximation, and check whether time- and scale-dependent mu and gamma in Eqs. (8) and (9) reproduce the exact superhorizon evolution of Phi, Psi, and Delta_m; if an extra source term is required, the paper's own caveat is confirmed and the review remains accurate because it flagged the limitation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"After reading in good faith, I do not find a load-bearing flaw in the paper's central claim that it accurately maps the parametrization landscape for tests of gravity. The most delicate technical premise is the all-scale use of the closure relations in Eqs. (8) and (9). If those relations silently failed on superhorizon scales, the PPF discussion would mislead. However, Sec. 2.2.2 explicitly states that mu and gamma generally take a simple analytic form only in the subhorizon limit, that superhorizon evolution is more naturally described by an extra summand in the Poisson equation, and that Eqs. (8) and (9) are adopted for all scales as a deliberate presentational choice, with Eq. (14) supplied for mapping models onto the effective fluid. Because this is a review whose claim is to survey and connect existing formalisms, a disclosed scope limitation of this kind does not falsify the map. The related assumption of matter conservation in Eqs. (10) and (11) is also stated rather than smuggled in; extensions to dark-sector interactions are referenced to the EFT literature. The self-acceleration discussion relies on prior work, but it is presented as such and is not needed for the survey claim.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper is a review of parametrized frameworks for testing gravity, covering the parametrized post-Friedmannian (PPF) frameworks for background, linear, and nonlinear cosmological scales, effective field theory approaches, gravitational wave propagation parametrizations, the parametrized post-Newtonian (PPN) formalism with screening extensions, the parametrized post-Einsteinian (ppE) and inspiral-merger-ringdown waveform models, and further approaches such as PPNC. It highlights connections between formalisms where they exist and provides an outlook toward a unified framework for tests of gravity and dark sector models.","tokens_in":33344,"tokens_out":6294,"duration_ms":61020,"significance":"If the descriptive claims hold, the review is a valuable map of a broad and technical field: it surveys many formalisms under a consistent notation, connects linear EFT functions to gravitational wave propagation and to nonlinear screening parametrizations, and explicitly discloses limitations such as the subhorizon validity of the closure relations in Sec. 2.2.2. The paper's strengths are its breadth, its consistent notation, and its careful attribution of results to the literature. The main weakness is a high density of self-citations for central relations, which is typical for a review by an active contributor and does not undermine the descriptive claim; the disclosed superhorizon limitation of Eqs. (8) and (9) is a stated scope restriction rather than a hidden flaw.","major_comments":[],"minor_comments":[{"comment":"The keywords are placeholders (\"Keyword1; keyword2; keyword3\") and the PACS numbers are missing; these should be filled before publication.","section":"Title page"},{"comment":"The definition \"h_ij ≡ g_ij/g_ii\" is not meaningful as written; h_ij should be defined as the spatial metric perturbation in the decomposition g_ij = a^2(δ_ij + h_ij) or an equivalent standard form, and the ratio g_ij/g_ii should be removed.","section":"Sec. 2.2.4, Eq. (23)"},{"comment":"The notation M_2^4 in the action and M^2 for the effective Planck mass is easy to confuse; a short table of EFT coefficients and their physical meanings would improve readability.","section":"Sec. 2.2.3"},{"comment":"The definitions of the new potentials and of β_BD and β_Scr in Eqs. (66)-(68) are not given in the text; a reader must consult Ref. 12, which is acceptable for a review but could be stated more explicitly.","section":"Sec. 3.3, Eqs. (62)-(68)"},{"comment":"The symbol γ is reused for the gravitational slip in Sec. 2.2.2, the PPN parameter in Sec. 3.2, and one of the PPNC functions in Sec. 4; although the text notes the analogy, a notation table or an explicit reminder of the different meanings would help.","section":"Sec. 4"},{"comment":"Reference entries are inconsistent: some are arXiv preprints without journal information (e.g., Refs. 110, 111, 119, 166), and several are labeled \"ArXiv e-prints\" even for works that have appeared in journals; the list should be updated.","section":"References"}],"recommendation":"minor_revision","confidential_remarks":"This is a single-author review with a substantial number of self-citations (Refs. 12, 41, 54, 58, 73, 82, 102 among others) for central results. I do not see this as a fairness problem, since the author is one of the main contributors to the formalism being reviewed, but the editor may wish to confirm that the self-citation density is appropriate for the journal. The manuscript fits the journal's scope."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper is a review, and it does not pretend otherwise. What it offers is a systematic map of the frameworks used to parametrize modified gravity across scales: PPF, EFT, PPN, ppE, and the screening parametrizations. As a map it is genuinely useful. The author knows the terrain firsthand, and the connections he draws between formalisms are the main value. The review also does something right that many reviews get wrong: it discloses where its working assumptions are limited. Section 2.2.2 explicitly says the closure relations (8) and (9) are adopted for all scales as a presentational choice, and that superhorizon evolution is better described by an extra summand. Similarly, the matter-conservation assumption behind Eqs. (10)-(11) is stated, not smuggled in. That is honest scholarship.\n\nThe soft spots are real but not disqualifying. The review leans heavily on the author's own prior work for key results: the self-acceleration conditions, the degeneracy relations, the screening parametrization, and the minimal-modification scenario all trace back to Lombriser and collaborators. The equations are presented as established without independent derivation in the text. For a review by a leading expert that is acceptable, but it means the survey is not impartial. A reader new to the field should know that the \"minimal modification\" story and the claimed 5-sigma tension in Standard Sirens carry the weight of prior analyses that are not fully reproduced here. The paper is also a conventional narrative review: no code, no data, no machine-checked proofs. That is fine for the genre.\n\nThe stress-test note is right: I read the superhorizon concern against the text, and the disclosure in Sec. 2.2.2 defuses it. The central claim of the paper, that these frameworks exist and can be connected, holds up. I would classify the novelty as low by design, and the significance as moderate: it will be a useful reference for practitioners and a convenient entry point for students, but it advances no new physics.\n\nWho is this for? Someone starting in modified gravity who wants a guided tour of the parametrization zoo, or an experienced researcher checking where a particular connection was made. It deserves a serious referee: a review of this scope by an active expert will be cited, and the refereeing should focus on the accuracy of attributions and the strength of the self-acceleration claims. I would recommend acceptance after minor revisions, mainly asking the author to flag more prominently where he is presenting his own prior conclusions rather than textbook consensus.","headline":"A competent, self-centric review of gravity parametrizations that is honest about its scope limits; worth refereeing as a reference article, not a source of new physics.","tokens_in":33809,"tokens_out":1364,"would_cite":true,"duration_ms":15895,"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":"This review shows that the major parametrization frameworks for testing gravity—PPN, PPF, EFT, and waveform models—form a connected map and can be unified through scalar-tensor theories with screening.","keywords":["parametrized post-Friedmannian formalism","effective field theory of dark energy","parametrized post-Newtonian formalism","parametrized post-Einsteinian formalism","modified gravity","cosmological perturbations","gravitational waves","screening mechanisms"],"falsifier":"Take a specific modified-gravity theory whose superhorizon behavior is known exactly and check whether its scalar perturbations can be reproduced by the two closure relations with some choice of $\\mu(a,k)$ and $\\gamma(a,k)$; a mismatch would falsify the claimed generality. A more direct test would be a measurement of the gravitational-wave speed at high redshift ($z \\gtrsim 1$) via a standard siren with an electromagnetic counterpart, which would probe whether the $c_T \\simeq 1$ assumption used to break the dark degeneracy holds where it matters for cosmic acceleration.","tokens_in":32908,"feed_emoji":"🌌","tokens_out":6457,"duration_ms":58572,"temperature":0.7,"pith_summary":"This review paper sets out to show that the many frameworks built to test gravity with cosmological, solar-system, and gravitational-wave observations are not isolated tools but connected pieces of a single underlying description. It surveys the parametrized post-Friedmannian (PPF) formalism, the effective field theory (EFT) of dark energy, the parametrized post-Newtonian (PPN) expansion, and parametrized gravitational-wave formalisms, and it collects the known translation rules between them. The payoff of the map is practical: a measurement made in one regime, such as the speed of gravitational waves, can be used to constrain or exclude modifications of gravity that would otherwise hide in the large-scale structure. The paper argues that a global parametrization covering all scales is feasible, with scalar-tensor theories and their screening mechanisms as the natural bridge.","feed_headline":"One map connects gravity tests from solar system to GWs","feed_subtitle":"A review shows PPN, PPF, EFT, and waveform parameterizations are linked and unifiable through scalar-tensor theories.","key_machinery":"The load-bearing object is the pair of closure relations for linear perturbations—the modified Poisson equation and the gravitational slip, $\\mu(a,k)$ and $\\gamma(a,k)$—together with the effective gravitational coupling $G_{\\rm eff}$ whose radial profile is parametrized by a modular transition function between screened and unscreened regimes. These encode the gravitational modification in a way that can be mapped onto the EFT functions ($\\alpha_K$, $\\alpha_B$, $\\alpha_M$, $\\alpha_T$) and onto the gravitational-wave propagation parameters ($\\nu$, $c_T$, $\\tilde{\\mu}$, $\\Gamma$). The work these objects do is to turn a theory space into a small set of measurable functions of time and scale, so that the same measurement, like the nearly equal speeds of light and gravitational waves from GW170817, can be propagated through the network of formalisms and applied to all regimes.","core_discovery":"The central claim is that the apparent diversity of parametrization schemes for tests of gravity reduces to a small set of shared physical building blocks. At the level of linear cosmological perturbations, the entire space of metric modified-gravity models is encoded in two closure relations: a modified Poisson equation, $k_H^2 \\Psi = -\\frac{\\kappa^2 \\bar{\\rho}_m}{2H^2} \\mu(a,k) \\Delta_m$, and a gravitational slip, $\\Phi = -\\gamma(a,k) \\Psi$, which take simple analytic forms in the subhorizon limit and can be mapped to the coefficients of the effective field theory. The same building blocks reappear in the gravitational-wave sector: the running Planck mass $\\nu$ and the speed $c_T$ enter both the propagation equation for the wave and the condition for genuine cosmic self-acceleration. On static weak-field scales, the PPN parameters (notably $\\gamma$ and $\\beta$) are the analogues of the slip, and the paper shows how screening mechanisms can be incorporated either by promoting PPN parameters to functions of position or by adding new potentials. The paper's constructive proposal is that a unified framework can be built by reconstructing the Lagrangian of the scalar-tensor theory from a few time-dependent functions, such as the scalar mass and coupling at the minimum of its effective potential, which then connects all regimes.","pith_inferences":["One could test the superhorizon generality of the $\\mu$–$\\gamma$ closure by comparing its predictions against a theory with explicitly known superhorizon evolution, such as a nonlocal or higher-derivative model, to see whether the closure misses observables.","The modular transition function for $G_{\\rm eff}$ suggests a direct route to parametrizing screened gravitational-wave emission at the source, which the paper notes remains an open problem; a waveform-level analogue of the transition function is a plausible extension.","Because the paper notes that early-time modifications are often dropped by assumption, a natural extension is to include early-time $\\mu$ and $\\gamma$ in forecasts for future surveys; current constraints may be artificially optimistic."],"forward_implications":["If the closure relations hold at all scales, a single pair of functions $\\mu(a,k)$ and $\\gamma(a,k)$ suffices to compute linear modified-gravity predictions from superhorizon to subhorizon scales, including the integrated Sachs-Wolfe effect and lensing.","The GW170817 bound $c_T \\simeq 1$ implies that genuine cosmic self-acceleration in Horndeski gravity must be driven by an evolving effective Planck mass, and the minimal such scenario is disfavored at about $3\\sigma$ by current cosmological data.","Percent-level Standard Siren measurements of the luminosity distance can turn the minimal scalar-tensor self-acceleration scenario into a conclusive $5\\sigma$ test.","A unified parametrization for chameleon, dilaton, and symmetron models can be reconstructed from the cosmological time variation of the scalar mass and coupling at the minimum of the effective potential, connecting laboratory, solar-system, and cosmological tests."],"supporting_citations":[{"why":"Defines the parametrized post-Newtonian expansion, the low-energy static weak-field formalism that the paper contrasts with cosmological frameworks.","marker":"8, 9"},{"why":"Introduces the parametrized post-Friedmannian closure relations (modified Poisson equation and gravitational slip) for linear cosmological perturbations.","marker":"13–17"},{"why":"Establishes the effective field theory of dark energy and modified gravity, whose coefficients are mapped to the PPF functions.","marker":"22–30"},{"why":"Introduces the parametrized post-Einsteinian framework for gravitational waveforms, connected to propagation effects in Sec. 2.2.4.","marker":"47"},{"why":"Derives the relation between the gravitational-wave speed, the effective Planck mass evolution, and genuine cosmic self-acceleration, used throughout the review to break degeneracies.","marker":"54"},{"why":"Provides the modular parametrization of $G_{\\rm eff}$ with screening transitions that the review uses for nonlinear structure formation.","marker":"41"},{"why":"Gives the unified chameleon/dilaton/symmetron parametrization through the scalar mass and coupling, the basis for the proposed global unification.","marker":"32"}],"fun_headline_variants":["One gravity map spans PPN, PPF, and waveforms","Gravity tests converge to a single parametrization","Unified blueprint for gravity probes at every scale","From solar system to gravitational waves: one theory","How all gravity tests share one skeleton"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole map assumes that two closure relations—a modified Poisson equation and a gravitational slip—can faithfully describe the linear perturbations of every relevant metric theory of modified gravity at every scale, including superhorizon scales, because the review adopts them for all scales.","fun_headline_variants_meta":{"raw":{"variants":["One gravity map spans PPN, PPF, and waveforms","Gravity tests converge to a single parametrization","Unified blueprint for gravity probes at every scale","From solar system to gravitational waves: one theory","How all gravity tests share one skeleton"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000488,"raw_usage":{"total_tokens":2427,"prompt_tokens":994,"completion_tokens":1433,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":610,"completion_tokens_details":{"reasoning_tokens":1360}},"tokens_in":610,"tokens_out":1433,"duration_ms":11536,"temperature":1.0,"reasoning_tokens":1360,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T11:53:14.699527+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Take a specific modified-gravity theory whose superhorizon behavior is known exactly and check whether its scalar perturbations can be reproduced by the two closure relations with some choice of $\\mu(a,k)$ and $\\gamma(a,k)$; a mismatch would falsify the claimed generality. A more direct test would be a measurement of the gravitational-wave speed at high redshift ($z \\gtrsim 1$) via a standard siren with an electromagnetic counterpart, which would probe whether the $c_T \\simeq 1$ assumption used to break the dark degeneracy holds where it matters for cosmic acceleration.","supporting_citations":[],"review_version":1}