Do gravitons interact with gravitons?

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  • #1
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Do graviton-graviton interactions increase the gravitational binding of matter? Please read summary of "Implications of Graviton-Graviton Interaction to Dark Matter", arXiv:0901.4005v2 Astrophysics.
Specifically, how would graviton-graviton interactions increase the gravitational binding of matter?
I visualize that the beam of spacetime between two stars is very ordered, in that streams of gravitons from each star flow in very nearly anti-parallel paths. Will these gravitons interact?
Light beams do gravitationally interact, but very weakly: arXiv:gr-qc/9811052v1 by Faraoni and Dumse, "The gravitational interaction of light,..."

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  • #2
Nonlinear effects of gravity (interaction between gravitons, in the particle picture) are completely negligible far away from compact objects. Otherwise they would be extremely prominent closer to these dense objects.
I visualize that the beam of spacetime between two stars is very ordered, in that streams of gravitons from each star
That doesn't make sense. Stars don't emit streams of gravitons.
  • #3
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First reference in the OP:

To conclude, the graviton–graviton interaction suggests a mechanism to explain galaxy rotation curves and cluster dynamics.
It seems that the Graviton–Graviton Interaction yields the rotation curves of galaxies quite close to the observation, s. Fig. 3. How does this fit to
Nonlinear effects of gravity (interaction between gravitons, in the particle picture) are completely negligible far away from compact objects.
Is the Graviton-Graviton Interaction the authors are describing well accepted in scientific community?

To detect gravitons seems to be extremely challenging. But isn't it at least an indirect suggestion that - in the light of these calculations - they exist?
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  • #4
I don't trust a model that only works in a single place. If it would work elsewhere, why wouldn't they discuss this?
  • #5
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Indeed, it doesn't seem to be discussed with respect to the CMB, thanks.
  • #6
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I don't trust a model that only works in a single place. If it would work elsewhere, why wouldn't they discuss this?

The paper cited is one of the earliest in a series of papers. Deur's approach has broad applicability (broader than MOND) to all types of galaxies (recognizing diversity in inferred dark matter amounts based upon the shape of ordinary matter distributions in a galaxy), to galaxy clusters including the Bullet Cluster, to the cosmic coincidence effect, to dark energy phenomena, and to the early formation of galaxies and certain other cosmology effects.

I think it has merit. Indeed, while my opinion as a lay person isn't really relevant, I think it is the most promising work on the questions of dark matter, dark energy and modified gravity published to date. If he's right, it is a Nobel Prize class insight, and the fact that several papers on this approach are published in peer reviewed journals (some with co-authors from the relevant field) and that it has made new observational predictions which have been confirmed means that it shouldn't be dismissed out of hand.

No publications or preprints challenge or dispute any of Deur's published work on gravity, and while simply being ignored isn't that praiseworthy, many other published papers purporting to explain dark matter phenomena with negligected non-Newtonian aspects of General Relativity (GR) not used by astronomers in estimating galaxy dynamics, using other aspects of GR, were the subject to quick published refutations. For example, it doesn't overlap at all with the gravitomagnetic effects claimed in G. O. Ludwig, "Galactic Rotation Curve and Dark Matter According to Gravitomagnetism" 81 European Physical Journal C 186 (2021) DOI 10.1140/epjc/s10052-021-08967-3 and by a few earlier authors, which have been criticized. Ludwig looks at the gravitational effects in GR arising from the motion of objects in a rotating galaxy that are neglected in the Newtonian approximation used by most astronomers in estimating galaxy dynamics, which critics argue are orders of magnitude too small to explain galaxy rotation curves. Deur is developing his work in a static approximation that ignores dynamic GR effects such as gravitomagnetism to make the calculations mathematically manageable.

This said, this approach, in part, because its author is primarily a QCD (quantum chromodynamics) physicist, rather than an astrophysicist or GR researcher, hasn't received much attention from other scientists in field: few other scientists have built on it, and no one has seriously examined and critiqued and reviewed it.

A 2014 power point presentation by the author provides a good introduction that is a bit less technical and hits the high points.

Graviton-graviton Interaction is universally accepted in scientific community as something that is present in any quantum gravity theory. See, e.g. Feynman, "Quantum Theory of Gravitation" (1963). See also here. There are gravitational field self-interactions in classical GR as well, although the structure of the typical form of the Einstein equations of GR obscure this effect by treating it differently than other sources of space-time curvature (because gravitational fields are not elements of the stress-energy tensor like other sources of space-time curvature). But the common assumption in the GR field (although not rigorously evaluated) is that this effect is small in galaxy scale systems. And, it is undisputed that it does cancel out in the case of spherically symmetric mass sources, which are the systems most carefully studied theoretically in GR.

Basically, Deur's argument is that this is a second order effect that is negligible near strong sources relative to primary graviton interaction which are much stronger at short distances relative to self-interaction effects, but that self-interaction effects are significant in extremely weak fields relative to primary graviton interactions, because the primary graviton interaction declines with distance proportionate to 1/r2 while the graviton self-interaction effect in a system with a disc-like geometry declines with distance proportionate to 1/r, so at a characteristic weakness of the field strength, the graviton-graviton interaction becomes stronger relative to the primary graviton interaction.

We know from observational tests of MOND (Modified Newtonian Dynamics developed by GR researcher Milgrom in 1983, creating a toy model formula to explain dark matter phenomena that is very well studied), that empirically, observed deviations from Newtonian gravitational approximations (which is what astronomers actually use to do models) which are attributed to dark matter, can be well described as occurring entirely via gravitational modifications in very weak gravitational fields. MOND has also made many ex ante predictions that have been proved correct, although it tends to underestimate dark matter phenomena at galaxy cluster scales and needs to be generalized to a relativistic version to accurately describe strong field gravitational effects, and is purely phenomenological rather than having a theoretical basis.

MOND investigators estimate the strength of the gravitational field below which non-Newtonian effects attributed to dark matter become relevant only in gravitational fields weaker than 1.2 x 10-10 ms-2. How weak is that? Assume that the only source of gravitational fields is the Sun. This is about 1/9th of the light year from the Sun, which is about 175 times the average distance of Pluto from the Sun. Pluto's average distance from the Sun is about 6 billion km). This is about 58 times more distant from the Sun that the heliosphere, which is a functional definition of where the solar system ends and deep interstellar space begins, that is about 18 billion km (120 astronomical units) from the Sun. As of February 2018, Voyager 1, the most distant man made object from Earth, was about 21 billion km from Earth, and Voyager 2, the second most distant man made object from Earth is about 17 billion km from Earth. Both were launched 43 years ago in 1977. These probes (which will run about of power around the year 2025), will reach this distance from the Sun about 2000 years from now in around 4000 CE.

The graviton self-interaction also cancels out if the geometry of the gravitational source is spherically symmetric (which the vast majority of theory papers in GR assume in their analyses at the outset). So, for example, it is almost non-existent in an interaction of a single star and a test mass, or in the vicinity of a nearly spherical elliptical galaxy.

If the mass is confined to a disk, the self-interactions cause the system to reduce from a three dimensional one to a two dimensional one, causing the force to have a 1/r form that we see in the MONDian regime of spiral galaxies.

In the geometries where Deur's approach approximate's MOND, the following formula approximate's the self-interaction term:

FG = GNM/r2 + c2(aπGNM)1/2/(2√2)r

where FG is the effective gravitational force, GN is Newton's constant, c is the speed of light, M is ordinary baryonic mass of the gravitational source, r is the distance between the source mass and the place that the gravitational force is measured, and a is a physical constant that is the counterpart of a0 in MOND (that should in principle be possible to derive from Newton's constant) which is equal to 4*10−44 m−3s2.

Thus, the self-interaction term that modifies is proportionate to (GNM)1/2/r. So, it is initially much smaller that the first order Newtonian gravity term, but it declines more slowly than the Newtonian term until it is predominant.

For two large point masses, you get a QCD flux tube-like solution which makes the self-interaction term stronger and explains why MOND underestimates dark matter phenomena in clusters where the geometry of the mass sources are best described as interacting large point masses.

This isn't the only work recognizing that dark matter phenomena behave differently based upon the shape of the underlying ordinary matter distributions involved. See also, e.g., Lorenzo Posti, S. Michael Fall "Dynamical evidence for a morphology-dependent relation between the stellar and halo masses of galaxies" Accepted for publication in A&A. arXiv:2102.11282 [astro-ph.GA] (February 22, 2021).

As noted below in the relevant papers section of this post, in an excerpt from one of Deur's papers, the CMB has not been worked out in this approach although general observations that suggest it may address the same issues that dark matter does are made. But, notably, a partially relativistic generalization of MOND (which Deur's approach tends to mimic in many systems) has reproduced the CMB of the LambdaCDM Standard Model of Cosmology with a MOND inspired theory.
We propose a relativistic gravitational theory leading to Modified Newtonian Dynamics, a paradigm that explains the observed universal acceleration and associated phenomenology in galaxies. We discuss phenomenological requirements leading to its construction and demonstrate its agreement with the observed Cosmic Microwave Background and matter power spectra on linear cosmological scales. We show that its action expanded to 2nd order is free of ghost instabilities and discuss its possible embedding in a more fundamental theory.
Constantinos Skordis, Tom Złosnik, "A new relativistic theory for Modified Newtonian Dynamics" arXiv (June 30, 2020).

So, it is very plausible the Deur's approach could also produce this result.

Deur's theory is attractive for a variety of reasons:

Observational Evidence Supports Deur's Model

* There is strong evidence, developed in the MOND context (and to a lesser extent in tests of other gravity modification approaches), that dark matter phenomena involved in galactic dynamics can be understood as a modification of conventional Newtonian approximations of gravity used in astronomy. This is in contrast to explanations of dark matter phenomena involving one or more dark matter particles beyond the Standard Model. Because the formula that Deur develops is observationally almost indistinguishable from MOND in spiral galaxies, in the circumstances where MOND works well, his theory benefits from this body of evidence.

* Deur's approach also makes predictions similar to MOND in other contexts. For example, new 21 cm background radiation observations, that are contrary to the predictions of the Lambda-CDM Model, also support Deur's theory.

* Deur's solution elegantly solves the galactic cluster problem of MOND by resorting to the differences in shape of clusters and their subparts, and the geometry between bodies attracted to each other in galactic clusters, and the arrangements of matter found in galaxies. Thus, it cures one of the main short fallings of MOND.

* Deur's solution predicts and explains a previously unnoticed relationship between the apparent amount of dark matter in an elliptical galaxy and the extent to which the galaxy is not spherical, which other modified gravity and dark matter particle theories do not.

* Deur's solution predicts and explains a previously unnoticed relationship between the thickness of a disk galaxy and the apparent amount of dark matter in a disk galaxy.

* This quantum gravity theory overcomes problems arising from observational evidence from correlated visible light and gravitational wave observations of black holes merging with neutron stars that shows that gravitational waves travel at a speed indistinguishable from the speed of light to high precision. This observation is inconsistent with massive gravitons in some modified gravity theories (e.g. many scalar-tensor or scalar-vector-tensor theories), because it utilizes only a single massless graviton.

* The Lambda-CDM Model does a great job of predicting the peaks in the cosmic background radiation of the universe, but does not do a good job of explaining dynamics of galaxies, or explaining why those dynamics are so tightly correlated with the distribution of baryonic matter in those systems. Simple cold dark matter models with a single "sterile" massive fermion do not accurately reproduce the inferred dark matter halos that are observed, nor do many more complicated dark matter particle theories. There are actually myriad discrepancies between observation and predicted behavior in the Lambda-CDM Model at the galaxy scale and some problems even at the galactic cluster scale. This is so even thought the Lambda-CDM Model is incomplete because it doesn't, by itself, explain how the cold dark matter in that matter came to have the very structured distribution that inferred dark matter distributions do observationally. I'll summarize the problems with Lambda-CDM at the bottom of this post.

Deur's Model Is Attractive Theoretically

* Deur explains dark matter and dark energy phenomena as a natural outgrowth of quantum gravity (although while a graviton concept transparently motivates the theory, it isn't inherently non-classical), with no "moving parts" that can be adjusted to make it fit the data in advance (although the relevant constants as applied haven't been worked out from first principles).

* Deur's theory provides a sound theoretical basis for an explanation of the dark matter phenomena with modifications of the Newtonian gravity approximation widely used in large scale astronomy contexts, that it utilizes, because it derives these modifications from first principles. It does so in a way that sidesteps the overwhelming calculation difficulties of doing the full fledged calculations of gravity with a spin-2 massless graviton that has been an insurmountable barrier to other quantum gravity theories, but without inducing significant systemic error in the systems to which the theory is applies (i.e. the differences between a spin-0 graviton theory and a spin-2 graviton theory in dark matter and dark energy contexts is slight except in gravitational systems that are far from equilibrium). It is not mere numerology or a purely phenomenological theory.

* While Deur's approach does not reproduce the conclusions of General Relativity as conventionally applied in the weak gravitational fields and spherically asymmetric systems where it dark matter and dark energy phenomena are observed, he does not make any assumptions about the properties of the graviton which are not utterly vanilla in the context of graviton based quantum gravity theories. None of the underlying assumptions from which this approach is derived contradict the underlying assumptions associated with General Relativity.

* Deur's approach builds on the common quantum gravity paradigm of gravity as QCD squared (strictly speaking Yang-Mills squared, but QCD is an SU(3) Yang–Mills theory).

* Basically, if Deur's approach ends up being correct, then the way that gravitational field self-interactions are incorporated into General Relativity in the Einstein's equations as conventionally applied are subtly flawed. This also explains why quantum gravity researchers trying to build a quantum gravity theory that exactly reproduces Einstein's equations as conventionally applied have failed. They have tried to reproduce a slightly erroneous operationalization of General Relativity, and the theoretical difficulties with doing this become more apparent in the quantum gravity context.

* Deur's background as a professional QCD scientist pretty much assures that his non-abelian gauge field mathematics are sound. Independent efforts corroborate the validity of the main simplification he makes relative to quantum gravity with a spin-2 massless graviton by using a static scalar graviton approximation (see, e.g. Diogo P. L. Bragança, José P. S. Lemos “Stratified scalar field theories of gravitation with self-energy term and effective particle Lagrangian” (June 29, 2018) (open access) (pre-print here)).

* Deur's solution is pretty much the simplest possible resolution of the problems of quantum gravity, dark matter and dark energy, because (1) it does so with no new particles (other than the graviton found in all quantum gravity theories), (2) no new forces, and (3) one fewer fundamental physical constants than the existing core theory of the Standard Model and General Relativity (without dark matter).

* The ΛCDM Model, also known as the Lambda-CDM Model, also known as the Standard Model of Cosmology, requires that 97.8% of the mass-energy of the universe be made up of never observed dark matter and dark energy, while Deur's theory relies entirely on Standard Model fundamental particles and massless gravitons.

* Many modified gravity theories assume new scalar and vector fields in addition to the tensor field of the graviton. Many dark matter particle theories require a new self-interaction force between dark matter particles or a new force governing interactions between dark matter and ordinary matter, or both. Deur's theory, in contrast, gives rise to no new forces or fields.

* This quantum gravity theory, in principle, replaces the three constants of general relativity plus MOND (Newton's constant G, the cosmological constant λ, and the MOND universal acceleration, a0) and replaces them with a single fundamental constant, the gravitational coupling constant (whose value has already been measured moderately precisely). This coupling constant is basically Newton's constant G, although possibly in different units. Both the cosmological constant and the universal acceleration constant of MOND can be derived, in principle, from G in this theory (although he has not done this derivation himself). In contrast, MOND adds one physical constant to the existing core theory, and dark matter adds at least one dark matter particle mass (and more masses in the dark matter sector such as a mass and coupling constant for a dark boson that carries a self-interaction or ordinary matter-dark matter interaction or both, are present in many versions of dark matter theories), one dark matter abundance constant, and other properties related to the dark matter particle. Modified gravity theories other than MOND (such as Moffat's MOG theory) often have even more new physical constants than MOND does.

* Deur's theory harmonizes gravity and the Standard Model with no particles beyond the Standard Model other than the massless graviton. The deep theoretical inconsistencies of the two models that make up core theory are eliminated (almost). Deur's formulation of the theory as a quantum field theory simplifies its integration as a quantum gravity theory with the Standard Model, which is also a quantum field theory.

* Deur's theory explains the cosmic coincidence problem in a very natural way.

* Deur's theory solves the conservation of mass-energy problem with general relativity's cosmological constant solution to "dark energy." Conventional general relativity theory, in contrast, accepts that gravitational energy is only conserved locally and not globally. In Deur's theory, dark energy arises from self-interacting gravitons staying within the galaxy at rates higher than they would in the absence of self-interactions which causes mass of the edge of a galaxy to be pulled more tightly towards the galaxy. Because these gravitons leave the galaxy at a rate lower than they would in the absence of self-interactions, the gravitational pull between galaxies is weaker than it would be in the absence of gravitational self-interaction. Thus, dark energy is due to a weaker pull between galaxies than in the Newtonian or cosmological constant free general relativity model, rather than due to having something pervasive in space pulling apart distant objects.

* Deur's theory is not plagued with tachyons, causation violations, ghosts, unitarity violations and similar defects that are common in efforts to modify gravity.


The related papers are:

The non-abelian symmetry of a lagrangian invalidates the principle of superposition for the field described by this lagrangian. A consequence in QCD is that non-linear effects occur, resulting in the quark-quark linear potential that explains the quark confinement, the quarkonia spectra or the Regge trajectories. Following a parallel between QCD and gravitation, we suggest that these non-linear effects should create an additional logarithmic potential in the classical newtonian description of gravity. The modified potential may account for the rotation curve of galaxies and other problems, without requiring dark matter.

A. Deur, “Non-Abelian Effects in Gravitation” (September 17, 2003) (pre-print not published).

Our present understanding of the universe requires the existence of dark matter and dark energy. We describe here a natural mechanism that could make exotic dark matter and possibly dark energy unnecessary. Graviton-graviton interactions increase the gravitational binding of matter. This increase, for large massive systems such as galaxies, may be large enough to make exotic dark matter superfluous. Within a weak field approximation we compute the effect on the rotation curves of galaxies and find the correct magnitude and distribution without need for arbitrary parameters or additional exotic particles. The Tully-Fisher relation also emerges naturally from this framework. The computations are further applied to galaxy clusters.
A. Deur, “Implications of Graviton-Graviton Interaction to Dark Matter” (May 6, 2009) (published at 676 Phys. Lett. B 21 (2009)).

We discuss the correlation between the dark matter content of elliptical galaxies and their ellipticities. We then explore a mechanism for which the correlation would emerge naturally. Such mechanism leads to identifying the dark matter particles to gravitons. A similar mechanism is known in Quantum Chromodynamics (QCD) and is essential to our understanding of the mass and structure of baryonic matter.
Alexandre Deur, “A correlation between the amount of dark matter in elliptical galaxies and their shape” MNRAS, 438, 1535 (July 28, 2014) .

We study two self-interacting scalar field theories in their high-temperature limit using path integrals on a lattice. We first discuss the formalism and recover known potentials to validate the method. We then discuss how these theories can model, in the high-temperature limit, the strong interaction and General Relativity. For the strong interaction, the model recovers the known phenomenology of the nearly static regime of heavy quarkonia. The model also exposes a possible origin for the emergence of the confinement scale from the approximately conformal Lagrangian. Aside from such possible insights, the main purpose of addressing the strong interaction here --given that more sophisticated approaches already exist-- is mostly to further verify the pertinence of the model in the more complex case of General Relativity for which non-perturbative methods are not as developed. The results have important implications on the nature of Dark Matter. In particular, non-perturbative effects naturally provide flat rotation curves for disk galaxies, without need for non-baryonic matter, and explain as well other observations involving Dark Matter such as cluster dynamics or the dark mass of elliptical galaxies.

A. Deur, “Self-interacting scalar fields at high temperature” (June 15, 2017) (published at Eur. Phys. J. C77 (2017) no.6, 412).

Numerical calculations have shown that the increase of binding energy in massive systems due to gravity's self-interaction can account for galaxy and cluster dynamics without dark matter. Such approach is consistent with General Relativity and the Standard Model of particle physics. The increased binding implies an effective weakening of gravity outside the bound system. In this article, this suppression is modeled in the Universe's evolution equations and its consequence for dark energy is explored. Observations are well reproduced without need for dark energy. The cosmic coincidence appears naturally and the problem of having a de Sitter Universe as the final state of the Universe is eliminated.
A. Deur, “A possible explanation for dark matter and dark energy consistent with the Standard Model of particle physics and General Relativity” (last revised October 22, 2019) (Proceeding for a presentation given at Duke University, Apr. 2014. Based on A. D. PLB B676, 21 (2009); A.D, MNRAS, 438, 1535 (2014). The published version is Eur. Phys. J. C 79, 883 (2019). The body text in this paper notes in one pertinent part:


Predicting the CMB and BAO is complex and model dependent, with many parameters. Like for large structure formation, a detailed investigation is beyond the scope of this article. However, one can remark that since the CMB main acoustic peak position depends on the Universe dynamical evolution, its calculation should involve Ω∗ M rather than ΩM: θ ' p Ω∗ M/zrec (with zrec ' 1100 the redshift at the recombination time). This yields θ ' 0.8 ◦ , in agreement with observations [16].

The end note citation is to G. Hinshaw et al., Astrophys. J. Suppl. 208, 19 (2013).

The discrepancy between the visible mass in galaxies or galaxy clusters, and that inferred from their dynamics is well known. The prevailing solution to this problem is dark matter. Here we show that a different approach, one that conforms to both the current Standard Model of Particle Physics and General Relativity, explains the recently observed tight correlation between the galactic baryonic mass and its observed acceleration. Using direct calculations based on General Relativity's Lagrangian, and parameter-free galactic models, we show that the nonlinear effects of General Relativity make baryonic matter alone sufficient to explain this observation.
A. Deur, Corey Sargent, Balša Terzić, "Significance of Gravitational Nonlinearities on the Dynamics of Disk Galaxies" (August 31, 2019, last revised May 18, 2020) (pre-print) Published ApJ 896 94 (June 17, 2020).

Observations indicate that the baryonic matter of galaxies is surrounded by vast dark matter halos, which nature remains unknown. This document details the analysis of the results published in MNRAS 438, 2, 1535 (2014) reporting an empirical correlation between the ellipticity of elliptical galaxies and their dark matter content. Large and homogeneous samples of elliptical galaxies for which their dark matter content is inferred were selected using different methods. Possible methodological biases in the dark mass extraction are alleviated by the multiple methods employed. Effects from galaxy peculiarities are minimized by a homogeneity requirement and further suppressed statistically. After forming homogeneous samples (rejection of galaxies with signs of interaction or dependence on their environment, of peculiar elliptical galaxies and of S0-type galaxies) a clear correlation emerges. Such a correlation is either spurious --in which case it signals an ubiquitous systematic bias in elliptical galaxy observations or their analysis-- or genuine --in which case it implies in particular that at equal luminosity, flattened medium-size elliptical galaxies are on average five times heavier than rounder ones, and that the non-baryonic matter content of medium-size round galaxies is small. It would also provides a new testing ground for models of dark matter and galaxy formation.
A. Deur, "A correlation between the dark content of elliptical galaxies and their ellipticity" (October 13, 2020) (pre-print).

We present a method to investigate the effect of relativistic corrections arising from large masses to the rotation curves of disk galaxies. The method employs a mean-field approximation and gravitational lensing. Applying it to a basic model of disk galaxy, we find that these corrections become important and magnified at large distances. The magnitude of the effect is sufficient to explain the galactic missing mass problem without requiring a significant amount of dark matter. A prediction of the model is that there should be a strong correlation between the inferred galactic dark mass and the galactic disk thickness. We use two independent sets of data to verify this.
Alexandre Deur, "Relativistic corrections to the rotation curves of disk galaxies" (April 10, 2020) (lated updated February 8, 2021 in version accepted for publication in Eur. Phys. Jour. C).

See also:
We investigate the possible existence of graviballs, a system of bound gravitons, and show that two gravitons can be bound together by their gravitational interaction. This idea connects to black hole formation by a high-energy 2→N scattering and to the gravitational geon studied by Brill and Hartle. Our calculations rely on the formalism and techniques of quantum field theory, specifically on low-energy quantum gravity. By solving numerically the relativistic equations of motion, we have access to the space-time dynamics of the (2-gravitons) graviball formation. We argue that the graviball is a viable dark matter candidate and we compute the associated gravitational lensing.
B. Guiot, A. Borqus, A. Deur, K. Werner, "Graviballs and Dark Matter" 11 JHEP 159 (June 3, 2020 revised September 3, 2020).
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  • #7
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Continuing the previous post, in evaluating the weight given to alternatives to the status quo one also needs to be weighed in light of Lambda-CDM, which has a multitude of problems, any one of which would be troubling, but which collectively points strongly to a major problem of crisis proportions with the paradigm of the so called "Standard Model of Cosmology."

* The gravitational lensing of subhalos in galactic clusters recently observed to be much more compact and less "puffy" than LambdaCDM would predict.
* A KIDS telescope observation of very large scale structure which shows it to be 8.3% smoother (i.e. less clumpy) than predicted by LambdaCDM.
* The Hubble tension that shows that Hubble's constant, which is a measure of the expansion rate of the universe, is about 10% smaller when measured via cosmic microwave background radiation (with a small margin of error) than when measured by a wide variety of measures at times much more removed from the Big Bang that the time at which the cosmic microwave background came into being.
* The DM halo shapes that LambdaCMD predicts are usually wrong (too cuspy and not in the NFW distribution predicted by the theory).
* The correspondence between the distribution of ordinary matter and inferred dark matter in galaxies is too tight; truly collisionless dark matter should have less of a tight fit in its distribution to ordinary matter distributions than is observed. This is also the case in galaxy clusters.
* It doesn't explain systemic variation in the amount of apparent dark matter in elliptical galaxies, or why spiral galaxies have smaller proportions of ordinary matter than elliptical galaxies in same sized inferred dark matter halos, or why thick spiral galaxies have more inferred dark matter than thin ones.
* It doesn't explain why satellite galaxies are consistently located in a two dimensional plane relative to the core galaxy.
* Not as many satellite galaxies are observed as predicted, or why the number of satellite galaxies is related to budge mass in spiral galaxies.
* The aggregate statistical distribution of galaxy types and shapes, called the "halo mass function" is wrong.
* Galaxies are observed sooner after the Big Bang than expected.
* The temperature of the universe measured by 21cm background radio signals is consistent with no dark matter and inconsistent with sufficient dark matter for LambdaCDM to work.
* Observations are inconsistent with the "Cosmological principle" that LambdaCDM predicts, which is "the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale.
* It doesn't do a good job of explaining the rare dwarf galaxies (that are usually dark matter dominated) that seem to have no dark matter.
* It doesn't explain deficits of X-ray emissions in low surface brightness galaxies.
* It predicts too few galaxy clusters.
* It gets globular cluster formation wrong.
* It doesn't explain evidence of stronger than expected gravitational effects in wide binary stars.
* There are too many galaxy clusters colliding at speeds that are too high relative to each other.
* It doesn't explain the "cosmic coincidence" problem (that the amount of ordinary matter, dark matter and dark energy are of the same order of magnitude at this moment in the history of the Universe since the Big Bang).
* There are potential unresolved systemic problems in current dark energy measurements.
* Every measure of detecting it directly has come up empty (including not just dedicated direct detection experiments but particle collider searches, searches for cosmic ray signals of dark matter annihilation, and indirect searches combined with direct searches). But it requires particles and forces of types not present in the Standard Model or general relativity to fit what is observed.
* It has made very few ex ante predictions and those it has made have often been wrong, while MOND has a much better track record despite being far simpler.
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