A LQG Legend Writes Paper Claiming GR Explains Dark Matter Phenomena

[ohwilleke]

{ My head hurts, my head hurts, my head hurts... }

That is the joy of BSM physics! No other reason to do it really.

Does any of these support or falsify the few String Theory versions using Teleparallel Gravity ??

Not really. All of them assume basic GR and not the teleparallel gravity twist on GR.

If one or more of these work, however, it tends to weakens one of the motivations for String Theory, which is to provide a dark matter candidate particle. indeed, some narrow sense Sting Theory investigators claim that the low energy approximation of String Theory must be Supersymmetry, and one of the big arguments for the desirability of BSM Supersymmetry physics has been that it created a dark matter particle candidate. But, if it turns out that dark matter isn't necessary because it is really a GR effect, then this makes new particles that could fill out a dark sector a problem rather than a solution.

 

[mitchell porter]

like Deur, have not triggered refutation papers

I have a feeling there are far more papers with mistakes out there, than there are papers specifically spelling out the mistakes...

Anyway: the issue with all the papers in this thread, or the counterintuitive claim that they share, is the claim of strong GR effects in circumstances where (as Ciotti explains) one only expects weak effects. Any search for a mistake in a specific paper, needs to start by identifying what the alleged mechanism of the strong effects is. For example, in Ludwig it's a gravitomagnetic force that's a million times greater than what you would normally expect (I get this factor from the calculation by Garrett Lisi).

How about Deur? In "Significance of Gravitational Nonlinearities on the Dynamics of Disk Galaxies", Deur et al say:

... one may question the relevance of field self-interaction at large galactic radii r. At these distances, the missing mass problem is substantial, while the small matter density should make the self-interaction effects negligible. The answer is in the behavior of the gravitational field lines; once they are distorted at small r due to the larger matter density, they evidently remain so even if the matter density becomes negligible (no more field self-interaction, i.e., no further distortion of the field lines), preserving a form of potential different from that of Newton. Thus, even if the gravity field becomes weak, the deviation from Newton’s gravity remains.

When it comes to understanding the specific mechanism that Deur proposes, I feel that the key paper is "Self-interacting scalar fields at high temperature". He constructs scalar field theories meant to resemble QCD and GR, and argues that the force potentials they contain will have the same form in the more complex theories. That argument is certainly a natural point of scrutiny - the full theories have extra degrees of freedom, and that can completely change the dynamics.

 

[malawi_glenn]

one of the motivations for String Theory, which is to provide a dark matter candidate particle

Never read that in my string theory books.
Supersymmetric QFT particle models however can provide dark matter candidates, in some region of the models parameter spaces, but they do not have to do that per se.

some narrow sense Sting Theory investigators claim that the low energy approximation of String Theory must be Supersymmetry, and one of the big arguments for the desirability of BSM Supersymmetry physics has been that it created a dark matter particle candidate

What is a string theory "investigator"? Not someone who is a researcher? Who are these narrow sense people, and why are they narrow sensed? Supersymmetry is required in string theory to accommodate fermion particles in the low energy limit, not dark matter candidates.

 

[ohwilleke]

What is a string theory "investigator"? Not someone who is a researcher?

An investigator is basically a scientist but might include, for example, a mathematician who doesn't identify as a scientist. I chose the word to avoid using the word "scientist" for that reason. Researcher means the same thing.

Who are these narrow sense people, and why are they narrow sensed?

The narrow sense people are the people who are working directly with M-theory equations and have a very specific technical definition of what counts as string theory and this definition typically mandates supersymmetry as the low energy limit.

The broad sense people, who also often call themselves string theorists, are people who use concepts from string theory, like a massless spin-2 graviton, or 11 dimensional space, or a minimum sized one dimensional particle, or computational methods, but don't necessarily put it in the context of a specific overall comprehensive theoretical structure intended to be a complete Theory of Everything.

Supersymmetry is required in string theory to accommodate fermion particles in the low energy limit, not dark matter candidates.

Supersymmetry, by definition, supplies BSM fundamental particles. They don't always provide dark matter candidates and that wasn't the original justification for supersymmetry. But supersymmetry advocates generally touts the existence of dark matter candidates as one of the reasons to take the theory seriously and to find it desirable to pursue. If one or more of the supersymmetric fundamental particles cannot decay to SM particles, the lightest supersymmetric particle (LSP) is a prime dark matter candidate (although less so now that direct detection experiments have ruled out supersymmetric WIMPS since supersymmetric WIMPS have to interact via the weak force at the same strength as a neutrino).

Now that supersymmetric particles haven't been discovered at the masses where they would be expected to address the hierarchy problem that motivated supersymmetry in the first place, the feature that they generically provide DM candidates has become much more important in making the case of supersymmetry and by association, string theory.

 

[ohwilleke]

When it comes to understanding the specific mechanism that Deur proposes, I feel that the key paper is "Self-interacting scalar fields at high temperature". He constructs scalar field theories meant to resemble QCD and GR, and argues that the force potentials they contain will have the same form in the more complex theories. That argument is certainly a natural point of scrutiny - the full theories have extra degrees of freedom, and that can completely change the dynamics.

This would seem like more of a concern if the same result weren't reproduced with classical GR.

 

[malawi_glenn]

An investigator is basically a scientist but might include, for example, a mathematician who doesn't identify as a scientist. I chose the word to avoid using the word "scientist" for that reason. Researcher means the same thing.

Use standard lingo instead.

Supersymmetry, by definition, supplies BSM fundamental particles.

Yes but that is residual. You made it sound like (super)string theory was motivated by the need of having a dark matter particle candidate.

 

[ohwilleke]

Use standard lingo instead.

investigator is very standard lingo. I've lived in and around academia since I was a toddler. It is used all the time.

Yes but that is residual. You made it sound like (super)string theory was motivated by the need of having a dark matter particle candidate.

I said, "it tends to weakens one of the motivations for String Theory, which is to provide a dark matter candidate particle" and it is one of the modern motivations for String Theory.

 

[malawi_glenn]

it is one of the modern motivations for String Theory

I guess I have to contact my old friends at the university again and make them list the top 5 motivations for string theory. What does "modern" mean in this context?
My newest String Theory book is from 2012 (Peter Wests book), is there any newer I should get you think?

 

[ohwilleke]

I guess I have to contact my old friends at the university again and make them list the top 5 motivations for string theory. What does "modern" mean in this context?
My newest String Theory book is from 2012 (Peter Wests book), is there any newer I should get you think?

It is a motivation in arguments that there is any observational support for thinking that there is an observational evidence to motivate BSM physics that Sting Theory could explain, and hence for taking it seriously. I agree that it didn't motivate the initial formulation of the theory.

 

[mitchell porter]

This would seem like more of a concern if the same result weren't reproduced with classical GR.

Are you referring to "Relativistic corrections to the rotation curves of disk galaxies"?

Deur says in the summary that the method in this paper is "less directly based on GR’s equations than the path integral approach" (the latter refers to lattice calculations of the kind discussed in the "scalar fields" paper). He describes this new method as "a mean-field technique combined with gravitational lensing". I haven't quite figured out how it works. Although he talks about curvature, I don't see a metric anywhere in the paper.

From what I can see, he models the galaxy as a disk-shaped distribution of mass, then calculates how lines of flight radiating outward from the center would be warped by this mass distribution, then says that this is how gravitational field lines would behave due to self-interaction, and calculates a gravitational force from the flux of field lines. There must be a way of judging whether this is what GR actually predicts... At least Deur's paradigm is getting clearer to me now.

 

[malawi_glenn]

It is a motivation in arguments that there is any observational support for thinking that there is an observational evidence to motivate BSM physics that Sting Theory could explain, and hence for taking it seriously. I agree that it didn't motivate the initial formulation of the theory.

Do you have any other source where a string theorist lists dark matter particle candidate as a modern motivation?

 

[kodama]

Do you have any other source where a string theorist lists dark matter particle candidate as a modern motivation?

Brian Green and Michio Kaku mention WIMPS and dark matter in their popular books

 

[malawi_glenn]

Brian Green and Michio Kaku mention WIMPS and dark matter in their popular books

I am sure they do, but popular books are ... well ... not a good source of information ...
Let's say I want to fund a string theory research (investigation) group, and I need to write a funding proposal. Should I use those books as a source?

Remember the movie "limitless"? Where the main characters friend /or was it sister...) said he/she read Brian Greenes book in just one day? Why not read GREENs books on Superstring theory? The real deal so to say. I just thought this was a fun anectode.

 

[Davephaelon]

When I first came across Deur's work based on self-interacting gravitons, in analogy with QCD, I was astounded by its elegant simplicity in explaining, for example, the excess orbital velocities of galaxies within a galaxy cluster. Here he invokes flux tubes to account for the additional gravitational attraction between 'point like' galaxies above what would be expected in classical Newtonian gravity. But as evidenced by gravitational lensing a cluster's gravity is enhanced beyond its periphery. It struck me that the extra gravitational potential from the flux tube mechanism would only apply between galaxies but not add to the gravity potential beyond the cluster. It's inconceivable that professor Deur could have overlooked this, so the explanation is probably in one of his papers, which are pretty technical. I'm a bit groggy this morning, but will check later in the morning Ohwilleke's excellent, more layman friendly, write-up on Deur's work to see if I can find something on this.

 

[Davephaelon]

Oops, I see that I already made a query on the issue of explaining enhanced gravity from lensing data beyond the outer boundaries of both galaxies and galaxy clusters, in Deur's SI paradigm, on the thread titled "Do gravitons interact with gravitons". Scanning the responses over there, I see that there is a stackexchange write-up in the last post linked by rcarbajal68 that addresses this issue. I'll give that a lookover.

 

[mitchell porter]

I continue to think it's extremely unlikely that general relativity actually predicts what Deur says it predicts.

More precisely:

@ohwilleke is our best authority on Deur's work. He says (#65 in this thread) that Deur claims these effects occur even in the classical theory. I tried to work out the alleged mechanism in #70.

It must be possible to judge whether this is a reasonable claim, even without exact solutions. Hawking and Penrose proved their singularity theorems by reasoning about geodesics. Surely there's some way to place bounds on what amplified nonlinearity in classical GR can accomplish (perhaps something involving Lyapunov exponents?).

Then there's the quantum version of Deur's arguments. Here the paper I mention in #62 might contain the detailed arguments. Again I am skeptical - yes, gravitons should interact with gravitons, but the interaction ought to be extraordinarily weak, because of the extreme smallness of the gravitational coupling constant. Maybe there's more opportunity for extremely strong nonperturbative effects, e.g. if the gravitational coupling constant runs to large values at small enough scales.

But overall I'm still skeptical here, too. If I ever get around to checking, I might start by investigating whether the approximation of a tensor field (the metric) by a scalar, is messing up the dynamics by introducing an unjustified constraint. (Reducing a tensor to a scalar is a massive truncation of the physical state space, and needs to have a dynamical justification, i.e. there needs to be some cause actively preventing the other degrees of freedom from acquiring forbidden values.)

By the way, what I'm saying is not quite the same as saying that Deur is completely wrong. His calculations could be wrong in general relativity (classical or quantum), but might be right in some other theory of gravity.

 

[ohwilleke]

I continue to think it's extremely unlikely that general relativity actually predicts what Deur says it predicts.

Fair. I certainly don't have the capacity to evaluate that rigorously. There are quite a few papers that he has published in peer reviewed journals and he is a professional full time physicist, so surely this work isn't wildly off the mark. But GR is notorious for being an area where very subtle issues of characterization can make a big difference.

By the way, what I'm saying is not quite the same as saying that Deur is completely wrong. His calculations could be wrong in general relativity (classical or quantum), but might be right in some other theory of gravity.

This is indeed an important point. If you've got gravitational equations that can describe phenomena attributed to dark matter and dark energy over a very great range of applicability, is relativistic in the general sense, can reproduce the CMB and address issues like the impossible early galaxies problem, even if it deviates from Einstein's Field Equations as conventionally applied, then Deur still has a winner, even if he somewhat misunderstands the nature of why his calculations work, and Einstein's Field Equations are probably not quite the right description of reality even though they are really close and excellent in some domains of applicability like strong gravitational fields.

The possibility that the results are really primarily a quantum gravity specific effect are among the possibilities that could make sense.

On the other hand, it is frustrating that there isn't more third-party examination of what is really one of the most promising dark matter particle theory alternatives, to vet it and consider it. The more there are published papers that are not refuted, the more he gets co-authors and publication in peer reviewed articles, and the more that dark matter particle theories and LambdaCDM fall short, the more this work deserves expert attention from GR specialists.

 

[ohwilleke]

There has been plenty of research on nonlinearity in general relativity; there has been plenty of research on stress-energy pseudotensors and partially localized definitions of energy; are there really dramatic new empirical consequences waiting to be revealed, once these two lines of research are considered together?... I also want to understand the relationship between the classical and quantum parts of Deur's research. Hopefully all this can be disentangled with sufficient patience and care.

Another thing that has impeded existing research is that the vast majority of GR papers, in order to make their analytical calculations tractable, assume spherically symmetrical systems, which when present, automatically eliminate the self-interaction effects (which makes sense if conventional wisdom tells you that effects from lack of spherically symmetry aren't important and leading textbooks say so in so many words).

One of the reasons Deur investigated non-sphericially symmetric systems, which GR researchers avoid for convenience in a very large share of work examining how conventional GR as opposed to modifications of it work, is that in QCD (which is his primary specialty in physics) you simply can't do that and get useful results, so he's used to strategies for modeling non-spherically symmetric systems mathematically with which the run of the mill GR researcher is not.

 

[timmdeeg]

This whole discussion doesn't seem to clarify how Deur's gravitational field self-interaction really works.

Apart from this the predictions regarding CMB and Supernovae data are astonishing:

FIG. 2: Power spectrum of the CMB temperature anisotropy FIG. 3: Left panel: Supernova apparent magnitudes vs. redshift.

I wonder if what he calls "the present calculation" shouldn't yield the values of the Hubble "constant" for the early universe und for our local universe too.

Does anyone know if and how Deur's work contributes to resolve the ongoing Hubble-Tension?

 

[ohwilleke]

Does anyone know if and how Deur's work contributes to resolve the ongoing Hubble-Tension?

He hasn't written on the topic yet.

The Hubble constant is not definitionally constant in his work, as phenomena attributed to dark energy in his work are emergent from the emergence of galaxy and large scale structure rather than than being closely related to a cosmological constant term in the equations of GR. So, it might resolve the tension and at a minimum, some sort of tension wouldn't be surprising in his work.

 

[timmdeeg]

He hasn't written on the topic yet.

The Hubble constant is not definitionally constant in his work, as phenomena attributed to dark energy in his work are emergent from the emergence of galaxy and large scale structure rather than than being closely related to a cosmological constant term in the equations of GR. So, it might resolve the tension and at a minimum, some sort of tension wouldn't be surprising in his work.View attachment 315023

http://link.springer.com/content/pdf/10.1140/epjc/s10052-019-7393-0.pdf
Equation (17) yields for present time: 1 = [DM (0)ΩM + DRΩR + DΛΩΛ] − K a2 0 H2 0 , (22)

Sorry I didn't transfer this into Latex.

(17) yields the present time (late universe) Hubble constant expressed by the depletion function$D_M$, whereby $\Omega_R=0$ and $\Omega_{\Lambda}=0$ .

Deur doesn't show a value for $H_0$ explicitly. As he reproduces the supernovae data correctly would this imply the correctness of the late universe Hubble constant, presently around 73 (km/s)/Mpc?

But what if it turns out that the supernovae distance ladder has some systematic failure and thus $H_0$ changes accordingly. Would this eventually support Deur's self-interaction Hypothesis?

 

[ohwilleke]

http://link.springer.com/content/pdf/10.1140/epjc/s10052-019-7393-0.pdf
Equation (17) yields for present time: 1 = [DM (0)ΩM + DRΩR + DΛΩΛ] − K a2 0 H2 0 , (22)

Sorry I didn't transfer this into Latex.

(17) yields the present time (late universe) Hubble constant expressed by the depletion function$D_M$, whereby $\Omega_R=0$ and $\Omega_{\Lambda}=0$ .

Good catch.

Deur doesn't show a value for $H_0$ explicitly. He reproduces the supernovae date correctly. Would this imply the correctness of the late universe Hubble constant, presently around 73 (km/s)/Mpc?

But what if it turns out that the supernovae distance ladder has some systematic failure and thus $H_0$ changes accordingly. Would this eventually support Deur's self-interaction Hypothesis?

It would take a lot more careful analysis and review of that paper for me to tell. Deur's approach does address consistently with the evidence and contrary to LambdaCDM address the impossible early galaxies problem as well as CMB, so it may very well be consistent.

 

[kodama]

He hasn't written on the topic yet.

if dark matter is discovered and explains everything it is said to does that mean Deur is wrong

 

[ohwilleke]

if dark matter is discovered and explains everything it is said to does that mean Deur is wrong

Yes. That would be awesome if it happened. I don't think it will in the next three decades or so.

 

[kodama]

Yes. That would be awesome if it happened. I don't think it will in the next three decades or so.

sterile neutrinos, axions, wimps, even black hole and x17-z'

 

[timmdeeg]

It would proof that Deur's GR field self-interaction mimicking several times the amount of baryonic matter isn't more than a notion but a wrong one.

It seems in GR there is no rigorous calculation instead there is the analogy to QCD whereby Deur refers to a similarity of the Lagrangian. Whereas in QCD the field-interaction exists and is described undoubtedly.

I'm not sure about this: Would field-self-interaction in GR necessarily imply the existence of gravitons?

Is all this the weak point which causes silence in the community?

 

[Davephaelon]

I am greatly impressed by Deur's hypothesis, inasmuch as it conforms to Occam's Razor of minimal assumptions yielding maximum explanatory power. It's remarkable that with gravitational self-interaction alone one can resolve most of the puzzles that have confronted astrophysicists tracing back almost a century. But I say this as one who doesn't have a deep understanding of GR, so I cannot gauge whether his extrapolation of QCD phenomena into the cosmic arena is fully valid. Hopefully, physicists who are specialists in GR will examine his papers and provide us a more rigorous assessment of the plausibility of the ideas expressed in them.

 

[timmdeeg]

if dark matter is discovered and explains everything it is said to does that mean Deur is wrong

Or the other way round. Would dark matter be disproved if astronomers discover that what seems to be dark matter depends on symmetry properties of a matter distribution as predicted by Deur's field self-interaction SI?

... the expectation that GR field selfinteraction effects cancel for spherically symmetric distributions ...

In contrast in flat galaxies SI doesn't cancel mimicking a large amount of dark matter hence.

 

[ohwilleke]

It seems in GR there is no rigorous calculation instead there is the analogy to QCD whereby Deur refers to a similarity of the Lagrangian. Whereas in QCD the field-interaction exists and is described undoubtedly.

There are calculations using a mean-field approximation of classical GR fields and using the GR Lagrangian, in a static approximation (i.e. ignoring particle momentum contributions and electromagnetic flux contributions to the mass-energy tensor on the right hand side of Einstein's equations). QCD motivates the approach taken but isn't actually being used at all to make the calculations.

As a practical matter, it isn't possible to calculate GR effects analytically (i.e. by working out equations rather than doing N-body calculations or some other numerical method) in complex systems like a galaxy.

I'm not sure about this: Would field-self-interaction in GR necessarily imply the existence of gravitons?

No.

Is all this the weak point which causes silence in the community?

Probably not. More likely it is due to (1) the fact that Deur is primarily a QCD physicist publishing outside his primary subfield community in a different subfield of physics (the astronomy of galaxies, GR, and astrophysics), and (2) that non-rigorously derived conventional wisdom in GR is that non-Newtonian GR effects are negligible in galaxy and galaxy cluster scale systems.

 

[ohwilleke]

sterile neutrinos, axions, wimps, even black hole and x17-z'

Narrow sense WIMPs (e.g. supersymmetric WIMPs), and primordial black holes are basically entirely ruled out by existing observations.

Previous experimental hints of sterile neutrinos have likewise been all but ruled out and have found alternative explanations, although neutrino physics researchers continue to look for sterile neutrinos as explanations for new anomalies. Right handed neutrino theories are also exceedingly popular among theorists trying to devise grand unified theories, and among physicists proposing see saw mechanism for neutrino mass.

Any sterile neutrino dark matter candidate has to propose a creation method for them other than thermal freeze out, because something with a sterile neutrino mass suggested by neutrino research would give rise to "hot dark matter" which is inconsistent with the amount of galaxy scale structure observed.

Also, generically, even if sterile neutrinos (or any more massive DM particle) had mean velocities consistent with warm dark matter or cold dark matter, any dark matter particle solution needs to have some kind of self-interaction and/or interaction with ordinary matter sufficient to explain the dark matter halo shapes/distributions that are inferred from astronomy observations. Without that you get NFW halo distributions which are contrary to astronomy observations, and you don't explain the tight link between inferred DM distributions and observed baryonic matter distributions. These problems are generically a problem with a wide array of particle dark matter candidates.

The X17 boson proposed to explain some subtle kinematics of nuclear matter decays interacts too strongly with other matter to be a dark matter candidate.

Likewise, a Z' boson with a different mass than a Z boson, but weak force interactions of a similar magnitude to a Z boson is likewise ruled out by direct DM detection searches, at least in the 1 GeV to 1000 GeV mass range that is usually assumed for a Z' boson, although like any hypothetical particle you can assign pretty much any properties to it to try to fit the data.

Axion-like particle (ALP) dark matter candidate properties are even more ill-defined, and while all are very light there are many, many orders of magnitude of parameter space open. Lots and lots of direct searches from ALP have come up empty, but most of the searches cover only tiny parts of the parameter space. ALPs are also ill motivated in the large part of the parameters space currently being proposed that have nothing to do with the original justification for them to cause the QCD force to have no CP violation.

At some point, ALP DM and effects of gravitons in a quantum gravity regime become hard to distinguish, so the search for ALPs if, in fact, DM effects are really gravitational, may be one of the longest lived DM candidates.