I Dark Matter and who will discover it first?

[infinitebubble]

While the subject has been talked about to death by many a researcher, who will discover the first dark matter scientific paper that will prove beyond theory that describes it in detail. The real discoverer will undoubtedly be the hero of physics, astrophysics, and cosmology and be awarded surely the Nobel Prize for science. Any notables that today seem on the cusp of it's discovery?

My takes:
Lisa Randall
Richard Massey
George Efstathiou

Among others...

 

[mfb]

The discoverers of dark matter particles will be groups of experimental physicists.
There are many viable theoretical models of dark matter, and we need experimental results to figure out what we have in nature.

Groups have a poor track record of getting Nobel Prizes. See the Higgs boson.

Zwicky, Oort and Kapteyn would be potential Nobel Prize candidates (as first scientists to find evidence of dark matter), but they are dead. Vera Rubin was a candidate for a long time, but died in 2016. Kent Ford is still alive (86) but I would be surprised if he gets the prize.

 

[MichaelMo]

Cusp of it's discovery? It's been more than 80 years since Fritz Zwicky first proposed the idea and the LHC just verified the stunning predictive accuracy of the standard particle physics model, so your optimism seems a tad premature. :)

 

[Stavros Kiri]

I hate to disappoint you (us), but as of now there is (almost?) zero experimental evidence of DM. LUX experiment, at its maximum sensitivity (for now), failed (last summer) to detect even one single particle of Dark Matter:
http://phys.org/news/2016-07-world-sensitive-dark-detector.html

I think there will be a new LUX (possibly with even higher sensitivity), and I am not aware of the progress on the subject ever since.
But what happens if they still discover nothing? What will be the fate of Dark Matter then? Experiment is the ultimate judge of theories ...

 

[Stavros Kiri]

I think there will be a new LUX (possibly with even higher sensitivity), and I am not aware of the progress on the subject ever since.

It was only last summer when the high resolution LUX experiment failed to detect WIMP's of dark matter. This year (last May) XENON1T beats LUX in sensitivity but still did not detect any dark matter candidate:

https://phys.org/news/2017-05-xenon1t-sensitive-detector-earth-wimp.html

For the results see directly the original paper (reports consistent with background only):

First Dark Matter Search Results from the XENON1T Experiment.
https://arxiv.org/abs/1705.06655

From what I heard, a new hope now could rely on the follow-up project of LUX, the LUX-ZEPLIN, with its colossal detector size (around 90 times more sensitive than LUX).
Failing of that also ("knock on wood" ... !?) however won't bode well for anyone getting a nobel prize (for Dark Matter), or for the future of Dark Matter itself! ...

I guess we'll find out.

 

[mfb]

The XENON1T result was based on a single month of data-taking, they'll improve that limit quickly.
LUX-ZEPLIN (2020+) and XENONnT (2019-2020+) will both improve it again. DARWIN aims for a start 2023, and it will either find dark matter or improve the exclusion limits to the neutrino background.
Currently the experiments double the sensitivity roughly every year. I wrote a bit more about the searches in this Insights article.

 

[stoomart]

Has there been any detection effort or serious research of anapole dark matter?

Anapole Dark Matter: https://arxiv.org/abs/1211.0503
Anapole Dark Matter at the LHC: https://arxiv.org/abs/1311.5630

 

[ohwilleke]

There is no evidence of dark matter particles that interact via any of the three Standard Model forces (electromagnetic, weak, strong) over a mass range that extends from at least 1 GeV to 1000 GeV based upon direct dark matter detection experiments and the LHC. Moreover, astronomy observations strongly disfavor heavier dark matter candidates. And, collisionless cold dark matter is also pretty strongly disfavored with a possible exception in the keV mass range.

There is a constant flood of new astronomy observations that continue to tighten (and indeed come close to overconstraining) the parameter space for dark matter, but we can be reasonably confident that direct detection of dark matter is not going to happen any time in the next thirty year or more, if ever. Dark matter makes neutrinos look like bulls in China shops.

 

[mfb]

There is a constant flood of new astronomy observations that continue to tighten (and indeed come close to overconstraining) the parameter space for dark matter, but we can be reasonably confident that direct detection of dark matter is not going to happen any time in the next thirty year or more, if ever.

What exactly rules out a possible discovery by XENON1T and its follow-up experiments?

 

[Stavros Kiri]

A)

but we can be reasonably confident that direct detection of dark matter is not going to happen any time in the next thirty year or more, if ever.

It is necessary for this (below) timetable etc. to be followed first, before anyone can conclude anything ... :

LUX-ZEPLIN (2020+) and XENONnT (2019-2020+) will both improve it again. DARWIN aims for a start 2023, and it will either find dark matter or improve the exclusion limits to the neutrino background.

Unless something else conclusive happens before then to prove, disprove or totally reject DM etc.

In the meantime, I'm anxious waiting for those experiments and results! ...

B)

Has there been any detection effort or serious research of anapole dark matter?

Anapole Dark Matter: https://arxiv.org/abs/1211.0503
Anapole Dark Matter at the LHC: https://arxiv.org/abs/1311.5630

I am not aware, ... other than what you cited.

 

[ohwilleke]

What exactly rules out a possible discovery by XENON1T and its follow-up experiments?

Some of sub-GeV mass range is also excluded by direct searches at the LHC. The latest LHC results even strictly limit Higgs channel dark matter candidates.

Equally important, if the kind of dark matter that these direct dark matter detection experiments are looking for exists, it would behave in a very particular way that would be reflected in its behavior that can be indirectly observed with astronomy observations such as rotation curve and lensing measurements of inferred dark matter halos. The behavior of the kind of dark matter sought is also the single most well modeled scenario in N-body simulations of dark matter.

For example, generically, dark matter of the kind that could could be found by XENO1T and its follow-up experiments would generate the wrong shaped/wrong density distribution halos (something that baryonic feedback mediated only by gravity and weaker than neutrino weak force interactions can't alleviate), would not be able to reconcile measurements based upon rotation curves and those based upon lensing, would not track baryonic matter distributions as tightly as observation indicates, would not generate particle velocities sufficient to give rise to the number of observed high velocity galactic cluster systems of which the Bullet Cluster is an example, and would generate more small scale structure (such as satellite galaxies) than is observed by astronomers.

Some of these problems are summarized in a literature review supported by references from this preprint (references fully described in end notes in the original, paragraph breaks inserted for ease of reading in this non-typeset format):

At the galactic scale masses of M < 10¹¹⁻¹²M , the predicted WIMP/ΛCDM dark matter halos are much more numerous than those detected and show very different structural properties with respect to those inferred by the internal motions of galaxies (e.g. see Salucci, F.-Martins & Lapi (2011)). The questioning issues for the WIMP particle are well known as the “missing satellites” ( Klypin et al. (1999)), the “too big too fail” (Boylan-Kolchin et al. (2011)) and the lack of a cuspy central density profiles in the DM halos (Gentile et al. (2004); Spano et al. (2008); Oh et al. (2011) and reference therein).

There are proposals in which astrophysical processes could modify the predictions of the N-body ΛCDM models and the related density profiles to fit the observations (e.g. Vogelsberger et al. (2014); Pontzen & Governato (2012); Di Cintio et al. (2014); Read, Agertz, & Collins (2016)). However, this modelizations are growing in number and in diversity (Karukes & Salucci (2016)) and the cores formation via hypothetical strong baryonic feedbacks requires ad hoc fine tuning.

Let us also remind that WIMP particles have not convincingly been detected in underground experiments (see e.g. Freese (2017)) and they have not emerged even in the most energetic LHC proton-proton collisions (e.g.CMS collaboration (2017)).

Finally, the X and gamma ray radiation coming from annihilating WIMP particles at the center of our and nearby galaxies has not unambiguously been detected ( Freese (2017), e.g. Albert et al. (2016); Lovell et al. (2016)). Thus, to claim that ΛCDM is not anymore the forefront cosmological scenario for dark matter will bring no surprise.

Recent alternative scenarios for dark matter point to a sort of significant self-interactions between the dark particles which seems suitable to explain the observational evidence which has created the ΛCDM crisis. Among those, the Warm Dark Matter, the axion as a BoseEinstein condensate and the self-interacting massive particles scenario (e.g. Freese (2017); Krishna et al. (2017); Suarez et al. (2014); de Vega, Salucci, & Sanchez (2014)) are the most promising. Their common characteristic is that, at galactic scales, dark matter stops to be collisionless and it starts to behave in a way which could make it compatible with observations. However, also these scenarios hardly explain the fact that we continue to find that in galaxies, dark and luminous matter are extremely well correlated (e.g. Gentile et al. (2009)). . . . In fact, the dark-luminous coupling that emerge in spirals is so intricate that it is extremely difficult to frame it in a scenario in which the dark and the luminous galactic components are completely separated but through their gravitational interaction.

(At the large scale structure/CMB/lamda CDM scale, the Standard Model of Cosmology is insensitive to the details of dark matter particle properties from wark dark matter in the roughly keV scale all of the way up to brown dwarf sized MACHOs and stellar black holes, so long as it is very nearly collisionless.)

The noise created by the neutrino background which currently can't be effectively filtered out, undermines the methodology of these experiments long before they have enough resolution to detect warm dark matter that might behave differently in the respects described above.

 

[Stavros Kiri]

While looking for Dark Matter on earth, in the meantime, a group of astronomers have discovered a galaxy with no dark matter at all! ... Or have they?
https://physicsworld.com/a/galaxy-devoid-of-dark-matter-puzzles-astronomers/

However, note that that can be proof by itself that DM exists ... , providing the data is correct and no other plausible explanation can be found ...

 

[phinds]

While looking for Dark Matter on earth, in the meantime, a group of astronomers have discovered a galaxy with no dark matter at all! ... Or have they?
https://physicsworld.com/a/galaxy-devoid-of-dark-matter-puzzles-astronomers/

However, note that that can be proof by itself that DM exists ... , providing the data is correct and no other plausible explanation can be found ...

There's already a thread on this:
https://www.physicsforums.com/threads/galaxy-with-no-dark-matter-ngc1052-df2.943345/

 

[eachus]

Sigh! I'm reminded of the drunk searching for his keys under a streetlight. He hadn't dropped them there, but the light was much better.

How much dark matter is in the solar system? To make the question specific, inside the orbit of Neptune.

There may be some, but on the order of a few kilos. How do we know that? NASA, ESA and others have been sending spacecraft all around the solar system--and beyond. If there was any significant amount of dark matter around, the trajectories of the spacecraft would have been changed. Yes, the acceleration might be on the order of a nanometer per second squared--but such effects on spaceprobes have been studied. Remember the Pioneer anomaly, caused by differential heat radiation from the RTG? There might be dark matter trapped by gravity in the center of planets or the sun, but even that is unlikely. Models of the interior of the Earth from seismic waves don't leave much wiggle room.

Let me propose a dark matter particle that has a mass on the order of neutrinos, and interacts with photons and other matter about as rarely. What happens? The rate of interactions and the relative masses mean that it wouldn't show up by fuzzing light from other stars and galaxies. It might have that effect on radio waves, but the expansion of the universe means that radio waves from far away arrive at Earth after being red shifted. So only the interaction during the last few billion years would be noticeable. ;-) Around galaxies and galaxy clusters, there should be a point where average interactions with photons (and neutrinos!) is balanced by the gravity from the galaxy or cluster.

Don't use Occam's Razor to conclude that okay, dark matter is made of neutrinos. Cosmology calls for a lot more DM than neutrinos in the early universe by mass. My best guess would be a particle in the kev range, emitted only during high-energy particle interactions. It might not be the right answer, but I know that the right answer will not be found by looking under the streetlight.

 

[mfb]

There may be some, but on the order of a few kilos. How do we know that? NASA, ESA and others have been sending spacecraft all around the solar system--and beyond. If there was any significant amount of dark matter around, the trajectories of the spacecraft would have been changed.

The expected amount of dark matter is comparable to a small asteroid. Much more than a few kilograms, but still way too small to notice it with spacecraft . If spacecraft would have found a deviation it would have indicated that our dark matter models are wrong.

Models of the interior of the Earth from seismic waves don't leave much wiggle room.

Seismic waves don't constrain the amount of dark matter inside Earth in any relevant way.

Neutrinos can be considered a part of dark matter, but they cannot clump on the scale of galaxies, nothing like them can be a large part of dark matter. Axions are a possible model with small mass.

It might have that effect on radio waves

In that case it wouldn't be dark matter.

So only the interaction during the last few billion years would be noticeable.

You can't have an interaction that is selective to wavelengths. In addition, radio waves have been around the whole time.

It might not be the right answer, but I know that the right answer will not be found by looking under the streetlight.

As a first step, you should learn how the key we are searching looks like.

 

[ohwilleke]

The expected amount of dark matter is comparable to a small asteroid. Much more than a few kilograms, but still way too small to notice it with spacecraft . If spacecraft would have found a deviation it would have indicated that our dark matter models are wrong.

Just to embellish slightly on this part of your answer, not only is it comparable to a small asteroid (which as you note, still isn't much), it would be more of less evenly dispersed through the entire volume of space in that part of the the solar system. So, at a solar system level, there would be observable effects only to the extent that there was inhomgenity in the dark matter distribution. The bottom line is the same: it is way too small to notice it with space craft. But, because it would be so broadly and evenly dispersed, it would be multiple orders of magnitude harder to notice than a simple single small asteroid would be.

 

[Chronos]

If the dark matter density profile of the solar system mimics that believed of galaxies, it may help explain why direct detection has proven so challenging. This does not, however, necessarily spell doom for the current generation of experiments.

 

[mfb]

If the dark matter density profile of the solar system mimics that believed of galaxies

It does not. Dark matter doesn't clump on scales that small - that would need a strong interaction that it cannot have.

 

[Chronos]

I would not call ~0.4 Gev/cm³ [the estimated DM density at the suns vicinity in the MW per https://arxiv.org/abs/1212.3670 ] very clumpy. That works out to about 8 x 10^-25 gm/cm³ on average. Assuming the density peaks at the sun similar to the DM density at the MW core and falls off sufficient to meet this calculated average for the volume encompassed by the Oort cloud, looks fairly plausible to me.

 

[mfb]

Assuming the density peaks at the sun similar to the DM density at the MW core

It does not. That's exactly what my post said.
"Clumping" is a statement about the distribution, the average density somewhere has nothing to do with it. The density is very uniform at the scale of the solar system.

 

[Chronos]

Permit me to clariy, While the average DM density is indeed irrelevant. DM density peaks [note the caveat: assuming they exist] may be within detection limits of the latest generation of DM experiments

 

[mfb]

To get strong localized peaks you need some relevant interaction apart from gravity - but such an interaction would also make a disk out of dark matter, contrary to the halo we have.

 

[Chronos]

Dark matter density can be more complicated than you are apparently suggesting, as discussed here: https://arxiv.org/abs/0810.0277,
Evolution of the Dark Matter Phase-Space Density Distributions of LCDM Halos.

 

[mfb]

Where exactly are they discussing scales as small as planetary systems?

 

[Chronos]

Understood and agreed. This, https://arxiv.org/abs/0810.0277. is not the ideal reference for discussion of local DM density. While It does capture some of the nuances of small scale DM density variation, the smallest scales specifically addressed are of MW size order, not solar system size subhalos. To that end, I suggest this one as more suitable; https://arxiv.org/abs/1404.1938, The Local Dark Matter Density. I feel it offers real hope the current generation of direct DM detection experiments have potential to succeed - depending, of course, upon how strict a standard of proof desired. For those with 'pin it to a display board and hang in a museum' mentality, a little LHC magic is probably needed. Just a brief comment here. Since a fairly popular belief is that DM is born cold, LHC may be a long shot. For the less demanding, even GAIA may be persuasive; https://arxiv.org/abs/1506.00384, The difficulty of measuring the local dark matter density.

 

[Monsterboy]

Does the "Dark matter might be primordial black holes" theory have any merit ?

https://www.space.com/33122-dark-matter-black-hole-connection.html

When the researchers removed all of the light from the known galaxies throughout the universe, they could still detect excess light — the background glow from the first sources to illuminate the universe more than 13 billion years ago.

Then, in 2013, Kashlinsky and his colleagues used NASA's Chandra X-ray Observatory to explore the background glow in a different part of the electromagnetic spectrum: X-rays. To their surprise, the patterns within the infrared background perfectly matched the patterns within the X-ray background.

" And the only sources that would be able to produce this in both infrared and X-rays are black holes," Kashlinsky said. "It never crossed my mind at that time that these could be primordial black holes."

Is this about accretion disks ?