Towards a purely gravitational effective theory of dark matter

[mitchell porter]

TL;DR Summary

Constructing a purely gravitational, nonlocal action that reproduces CDM cosmology

"The Price of Abandoning Dark Matter Is Nonlocality" (Deffayet, Woodard)

written in response to

"What is the price of abandoning dark matter? Cosmological constraints on alternative gravity theories" (Pardo, Spergel)

In a nutshell, as explained after equation 34, by adding a nonlocal self-interaction to the metric, they can reproduce the effects normally attributed to CDM.

From the conclusion:

We stress that there can be no doubt about this model reproducing all the successes of CDM in cosmology. Those successes include the anisotropies of the cosmic microwave background, baryon acoustic oscillations, and linearized structure formation. All of this must come out right because this model was constructed by using the separate conservation of the CDM stress tensor to express it as a nonlocal functional of the metric. The only way this model can be falsified is by showing that CDM interacts with fields other than gravity, the evidence for which is weak. This model should put to rest the frequent claims that no modified gravity theory can supplant dark matter. It also demonstrates that the answer to the question of Pardo and Spergel about the price of abandoning dark matter: the price is nonlocality...

One thing our model does not do is to agree with the nonlocal extension of MOND [this refers to earlier work by the authors] which was constructed to reproduce the baryonic Tully-Fisher relation, with sufficient weak lensing, in gravitationally bound structure... It would be desirable to have a single formalism which connects both regimes.

It would also be desirable to derive these nonlocal models from fundamental theory. We believe they might arise from resumming the secular logarithms that are induced by loops of inflationary gravitons and which must eventually become nonperturbatively large during a prolonged period of inflation

edit: 2021 talk by Woodard

 

[kodama]

TL;DR Summary: Constructing a purely gravitational, nonlocal action that reproduces CDM cosmology

In a nutshell, as explained after equation 34, by adding a nonlocal self-interaction to the metric, they can reproduce the effects normally attributed to CDM.

is adding a nonlocal self-interaction to the metric similar to Deur claims of self-interaction to the metric?

 

[ohwilleke]

TL;DR Summary: Constructing a purely gravitational, nonlocal action that reproduces CDM cosmology

"The Price of Abandoning Dark Matter Is Nonlocality" (Deffayet, Woodard)

written in response to

"What is the price of abandoning dark matter? Cosmological constraints on alternative gravity theories" (Pardo, Spergel)

In a nutshell, as explained after equation 34, by adding a nonlocal self-interaction to the metric, they can reproduce the effects normally attributed to CDM.

From the conclusion:

edit: 2021 talk by Woodard

FWIW, while their model is very interesting, their implication that non-local gravity is the only gravitational approach that can give rise to the observed phenomena often attributed to dark matter is a claim that isn't supported by their paper in any rigorous way. A slightly different spin on their result would have been preferable.

 

[wumbo]

Abandoning locality is certainly an approach. I think some people forget that the general relativity is highly constrained by the equivalence principle and is mostly a consequence of that + the postulates of special relativity. So which postulate is broken and what evidence is there for it?

Unless they proved non-locality is a necessary aspect, which IIRC it isn't, I think it's safe to discount such approaches without a very good reason.

 

[ohwilleke]

Abandoning locality is certainly an approach.

FWIW, there are 83 non-local gravity papers on arXiv. The most recent was posted in April 2024, the oldest dates to September 2008.

One of the older ones, F. Darabi, "Dark matter, MOND or non-local gravity?" (July 2009) is facially addressing just the issue raised by wumbo.

 

[Mordred]

Although the approach is interesting I noticed they never looked into early scale structure formation which is attributed to the DM term. If I recall this is also a problem MOND never really addressed

 

[Mordred]

I wonder how the first article would weigh against Press-Schechter mass distributions as this method is often used to calculate the dark halo and galaxy distributions

Example here
https://www.roe.ac.uk/japwww/teaching/cos5_0910/cos5_0910_part5.pdf

 

[ohwilleke]

Although the approach is interesting I noticed they never looked into early scale structure formation which is attributed to the DM term. If I recall this is also a problem MOND never really addressed

Early structure formation has been addressed in MOND. Generically, MOND gives rise to structure formation more rapidly than particle DM. This is why the impossible early galaxies problem disfavors DM v. MOND, and for that matter, most modified gravity theories. I'll see if I can find some of the citations to papers on point.

 

[Mordred]

Please do as the MOND variations I am familiar with didn't address that so I would be interested if you can find some good citations. Complexity of mathematics isn't an issue.

 

[ohwilleke]

Please do as the MOND variations I am familiar with didn't address that so I would be interested if you can find some good citations. Complexity of mathematics isn't an issue.

Not a problem. I have them buried away in old blog posts and a somewhat elaborate set of folders with bookmarks for journal articles. It just takes a while to find them sometimes. It's probably been a year and a half since I looked at the question, and I add maybe twenty or thirty bookmarks a week.

 

[Mordred]

Sounds like my terabyte drive of pdfs and storage closet of textbooks lol. I too collect literature

 

[ohwilleke]

Why look for musty old stuff when I can give you something hot off the presses?

Galaxies in the early universe appear to have grown too big too fast, assembling into massive, monolithic objects more rapidly than anticipated in the hierarchical ΛCDM structure formation paradigm. The available data are consistent with there being a population of massive galaxies that form early (z≳10) and follow an approximately exponential star formation history with a short (≲1 Gyr) e-folding timescale on the way to becoming massive (M∗≈10¹¹M⊙) galaxies by z=0, consistent with the traditional picture for the evolution of giant elliptical galaxies. Observations of the kinematics of spiral galaxies as a function of redshift similarly show that massive disks and their scaling relations were in place at early times, indicating a genuine effect in mass that cannot be explained as a quirk of luminosity evolution. That massive galaxies could form by z=10 was explicitly predicted in advance by MOND. We discuss some further predictions of MOND, such as the early emergence of clusters of galaxies and the cosmic web.

Stacy S. McGaugh, James M. Schombert, Federico Lelli, Jay Franck, "Accelerated Structure Formation: the Early Emergence of Massive Galaxies and Clusters of Galaxies" arXiv:2406.17930 (June 25, 2024) (submitted to Apj).

 

[Mordred]

Why look for musty old stuff when I can give you something hot off the presses ?

Simple answer comparisons. As well as examining the different methodologies.

Thanks for the link I will examine it.

Edit : The portion of that paper referring to Jeans scale though applicable is a rather old method. There are more modern methods in regards to early inhomogenous mass distributions. Hopefully the paper details the modern methods used by LCDM.
It's late atm will have to examine it closer later on

 

[Mordred]

Ah found the methodology I was hoping they applied for DM halos (Press-Schechter formalism). Missed that detail last night. Decent paper thanks again.
Just a side note we still don't have a clear understanding of how early DM forms so this is also a factor beyond luminosity factors.