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Galaxy morphology rules out astrophysically relevant Hu-Sawicki $f(R)$ gravity
Cosmology and Nongalactic Astrophysics · Submitted 18 Sep 2020
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We conclude that this model can have no relevance to astrophysics or cosmology.
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The abstract, sentence by sentence
$f(R)$ is a paradigmatic modified gravity theory that typifies extensions to General Relativity with new light degrees of freedom and hence screened fifth forces between masses. These forces produce observable signatures in galaxy morphology, caused by a violation of the weak equivalence principle due to a differential impact of screening among galaxies' mass components. We compile statistical datasets of two morphological indicators -- offsets between stars and gas in galaxies and warping of stellar disks -- and use them to constrain the strength and range of a thin-shell-screened fifth force. This is achieved by applying a comprehensive set of upgrades to past work (Desmond et al 2018a,b): we construct a robust galaxy-by-galaxy Bayesian forward model for the morphological signals, including full propagation of uncertainties in the input quantities and marginalisation over an empirical model describing astrophysical noise. Employing more stringent data quality cuts than previously we find no evidence for a screened fifth force of any strength $\Delta G/G_\text{N}$ in the Compton wavelength range $0.3-8$ Mpc, setting a $1\sigma$ bound of $\Delta G/G_\text{N}<0.8$ at $\lambda_C=0.3$ Mpc that strengthens to $\Delta G/G_\text{N}<3\times10^{-5}$ at $\lambda_C=8$ Mpc. These are the tightest bounds to date beyond the Solar System by over an order of magnitude. For the Hu-Sawicki model of $f(R)$ with $n=1$ we require a background scalar field value $f_{R0} < 1.4 \times 10^{-8}$, forcing practically all astrophysical objects to be screened. We conclude that this model can have no relevance to astrophysics or cosmology.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | $f(R)$ is a paradigmatic modified gravity theory that typifies extensions to General Relativity with new light degrees of freedom and hence screened fifth forces between masses. | background 1.00 | 0.04 | 0.01 | asserted 1.00 |
| s1 | These forces produce observable signatures in galaxy morphology, caused by a violation of the weak equivalence principle due to a differential impact of screening among galaxies' mass components. | background 0.99 | 0.08 | 0.02 | asserted 1.00 |
| s2 | We compile statistical datasets of two morphological indicators -- offsets between stars and gas in galaxies and warping of stellar disks -- and use them to constrain the strength and range of a thin-shell-screened fifth force. | method 0.65 | 0.96 | 0.02 | asserted 0.98 |
| s3 | This is achieved by applying a comprehensive set of upgrades to past work (Desmond et al 2018a,b): we construct a robust galaxy-by-galaxy Bayesian forward model for the morphological signals, including full propagation of uncertainties in the input quantities and marginalisation over an empirical model describing astrophysical noise. | method 0.94 | 0.94 | 0.02 | asserted 0.99 |
| s4 | Employing more stringent data quality cuts than previously we find no evidence for a screened fifth force of any strength $\Delta G/G_\text{N}$ in the Compton wavelength range $0.3-8$ Mpc, setting a $1\sigma$ bound of $\Delta G/G_\text{N}<0.8$ at $\lambda_C=0.3$ Mpc that strengthens to $\Delta G/G_\text{N}<3\times10^{-5}$ at $\lambda_C=8$ Mpc. | result 1.00 | 0.97 | 0.24 | asserted 1.00 |
| s5 | These are the tightest bounds to date beyond the Solar System by over an order of magnitude. | interpretation 0.66 | 0.86 | 0.07 | asserted 1.00 |
| s6 | For the Hu-Sawicki model of $f(R)$ with $n=1$ we require a background scalar field value $f_{R0} < 1.4 \times 10^{-8}$, forcing practically all astrophysical objects to be screened. | result 0.58 | 0.87 | 0.09 | asserted 1.00 |
| s7 | We conclude that this model can have no relevance to astrophysics or cosmology. | interpretation 0.99 | 0.59 | 0.94 | asserted 1.00 |
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The paper
Original abstract
$f(R)$ is a paradigmatic modified gravity theory that typifies extensions to General Relativity with new light degrees of freedom and hence screened fifth forces between masses. These forces produce observable signatures in galaxy morphology, caused by a violation of the weak equivalence principle due to a differential impact of screening among galaxies' mass components. We compile statistical datasets of two morphological indicators -- offsets between stars and gas in galaxies and warping of stellar disks -- and use them to constrain the strength and range of a thin-shell-screened fifth force. This is achieved by applying a comprehensive set of upgrades to past work (Desmond et al 2018a,b): we construct a robust galaxy-by-galaxy Bayesian forward model for the morphological signals, including full propagation of uncertainties in the input quantities and marginalisation over an empirical model describing astrophysical noise. Employing more stringent data quality cuts than previously we find no evidence for a screened fifth force of any strength $\Delta G/G_\text{N}$ in the Compton wavelength range $0.3-8$ Mpc, setting a $1\sigma$ bound of $\Delta G/G_\text{N}<0.8$ at $\lambda_C=0.3$ Mpc that strengthens to $\Delta G/G_\text{N}<3\times10^{-5}$ at $\lambda_C=8$ Mpc. These are the tightest bounds to date beyond the Solar System by over an order of magnitude. For the Hu-Sawicki model of $f(R)$ with $n=1$ we require a background scalar field value $f_{R0} < 1.4 \times 10^{-8}$, forcing practically all astrophysical objects to be screened. We conclude that this model can have no relevance to astrophysics or cosmology.
Human review
References
How the literature uses it
25 arXiv papers cite this in 33 sentences
Papers citing it · 23 sentences without a confident label
Uses its method or tool 2 papers
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Following [ref] , we model the samples as a Gaussian mixture model (GMM) [ref] where the likelihood function for some galaxy $g$ is [equation] where [equation] and ${ w^( i ), σ^( i ),μ^( i ) }$, the weights, standard deviations and means of the Gaussians, are implicit functions of $r_V$.
Constraints on galileons from the positions of supermassive black holes · Gaussian mixture model · 1.00
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The screening status of the host galaxy can then be determined using screening maps [ref] , which determine whether an individual galaxy is screened or not and provide the (environment-dependent) value of $ΔG/G_N$ as a function of the theory parameters.
Modified Gravity and the Black Hole Mass Gap · Observational Signatures and Detection Strategies · 0.92
Uses its data or values 2 papers
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The WEP in the dark sector can be tested by looking for the effects on the tidal disruption of Milky Way Satellites [ref] , yielding $β_DM<𝒪(0.1)$, and, recently, tests of the WEP between baryons and dark matter using the predicted warping of galaxies has constrained $β_DM^2-β_SM^2<5×10^-5$ [ref] .
Neutrino-Assisted Early Dark Energy: Theory and Cosmology · Couplings to Other Standard Model Particles and the Dark Sector · 0.89
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Current constraints from astrophysical scales give $|f_R0| ≲10^-8$ [ref] while a recent joint analysis of SPT clusters and Planck 2018 data yields $|f_R0| < 4.79 ×10^-6$ [ref] .
Disentangling modified gravity and galaxy bias with field-level inference · Modified Gravity: $f(R)$ theories · 0.93
Compares with it 3 papers
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These bounds are in line with current cosmological constraints on the field (e.g. [ref] )[Note that tests at galactic scales [ref] impose more stringent limits of $|f_R,0|≲10^-8$, when a particular model for the $f(R)$ function is adopted.], and provide the limiting precision that can be achieved by kinematics and lensing analysis of clusters.
Mass Modeling and Kinematics of Galaxy Clusters in Modified Gravity · Discussions and conclusions · 0.90
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Such a comparison reveals that these constraints are competitive with the current tightest bounds coming from galactic structure [ref] , which might however be relying on simple assumptions to model the screening effect in galactic settings [ref] .
Towards unveiling the large-scale nature of gravity with the wavelet scattering transform · Results · 0.95
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This is the strongest bound to date on long-range interactions in the dark sector from cosmological data (see Refs. [ref] for constraints from galactic dynamics).
Unveiling dark forces with measurements of the Large Scale Structure of the Universe · Outlook · 0.86
Cites it as background 3 papers
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Much of the recent literature has studied the behaviour of these theories on galactic scales, where the screening phenomenon leads to a rich phenomenology, such as equivalence principle violations and other kinematic signatures [ref] .
Accurate Computation of the Screening of Scalar Fifth Forces in Galaxies · Introduction · 0.98
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Finally, we note that the literature is rich with astrophysical (stellar and galactic) bounds on chameleons, see e.g. Refs. [ref] .
Direct detection of dark energy: the XENON1T excess and future prospects · Stellar cooling constraints · 1.00
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Morphological information has been used to investigate stellar masses [ref] , star formation history [ref] , investigating galaxy color, gas, and dust content [ref] , galaxy age [ref] , studies of dynamical evolution [ref] , and even tests of modified gravity theories [ref] .
Galaxy Morphology Classification: Uncertainty Modeling and Out of Distribution Detection · Introduction · 0.82
What it cites · 60 sentences without a confident label
Contests 1 paper
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An example of the former is a model in which the fifth-force operates only in the dark sector; we conclusively rule out, for example, the $=𝒪(0.1)$ proposed in [ref] .
$H_0$ Tension, Swampland Conjectures and the Epoch of Fading Dark Matter · Results · contest 0.83
Builds on 4 papers
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Building on previous work [ref] , we develop a Monte-Carlo-based technique in the framework of Bayesian statistics to forward-model the signals on a galaxy-by-galaxy basis in a large sample ($𝒪(10^4)$) of galaxies.
Fifth force constraints from galaxy warps · Introduction · 0.92
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Building on previous work [ref] , we develop a Monte-Carlo-based technique in the framework of Bayesian statistics to forward-model the signals on a galaxy-by-galaxy basis in a large sample ($𝒪(10^4)$) of galaxies.
The Fifth Force in the Local Cosmic Web · Introduction · 0.92
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Building on previous work [ref] , we develop a Monte-Carlo-based technique in the framework of Bayesian statistics to forward-model the signals on a galaxy-by-galaxy basis in a large sample ($𝒪(10^4)$) of galaxies.
Reconstructing the gravitational field of the local universe · Introduction · 0.92
Uses the method or tool of 16 papers
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Our detailed methodology for using these images to measure $w_1$ may be found in [ref] sec.
Fifth force constraints from galaxy warps · Data acquisition and reduction · 1.00
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For a set of point masses $j$ this is [equation] at test object $i$. $a⃗_5$ is modelled as a Yukawa force from sources within $4λ_C$ (as opposed to long-range but cut off at $λ_C$, as previously): [equation] These are calculated by modelling the distribution of mass in the local universe using the method of [ref] , as implemented in [ref] (for other approaches see [ref] ).
Astrophysical Tests of Modified Gravity: A Screening Map of the Nearby Universe · Modelling the gravitational and fifth-force fields · 1.00
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For a set of point masses $j$ this is [equation] at test object $i$. $a⃗_5$ is modelled as a Yukawa force from sources within $4λ_C$ (as opposed to long-range but cut off at $λ_C$, as previously): [equation] These are calculated by modelling the distribution of mass in the local universe using the method of [ref] , as implemented in [ref] (for other approaches see [ref] ).
Reconstructing the gravitational field of the local universe · Modelling the gravitational and fifth-force fields · 1.00
Uses data or values from 2 papers
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We derive a sample of gas–star offsets by cross-correlating the 100% dataset of ALFALFA[<http://egg.astro.cornell.edu/alfalfa/>] [ref] with v1_0_1 of the NASA Sloan Atlas (NSA)[<https://www.sdss.org/dr13/manga/manga-target-selection/nsa/>].
The Arecibo Legacy Fast ALFA Survey: The ALFALFA Extragalactic HI Source Catalog · Data acquisition and reduction · 0.94
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We calculated $r⃗_*$ and $w_1$ in a sample of well-resolved galaxies from the $z=0$ snapshot of the Horizon-AGN simulation [ref] , in addition to their stellar and gas masses and sizes, and virial masses.
Dancing in the dark: galactic properties trace spin swings along the cosmic web · Systematic uncertainties · 0.86
Compares with 8 papers
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Although we find no preference here for $>0$ at any $0.3 < λ_C/Mpc < 8$, we confirm the result of [ref] that – with the selection criteria of those analyses – there is a preference relative to GR for a screened fifth force with $λ_C ≃2$ Mpc and $≃0.02$.
Fifth force constraints from the separation of galaxy mass components · Comparison with the literature · 0.98
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Although we find no preference here for $>0$ at any $0.3 < λ_C/Mpc < 8$, we confirm the result of [ref] that – with the selection criteria of those analyses – there is a preference relative to GR for a screened fifth force with $λ_C ≃2$ Mpc and $≃0.02$.
Fifth force constraints from galaxy warps · Comparison with the literature · 0.98
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Our constraints on $$ are almost an order of magnitude stronger than those of [ref] for most $λ_C$ due to the larger sample size, more realistic noise model and combination of warp and gas–star offset warp data.
The Fifth Force in the Local Cosmic Web · Comparison with the literature · 1.00
Cites as background 16 papers
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Further detail on many topics may be found in [ref] .
Fifth force constraints from the separation of galaxy mass components · Introduction · 0.96
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Further detail on many topics may be found in [ref] .
Fifth force constraints from galaxy warps · Introduction · 0.96
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The aim of this paper is to use these signals to set constraints on the strength and range of thin-shell-screened fifth forces, with particular emphasis on the Hu-Sawicki model of $f(R)$ gravity [ref] .
Models of f(R) Cosmic Acceleration that Evade Solar-System Tests · Introduction · 0.86
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