pith. sign in

arxiv: 2606.31274 · v1 · pith:VHWSP73Snew · submitted 2026-06-30 · 🌀 gr-qc · hep-th

Fragility of stealth solutions in mimetic gravity

Pith reviewed 2026-07-01 04:43 UTC · model grok-4.3

classification 🌀 gr-qc hep-th
keywords mimetic gravitystealth solutionsLagrange multiplierperturbative degeneracyscreening mechanismconstrained extensionsgeneral relativity
0
0 comments X

The pith

The lambda-bar to zero limit in mimetic gravity is generically non-uniform, rendering stealth solutions perturbatively pathological.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper studies constrained mimetic-type extensions of general relativity where a Lagrange multiplier enforces a scalar functional constraint C on the metric and other fields. On the stealth branch where the background value of the multiplier vanishes, the constrained sector drops out of the background equations, allowing any general relativity geometry to serve as a solution provided a background field profile satisfies the constraint. The same branch nevertheless remains perturbatively degenerate with general relativity because the constrained sector still enters the fluctuation equations only through terms multiplied by the background multiplier, while simultaneously imposing an infinite hierarchy of constraints on those fluctuations. A sympathetic reader would care because this non-uniformity means the simple screening-like behavior expected when the multiplier is small locally cannot be trusted at the level of linear perturbations around stealth solutions.

Core claim

On the exactly stealth branch where bar lambda equals zero, the constrained sector drops out of the background dynamics so that general relativity geometries are admitted as stealth solutions whenever a background profile satisfying bar C equals zero exists. At the general level the bar lambda equals zero branch is perturbatively degenerate with general relativity: the constrained sector contributes to the dynamics only through terms weighted by bar lambda, which vanish on the stealth branch, while still imposing an infinite hierarchy of constraints on the fluctuations. Consequently the bar lambda to zero limit is generically non-uniform, making the would-be screening perturbatively patholog

What carries the argument

The Lagrange multiplier lambda enforcing the constraint functional C[g, Psi] equals zero, which decouples from background dynamics on the stealth branch yet generates an infinite tower of constraints on linear fluctuations.

If this is right

  • Stealth solutions exist for any general relativity geometry on domains where a background profile satisfying the constraint can be found.
  • Perturbations around those solutions remain subject to an infinite set of constraints even though the multiplier background value is zero.
  • The screening-like decoupling of the constrained sector therefore cannot be treated as a uniform limit in perturbation theory.
  • Explicit constructions such as the stealth Kerr solution obtained via Carter separability inherit the same perturbative degeneracy.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The non-uniformity may require resummation or non-perturbative methods when modeling transitions from cosmological scales where bar lambda is nonzero to local regions where it is small.
  • Similar fragility could appear in other constrained modifications of gravity that rely on a multiplier to enforce a screening condition.
  • One testable extension would be to compute the dispersion relations of fluctuations in a specific scalar-field realization and check whether the infinite constraints produce ghosts or instabilities at finite but small bar lambda.

Load-bearing premise

The constrained sector contributes to dynamics only through terms weighted by bar lambda which vanish on the stealth branch while imposing an infinite hierarchy of constraints on fluctuations.

What would settle it

An explicit linear perturbation analysis around a concrete stealth solution such as the constructed stealth Kerr metric that demonstrates either the absence of the infinite constraint hierarchy or the recovery of a uniform limit as bar lambda approaches zero.

read the original abstract

We study a broad class of constrained mimetic-type extensions of general relativity with action $S=\int{\rm d}^4x\sqrt{-g}\,\bigl(R/2+\lambda\,C[g,\Psi]+{\cal L}_{\rm m}\bigr)$, where $R$ is the Ricci scalar, $\lambda$ is a Lagrange multiplier, $C[g,\Psi]$ is a scalar functional of the metric and generic field content $\Psi$ (possibly involving $\Psi$ and its covariant derivatives) and ${\cal L}_{\rm m}$ is the matter Lagrangian. The branch $\bar\lambda\to 0$, with the bar denoting a background value, provides a simple screening-like limit in which the constrained sector decouples, as in cosmological realizations where $\bar\lambda$ is typically nonzero on large scales while locally one expects $\bar\lambda\simeq 0$. On the exactly stealth branch $\bar{\lambda}=0$, the constrained sector drops out of the background dynamics, so, on domains where a background profile $\bar\Psi$ satisfying $\bar C=0$ exists, the theory admits the corresponding general relativity geometries as stealth solutions. As an explicit realization of this mechanism, we consider the scalar field case, where $C=g^{\mu\nu}\partial_\mu\phi\partial_\nu\phi\pm1=0$ becomes a Hamilton-Jacobi equation selecting geodesic congruences; in this setting, we study spherically symmetric solutions and construct a stealth Kerr profile using Carter separability. We then show, at the general level, that the $\bar{\lambda}=0$ branch is perturbatively degenerate with general relativity: the constrained sector contributes to the dynamics only through terms weighted by $\bar\lambda$, which vanish on the stealth branch, while still imposing an infinite hierarchy of constraints on the fluctuations. Consequently, the $\bar\lambda\to0$ limit is generically non-uniform, making the would-be screening perturbatively pathological.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript analyzes a broad class of constrained mimetic extensions of GR with action involving a Lagrange multiplier λ enforcing C[g,Ψ]=0. On the stealth branch where background λ-bar=0, the constrained sector decouples and GR geometries are admitted as solutions provided a background profile satisfying C-bar=0 exists. An explicit stealth Kerr solution is constructed via Carter separability for the scalar-field case C=g^{μν}∂_μφ∂_νφ±1=0. At the general level the authors argue that the λ-bar→0 limit is non-uniform: the constrained sector contributes to dynamics only through λ-weighted terms (vanishing on the stealth branch) while imposing an infinite hierarchy of constraints on fluctuations, rendering the screening perturbatively pathological.

Significance. If the central claim is substantiated, the result identifies a structural obstruction to perturbative recovery of GR in the screened limit for this class of models, with direct implications for the viability of mimetic screening mechanisms. The explicit construction of the stealth Kerr geometry via Carter separability and the general argument on perturbative degeneracy constitute concrete strengths; the absence of free parameters or ad-hoc entities in the core claim is also a positive feature.

major comments (1)
  1. [Abstract (perturbative degeneracy paragraph)] Abstract (perturbative degeneracy paragraph): the assertion that the constrained sector 'imposes an infinite hierarchy of constraints on the fluctuations' while contributing only through λ-weighted terms is presented at the general level without an explicit linearized fluctuation system, count of propagating degrees of freedom, or identification of a concrete object (quadratic action, dispersion relation, or constraint algebra) whose λ→0 limit fails to commute. This step is load-bearing for the non-uniformity claim.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of the explicit stealth Kerr construction and the general argument, as well as for identifying the load-bearing nature of the perturbative non-uniformity claim. We address the single major comment below.

read point-by-point responses
  1. Referee: Abstract (perturbative degeneracy paragraph): the assertion that the constrained sector 'imposes an infinite hierarchy of constraints on the fluctuations' while contributing only through λ-weighted terms is presented at the general level without an explicit linearized fluctuation system, count of propagating degrees of freedom, or identification of a concrete object (quadratic action, dispersion relation, or constraint algebra) whose λ→0 limit fails to commute. This step is load-bearing for the non-uniformity claim.

    Authors: The general argument rests on the structure of the action S = ∫ d⁴x √-g (R/2 + λ C[g,Ψ] + ℒ_m). On a stealth background with ar λ = 0 the term λ C contributes nothing to the background equations and, upon expansion to quadratic order in fluctuations, supplies no dynamical quadratic terms because it is multiplied by ar λ. The constraint C[g,Ψ] = 0 must nevertheless hold identically on the full solution; expanding C order by order therefore generates an infinite tower of conditions on the perturbation fields (one at each perturbative order). This is the source of the non-uniformity: the dynamical contributions vanish with ar λ while the constraints survive. Because the reasoning follows directly from the multiplicative placement of λ and the requirement that C vanish everywhere, it applies to the entire class without needing a model-specific quadratic action. We will, however, add a short explicit linearization for the scalar-field case (C = g^{μν}∂_μφ∂_νφ ± 1) in a revised manuscript to make the hierarchy concrete and to exhibit the vanishing of the quadratic action term. revision: yes

Circularity Check

0 steps flagged

No circularity: claim follows directly from action structure without reduction to inputs

full rationale

The derivation begins from the explicit action S = ∫ d⁴x √-g (R/2 + λ C[g,Ψ] + L_m) and defines the stealth branch by setting barλ = 0, which by construction drops the constrained sector from background equations while the multiplier still enforces C=0. The statement that fluctuations receive only barλ-weighted contributions (hence non-uniform limit) is a direct consequence of varying this action; no parameter is fitted and then relabeled as prediction, no self-citation supplies a uniqueness theorem, and no ansatz is smuggled. The infinite-constraint hierarchy is asserted at the general level from the multiplier formalism itself rather than derived via explicit linearization in the provided text, but this is an incompleteness of exposition, not a circular reduction. The Kerr construction via Carter separability is independent and does not feed back into the degeneracy claim.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Paper assumes standard constrained mimetic action form; no free parameters, new entities or ad-hoc axioms beyond domain assumptions of GR extensions. Abstract-only so full details unavailable.

axioms (1)
  • domain assumption Action takes form S=∫d⁴x√-g (R/2 + λ C[g,Ψ] + L_m) with C a scalar functional.
    Invoked at start of abstract as the broad class under study.

pith-pipeline@v0.9.1-grok · 18223 in / 1071 out tokens · 143172 ms · 2026-07-01T04:43:44.185469+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

57 extracted references · 54 canonical work pages · 35 internal anchors

  1. [1]

    Cosmological Tests of Gravity

    B. Jain and J. Khoury,Cosmological Tests of Gravity, Annals Phys.325(2010) 1479 [arXiv:1004.3294]

  2. [2]

    Brax,Screening mechanisms in modified gravity, Class

    P. Brax,Screening mechanisms in modified gravity, Class. Quant. Grav.30(2013) 214005

  3. [3]

    Beyond the Cosmological Standard Model

    A. Joyce, B. Jain, J. Khoury and M. Trodden,Beyond the Cosmological Standard Model, Phys. Rept.568(2015) 1 [arXiv:1407.0059]

  4. [4]

    Cosmological Tests of Modified Gravity

    K. Koyama,Cosmological Tests of Modified Gravity, Rept. Prog. Phys.79(2016) 046902 [arXiv:1504.04623]

  5. [5]

    Dark Energy vs. Modified Gravity

    A. Joyce, L. Lombriser and F. Schmidt,Dark Energy Versus Modified Gravity, Ann. Rev. Nucl. Part. Sci.66(2016) 95 [arXiv:1601.06133]

  6. [6]

    Tests of Chameleon Gravity

    C. Burrage and J. Sakstein,Tests of Chameleon Gravity, Living Rev. Rel.21(2018) 1 [arXiv:1709.09071]

  7. [7]

    Vainshtein mechanism after GW170817

    M. Crisostomi and K. Koyama,Vainshtein mechanism after GW170817, Phys. Rev. D 97(2018) 021301 [arXiv:1711.06661]. 15

  8. [8]

    Elliptic problems on complete non-compact Riemannian manifolds with asymptotically non-negative Ricci curvature

    T. Kobayashi, Y. Watanabe and D. Yamauchi,Vainshtein screening in scalar-tensor theories before and after gw170817: Constraints on theories beyond horndeski, Physical Review D98(2018) 064035 [arXiv:1803.07494]

  9. [9]

    Ishak, Living Rev

    M. Ishak,Testing General Relativity in Cosmology, Living Rev. Rel.22(2019) 1 [arXiv:1806.10122]

  10. [10]

    Amendola, D

    L. Amendola, D. Bettoni, A. M. Pinho and S. Casas,Measuring gravity at cosmological scales, Universe6(2020) 20 [arXiv:1902.06978]

  11. [11]

    Horndeski theory and beyond: a review

    T. Kobayashi,Horndeski theory and beyond: a review, Rept. Prog. Phys.82(2019) 086901 [arXiv:1901.07183]

  12. [12]

    P. G. Ferreira,Cosmological Tests of Gravity, Ann. Rev. Astron. Astrophys.57(2019) 335 [arXiv:1902.10503]

  13. [13]

    Sakstein,Astrophysical tests of screened modified gravity, Int

    J. Sakstein,Astrophysical tests of screened modified gravity, Int. J. Mod. Phys. D27 (2018) 1848008 [arXiv:2002.04194]

  14. [14]

    P. Brax, S. Casas, H. Desmond and B. Elder,Testing Screened Modified Gravity, Universe8(2021) 11 [arXiv:2201.10817]

  15. [15]

    Vainshtein screening in a cosmological background in the most general second-order scalar-tensor theory

    R. Kimura, T. Kobayashi and K. Yamamoto,Vainshtein screening in a cosmological background in the most general second-order scalar-tensor theory, Phys. Rev. D85 (2012) 024023 [arXiv:1111.6749]

  16. [16]

    A. H. Chamseddine and V. Mukhanov,Mimetic Dark Matter, JHEP11(2013) 135 [arXiv:1308.5410]

  17. [17]

    Disformal Transformations, Veiled General Relativity and Mimetic Gravity

    N. Deruelle and J. Rua,Disformal Transformations, Veiled General Relativity and Mimetic Gravity, JCAP09(2014) 002 [arXiv:1407.0825]

  18. [18]

    The two faces of mimetic Horndeski gravity: disformal transformations and Lagrange multiplier

    F. Arroja, N. Bartolo, P. Karmakar and S. Matarrese,The two faces of mimetic Horndeski gravity: disformal transformations and Lagrange multiplier, JCAP09(2015) 051 [arXiv:1506.08575]

  19. [19]

    On the recently proposed Mimetic Dark Matter

    A. Golovnev,On the recently proposed Mimetic Dark Matter, Phys. Lett. B728(2014) 39 [arXiv:1310.2790]

  20. [20]

    A. O. Barvinsky,Dark matter as a ghost free conformal extension of Einstein theory, JCAP01(2014) 014 [arXiv:1311.3111]

  21. [21]

    A. H. Chamseddine, V. Mukhanov and A. Vikman,Cosmology with Mimetic Matter, JCAP06(2014) 017 [arXiv:1403.3961]

  22. [22]

    Mimetic dark matter, ghost instability and a mimetic tensor-vector-scalar gravity

    M. Chaichian, J. Kluson, M. Oksanen and A. Tureanu,Mimetic dark matter, ghost instability and a mimetic tensor-vector-scalar gravity, JHEP12(2014) 102 [arXiv:1404.4008]. 16

  23. [23]

    Imperfect Dark Matter

    L. Mirzagholi and A. Vikman,Imperfect Dark Matter, JCAP06(2015) 028 [arXiv:1412.7136]

  24. [24]

    Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations

    J. Ben Achour, D. Langlois and K. Noui,Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations, Phys. Rev. D93(2016) 124005 [arXiv:1602.08398]

  25. [25]

    Mimetic gravity: a review of recent developments and applications to cosmology and astrophysics

    L. Sebastiani, S. Vagnozzi and R. Myrzakulov,Mimetic gravity: a review of recent developments and applications to cosmology and astrophysics, Adv. High Energy Phys. 2017(2017) 3156915 [arXiv:1612.08661]

  26. [26]

    Instabilities in Mimetic Matter Perturbations

    H. Firouzjahi, M. A. Gorji and S. A. Hosseini Mansoori,Instabilities in Mimetic Matter Perturbations, JCAP07(2017) 031 [arXiv:1703.02923]

  27. [27]

    On (in)stabilities of perturbations in mimetic models with higher derivatives

    Y. Zheng, L. Shen, Y. Mou and M. Li,On (in)stabilities of perturbations in mimetic models with higher derivatives, JCAP08(2017) 040 [arXiv:1704.06834]

  28. [28]

    Extended mimetic gravity: Hamiltonian analysis and gradient instabilities

    K. Takahashi and T. Kobayashi,Extended mimetic gravity: Hamiltonian analysis and gradient instabilities, JCAP11(2017) 038 [arXiv:1708.02951]

  29. [29]

    Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations

    S. Hirano, S. Nishi and T. Kobayashi,Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations, JCAP07(2017) 009 [arXiv:1704.06031]

  30. [30]

    M. A. Gorji, S. A. Hosseini Mansoori and H. Firouzjahi,Higher Derivative Mimetic Gravity, JCAP01(2018) 020 [arXiv:1709.09988]

  31. [31]

    Mimetic gravity as DHOST theories

    D. Langlois, M. Mancarella, K. Noui and F. Vernizzi,Mimetic gravity as DHOST theories, JCAP02(2019) 036 [arXiv:1802.03394]

  32. [32]

    Two-field disformal transformation and mimetic cosmology

    H. Firouzjahi, M. A. Gorji, S. A. Hosseini Mansoori, A. Karami and T. Rostami, Two-field disformal transformation and mimetic cosmology, JCAP11(2018) 046 [arXiv:1806.11472]

  33. [33]

    M. A. Gorji, S. Mukohyama, H. Firouzjahi and S. A. Hosseini Mansoori,Gauge Field Mimetic Cosmology, JCAP08(2018) 047 [arXiv:1807.06335]

  34. [34]

    New Weyl-invariant vector-tensor theory for the cosmological constant

    P. Jiroušek and A. Vikman,New Weyl-invariant vector-tensor theory for the cosmological constant, JCAP04(2019) 004 [arXiv:1811.09547]

  35. [35]

    M. A. Gorji, S. Mukohyama and H. Firouzjahi,Cosmology in Mimetic SU(2) Gauge Theory, JCAP05(2019) 019 [arXiv:1903.04845]

  36. [36]

    A. Ganz, N. Bartolo and S. Matarrese,Towards a viable effective field theory of mimetic gravity, JCAP12(2019) 037 [arXiv:1907.10301]

  37. [37]

    M. A. Gorji, A. Allahyari, M. Khodadi and H. Firouzjahi,Mimetic black holes, Phys. Rev. D101(2020) 124060 [arXiv:1912.04636]

  38. [38]

    S. A. H. Mansoori, A. Talebian, Z. Molaee and H. Firouzjahi,Multifield mimetic gravity, Phys. Rev. D105(2022) 023529 [arXiv:2108.11666]. 17

  39. [39]

    Jiroušek, K

    P. Jiroušek, K. Shimada, A. Vikman and M. Yamaguchi,Disforming to conformal symmetry, JCAP11(2022) 019 [arXiv:2207.12611]

  40. [40]

    Zheng and H

    Y. Zheng and H. Rao,Extensions of two-field mimetic gravity, JHEP04(2023) 042 [arXiv:2210.10499]

  41. [41]

    Jiroušek, K

    P. Jiroušek, K. Shimada, A. Vikman and M. Yamaguchi,Mimetic K-essence, arXiv:2212.14867

  42. [42]

    Domènech and A

    G. Domènech and A. Ganz,Disformal symmetry in the Universe: mimetic gravity and beyond, JCAP08(2023) 046 [arXiv:2304.11035]

  43. [43]

    D.-I. Visa, T. Harko and S. Shahidi,Mimetic Weyl geometric gravity, Phys. Dark Univ. 46(2024) 101720 [arXiv:2410.22787]

  44. [44]

    Colléaux and K

    A. Colléaux and K. Noui,Degenerate higher-order Maxwell-Einstein theories, JHEP10 (2025) 007 [arXiv:2502.03311]

  45. [45]

    M. A. Gorji,Imperfect dark matter with higher derivatives,arXiv:2510.23838

  46. [46]

    M. A. Gorji, S. Jana and P. Petrov,Abelian and non-Abelian mimetic black holes, arXiv:2511.22062

  47. [47]

    Gravity with a dynamical preferred frame

    T. Jacobson and D. Mattingly,Gravity with a dynamical preferred frame, Phys. Rev. D 64(2001) 024028 [arXiv:gr-qc/0007031]

  48. [48]

    D. Blas, O. Pujolas and S. Sibiryakov,On the Extra Mode and Inconsistency of Horava Gravity, JHEP10(2009) 029 [arXiv:0906.3046]

  49. [49]

    Hammer, P

    K. Hammer, P. Jirousek and A. Vikman,Axionic cosmological constant, arXiv:2001.03169

  50. [50]

    Charmousis, M

    C. Charmousis, M. Crisostomi, R. Gregory and N. Stergioulas,Rotating Black Holes in Higher Order Gravity, Phys. Rev. D100(2019) 084020 [arXiv:1903.05519]

  51. [51]

    Takahashi and H

    K. Takahashi and H. Motohashi,General Relativity solutions with stealth scalar hair in quadratic higher-order scalar-tensor theories, JCAP06(2020) 034 [arXiv:2004.03883]

  52. [52]

    Ben Achour, H

    J. Ben Achour, H. Liu, H. Motohashi, S. Mukohyama and K. Noui,On rotating black holes in DHOST theories, JCAP11(2020) 001 [arXiv:2006.07245]

  53. [53]

    Chandrasekhar,The Mathematical Theory of Black Holes

    S. Chandrasekhar,The Mathematical Theory of Black Holes. Oxford University Press, New York, 1983

  54. [54]

    C. W. Misner, K. S. Thorne and J. A. Wheeler,Gravitation. W. H. Freeman, San Francisco, 1973

  55. [55]

    Charged particle motion in Kerr-Newmann space-times

    E. Hackmann and H. Xu,Charged particle motion in kerr-newman space-times, Physical Review D87(2013) 124030 [arXiv:1304.2142]. 18

  56. [56]

    Observation of Gravitational Waves from a Binary Black Hole Merger

    B. Carter,Global structure of the kerr family of gravitational fields, Physical Review 174(1968) 1559. [57]LIGO Scientific, Virgocollaboration, B. P. Abbott et al.,Observation of Gravitational Waves from a Binary Black Hole Merger, Phys. Rev. Lett.116(2016) 061102 [arXiv:1602.03837]

  57. [57]

    LIGO Scientific, Virgocollaboration, B. P. Abbott et al.,Tests of general relativity with GW150914, Phys. Rev. Lett.116(2016) 221101 [arXiv:1602.03841]. [59]LIGO Scientific, Virgocollaboration, R. Abbott et al.,Tests of general relativity with binary black holes from the second LIGO-Virgo gravitational-wave transient catalog, Phys. Rev. D103(2021) 122002 ...