Did the LUX Dark Matter Experiment Fail to Detect Dark Matter?

[ProfChuck]

An important question regarding the properties of dark matter is "Does DM introduce Faraday rotation to signals that pass through it?". While by definition DM is not directly observable as a luminous source it may introduce artifacts to signals originating from more distant objects. These artifacts could include time dispersion and birefringence. A measure of such phenomena in the region of suspected DM has been suggested by Susan Gardner of the University of Kentucky.

(https://www.researchgate.net/publication/23417584_Shedding_Light_on_Dark_Matter_A_Faraday_Rotation_Experiment_to_Limit_a_Dark_Magnetic_Moment )

The results of these observations could shed considerable "light" on the dark matter question. Most importantly is DM exotic matter or is it just ordinary matter that is too cold to be detected directly by conventional astronomical methods and instruments.

 

[jerromyjon]

Your comment seems to be about dark energy (acceleration of expansion)

Yes. I was asking if the analogy makes sense: "dark energy is to expansion as dark matter is to mass"?

 

[Vanadium 50]

Most importantly is DM exotic matter or is it just ordinary matter that is too cold to be detected directly by conventional astronomical methods and instruments.

It is not ordinary matter.

• It is too transparent. This much ordinary matter would be visible as gas or dust.
• Big-bang nucleosynthesis limits the amount of matter to be atomic to ~10% of the total matter
• CMBR limits are similar
• Microlensing shows no clumping of the sort you would expect from atomic matter
• The Bullet Cluster shows a component of matter that interacts much less strongly than ordinary atomic matter

 

[jerromyjon]

The main problem though seems to be that in order for such a thing to form, we could expect abundances of isotopes in normal matter to be different to what they actually are.

My "guess" is that depends where you look, take the center of the milky way for example... we need a more "dynamic" inventory.

 

[RUTA]

We believe DM and DE are both manifestations of small geometric perturbations from idealized GR solutions. Here is a quick overview of our idea https://arxiv.org/abs/1605.09229 which will appear in IJMPD as an Honorable Mention in this year's GRF essay contest. We have redone the DM fits in this paper using the exact same fitting technique we used for DE (as shown in this paper), i.e., the fitting function uses explicitly the metric perturbation $h_{\alpha \beta}$. That will appear in a longer paper which will include a fit of the Planck CMB power anisotropy data (also using the same fitting technique). The bottom line in our approach is that mass is not an intrinsic property of matter, it is a relational property and can have different values in different contexts. This is already true in GR, e.g., an FRW dust ball interior to a Schwarzschild vacuum where M of the Schwarzschild metric is equal to, less than, or greater than the FRW proper mass depending on the FRW spatial geometry. So the matter of the FRW dust ball has two different values of mass, depending on the context.

 

[PeterDonis]

an FRW dust ball interior to a Schwarzschild vacuum where M of the Schwarzschild metric is equal to, less than, or greater than the FRW proper mass depending on the FRW spatial geometry.

How is the "FRW proper mass" defined? (I see a brief statement that might be relevant in the paper you linked to, but it doesn't give any details; it just gives two references, one of which is Wald's textbook, but with no chapter/page. A more specific reference to the chapter/page in Wald where this is discussed would be helpful.)

 

[RUTA]

How is the "FRW proper mass" defined? (I see a brief statement that might be relevant in the paper you linked to, but it doesn't give any details; it just gives two references, one of which is Wald's textbook, but with no chapter/page. A more specific reference to the chapter/page in Wald where this is discussed would be helpful.)

Proper mass is simply the mass obtained by integrating the dust density in the FRW ball, i.e., cosmology proper mass measured by the comoving observers of a dust-filled universe. The "dynamic mass" would be the mass obtained by observers outside the ball using M of the Schwarzschild geometry. I just ck'd and the arXiv paper has p. 126 for the Wald reference. The AJP paper is too old for the arXiv, but I can send a copy when I get to the office tomorrow if you'd like.

 

[PeterDonis]

Proper mass is simply the mass obtained by integrating the dust density in the FRW ball, i.e., cosmology proper mass measured by the comoving observers of a dust-filled universe.

Integrating with what measure?

 

[RUTA]

Integrating with what measure?

The FRW metric interior to the ball. Here is a link to the paper:
http://users.etown.edu/s/STUCKEYM/AJP1994.pdf

 

[phinds]

Yes. I was asking if the analogy makes sense: "dark energy is to expansion as dark matter is to mass"?

I doubt that question even makes sense. Would it even have occurred to you to ask it if what we call dark energy were called vacuum energy and dark matter was called Zwicky matter. The only thing they really have in common is our use of the word dark in their names.

 

[PeterDonis]

Here is a link to the paper

Thanks! I'll take a look.

 

[jerromyjon]

The only thing they really have in common is our use of the word dark in their names.

And that they are both undetectable in local space as normal matter and energy, they are more similar to each other than to anything else in physics. That could certainly be a coincidence but it could also be a connection. I'm not just going to flip a coin and see which way it lands, I'm keeping an open mind. =D

 

[mfb]

Electron neutrinos and muon neutrinos are much more similar than dark matter and dark energy.

I would argue that even neutral gas is more similar to dark matter than dark energy is.

 

[Vanadium 50]

dark matter was called Zwicky matter.

Please. Zwicky-Rubin matter.

 

[phinds]

Please. Zwicky-Rubin matter.

My point was simply "not 'dark' matter"

 

[jerromyjon]

I would argue that even neutral gas is more similar to dark matter than dark energy is.

Yes, I agree with you from a physics viewpoint.

My point was simply "not 'dark' matter"

Ignore the names of the phenomena and could you at least see that I have a sensible question at the heart of it all. Dark matter makes the stars in galaxies and clusters move differently than general relativity would predict. Dark energy makes all stars in galaxies and clusters (which are further apart and not bound) accelerate away from each other (at a lessening rate). They seem like 2 sides of the same galactic "coin" to me.

I do have a tendency to over-simplify things but there is a method to my madness and I do understand the finer implications of the details, even if I don't possesses the skills to quantify my thoughts, yet.

 

[PeterDonis]

Dark matter makes the stars in galaxies and clusters move differently than general relativity would predict.

No, dark matter makes the stars in galaxies and clusters move differently than they would move if the dark matter were not there. But the motion including the effect of the dark matter is perfectly consistent with GR, and the effect of dark matter, gravitationally, is the same as the effect of ordinary matter.

 

[mfb]

Stuff in galaxies and clusters would also move differently if regular matter would not be there. Even worse: we would not even have stars moving around.

 

[phinds]

Yes, I agree with you from a physics viewpoint.
And what other point of view would you like to bring to bear on the question?

Ignore the names of the phenomena and could you at least see that I have a sensible question at the heart of it all.

I disagree. Others have already pointed out the reasons.

 

[jerromyjon]

No, dark matter makes the stars in galaxies and clusters move differently than they would move if the dark matter were not there. But the motion including the effect of the dark matter is perfectly consistent with GR, and the effect of dark matter, gravitationally, is the same as the effect of ordinary matter.

So there is just random stuff we can't see, mixed randomly with the stuff we can see. Alright then. Thanks.

 

[Drakkith]

So there is just random stuff we can't see, mixed randomly with the stuff we can see. Alright then. Thanks.

Not quite random, no. It seems to be concentrated into roughly spherical "halos" around most galaxies and into other areas where a non-interacting type of matter would be expected to concentrate at. Offset from the point of collision between galaxies, for example, since the normal matter slows down during the collision but the dark matter passes right through and continues on.

 

[Laurie K]

Not quite random, no. It seems to be concentrated into roughly spherical "halos" around most galaxies and into other areas where a non-interacting type of matter would be expected to concentrate at. Offset from the point of collision between galaxies, for example, since the normal matter slows down during the collision but the dark matter passes right through and continues on.

We also get total rotational matter = dark matter + visible matter = visible matter x $$2 \pi$$ +/- 3%.

This $$2 \pi$$ is just the difference between the calculated rest mass, attributed to our astronomical observations and the sum (relativistic) mass, used in our Lambda CDM calculations which gives us dark matter.

 

[phinds]

We also get total rotational matter = dark matter + visible matter = visible matter x $$2 \pi$$ +/- 3%.

This $$2 \pi$$ is just the difference between the calculated rest mass, attributed to our astronomical observations and the sum (relativistic) mass, used in our Lambda CDM calculations which gives us dark matter.

Huh? "Relativistic mass" as related to dark matter? Clearly one of us is misunderstanding something. And what does pi have to do with dark matter?

 

[mfb]

We also get total rotational matter = dark matter + visible matter = visible matter x $$2 \pi$$ +/- 3%.

This $$2 \pi$$ is just the difference between the calculated rest mass, attributed to our astronomical observations and the sum (relativistic) mass, used in our Lambda CDM calculations which gives us dark matter.

The fraction of visible matter relative to total matter varies between galaxies by much more than 3%, such an equation does not make sense. The overall dark matter density is not known more precisely than 4%, so that doesn't work either.

The concept of relativistic mass is not used any more, but the difference between this and the visible mass is negligible (about 1 part in a million difference).

To summarize, your post doesn't make sense at all.

 

[Laurie K]

The fraction of visible matter relative to total matter varies between galaxies by much more than 3%, such an equation does not make sense.

In a universal sum calculation, like the percentages of dark matter and visible matter given by Planck 2013 data, it does make sense. In the Planck 2015 revision the total percentages included dark energy but the ratio shown between dark matter% and visible matter% remain the same.

 

[mfb]

You can calculate the ratio if you take the average densities in the observable universe, but per galaxy the numbers vary much more.

The 2015 results include Ωc = .258 with 2% uncertainty and Ωb = .048 with 3% uncertainty, the ratio is 5.38 with about 4% uncertainty.

 

[1oldman2]

While reading, http://www.nasa.gov/feature/goddard/2016/nasas-fermi-mission-expands-its-search-for-dark-matter I was linked to, https://www6.slac.stanford.edu/news...s-explore-new-ways-searching-dark-matter.aspx as well as, http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.161101 This led me to, http://www.symmetrymagazine.org/article/dark-matter-hopes-dwindle-with-x-ray-signal which reminded me what a loss Hitomi was to the field of Astronomy, the bright side is NASA and JAXA are considering a replacement in the future.

 

[jerromyjon]

what a loss Hitomi was to the field of Astronomy

It did rule out the sterile neutrino possibility at 3.5keV even though it was filtered below 5keV? Would the expected intensity have overpowered the filter? I don't quite understand that.

 

[1oldman2]

The filter being in place during the survey, I'm wondering if that was done intentionally or by accident. A 5kv filter while searching for a 3.5kv signal seems strange, hoping someone comments that. I've read the article several times and while it seems to rule out the decaying dark matter aspect it does leave an unanswered question, namely what was the "anomalously strong signal" detected in other studies.

From, http://www.symmetrymagazine.org/article/sterile-neutrinos-in-trouble
With their new result, IceCube scientists are fairly certain the most
popular explanation for the anomaly is incorrect. In a paper published in
Physical Review Letters, they report that after searching for the
predicted form of the stealthy particle, they excluded its existence at
approximately the 99 percent confidence level.

"The sterile neutrino would’ve been a profound discovery," says
physicist Ben Jones of the University of Texas, Arlington, who worked
on the IceCube analysis. "It would really have been the first particle
discovered beyond the Standard Model of particle physics."

This doesn’t mean they can completely rule out the existence of
low-mass sterile neutrinos, Jones says. "But it’s also true to say that the
likelihood that a sterile neutrino exists is now the lowest it has ever been
before."

The search for the sterile neutrino continues. Kopp says the planned
Short Baseline Neutrino program at Fermilab will be perfectly calibrated
to investigate the remaining mass region most likely to hold low-mass
sterile neutrinos, if they do exist.

In the end, if these experiments throw cold water on the low-mass
sterile neutrino theory, they will still have another question to answer: If
sterile neutrinos did not cause the anomaly at Los Alamos, what did?

The new data were collected during Hitomi’s first month in space, just
before the satellite was lost due to a series of malfunctions.
Unfortunately during that time, the SXS was still covered with a
protective filter, which absorbed most of the X-ray photons with
energies below 5 keV.

"This limited our ability to take enough data of the 3.5-keV line," Werner
says. "The signal might very well still exist at the much lower flux level
observed in the stacked data."

Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its
X-ray signal is not anomalously strong. A signal 30 times stronger than
expected would have made it through the filter.

 

[Laurie K]

The 2015 results include Ωc = .258 with 2% uncertainty and Ωb = .048 with 3% uncertainty, the ratio is 5.38 with about 4% uncertainty.

The 2013 Planck data from the wikipedia page is quoted as 4.82% +/- 0.05% for ordinary matter and 25.8% +/- 0.4% for dark matter so (25.8 + 4.82) = 4.82 * 2 * Pi +/- 1%.
https://en.wikipedia.org/wiki/Planck_( spacecraft )#2013_data_release

According to the team, the Universe is 13.798±0.037 billion years old, and contains 4.82±0.05% ordinary matter, 25.8±0.4% dark matter and 69±1% dark energy.

 

[phinds]

... so (25.8 + 4.82) = 4.82 * 2 * Pi +/- 1%.

So apparently you continue to contend that this is something other than just numerology.

 

[mfb]

Ah, you divide the sum by the visible matter component. Anyway, there is nothing special about 2 pi. If you think otherwise, please give a reference to a peer-reviewed publication discussing this.

 

[jerromyjon]

but per galaxy the numbers vary much more.

What about closer to home, is there evidence of dark matter in our solar system? I haven't heard anything recently about the anomalous movements of bodies in our solar system which could be attributed to an unseen planet or planets, could dark matter be less than the amount of visible matter, locally, or does it always dominate the total mass?

 

[mfb]

What about closer to home, is there evidence of dark matter in our solar system?

No, and it is not expected. The amount of dark matter in our solar system is tiny, simply because our solar system is small compared to galactic scales. The overall dark matter mass should be similar to the mass of a small asteroid.

 

[jerromyjon]

It seems to be concentrated into roughly spherical "halos" around most galaxies

So that just tells me that it has little effect in the middle of a galaxy where it would have a symmetrical influence, but as you look further from center it has more of an impact on visible stars, making them rotate around the center faster than expected. Are there any examples of galaxies where it has more distinguished effect? I'm just looking for extreme examples of how it makes visible matter behave or examples of galaxies without much of it.