Dark matter is running out of places to hide!

[Adrian59]

TL;DR Summary

With the release of the Lux Zeplin detector results this month coupled with the culmination of run 2 at CERN (another no show for dark matter) where next for dark matter?

The second half of 2024 has seen the results from 3 years of data from the Lux Zeplin experiment in South Dakota, USA. Despite their attempts to put a positive spin on this, the bottom line is - no dark matter.

Just three months before that the ATLAS experiment from CERN in Geneva, Switzerland concluded that there was no dark matter signal in their run 2 from 2015 - 2018, after reaching energies of 13 TeV.

Some of you may, also, recall that a couple of years ago MicroBoone said goodbye to sterile neutrinos!

 

[Vanadium 50]

Despite their attempts to put a positive spin on this, the bottom line is - no dark matter.

That seems like an odd complaint. Would you have preferred they lied and said there was? They saw what they saw.

Further, this is not an exhaustive list of where DM might be found. Suppose it's axions. LZ and the LHC would see nothing.

 

[Adrian59]

That seems like an odd complaint. Would you have preferred they lied and said there was? They saw what they saw

Of course not, but that doesn't alter anything, still no dark matter. Now you mention axions, has anyone proved strong CP violation because as far as I can see axions are a hypothetical fix to a hypothetical problem.

Further, this is not an exhaustive list of where DM might be found. Suppose it's axions. LZ and the LHC would see nothing

Well the theoretical space on the cross section versus mass graph doesn't have much left for any dark matter candidate whatever you call it. There seems to be a trend to give another name to a dark matter candidate and pretend that we haven't looked for it because it has a new name, but surely this is just semantics.

 

[PeroK]

If we knew there was no dark matter, we would stop looking for it. But, we don't know, so the search goes on. It might be there.

To stop searching would be unscientific.

 

[Orodruin]

Now you mention axions, has anyone proved strong CP violation because as far as I can see axions are a hypothetical fix to a hypothetical problem.

No, but that’s the point. It is exactly the absence of CP violation in the strong sector that motivates the original axions. That they provide a dark matter candidate was a nice bonus. But regardless of whether or not axions solve the strong CP problem (which is a very real problem for the axionless theory), you can always implement a dark matter candidate with similar properties - so called axion-like particles (ALPs). Those would not have been seen in the searches you mention but are very much datk matter candidates.

There are other candidates as well that would not show up in current experiments. We have barely scratched the surface of what is possible so to declare that the window is closing is highly misleading.

Well the theoretical space on the cross section versus mass graph doesn't have much left for any dark matter candidate whatever you call it.

That is simply false. In particular models with particular assumptions and particular production mechanisms perhaps, but in general nowhere close to true.

It should also be noted that many parameter space scans have a nasty tendency to produce samples which are predominantly close to current bounds when you look at them in log scale (as is often done in cross section and mass). This can create a false sense that lowering the cross section bound by an order of magnitude will rule out the model, which is not generally correct. Only a result of how the parameter space was scanned.

There seems to be a trend to give another name to a dark matter candidate and pretend that we haven't looked for it because it has a new name, but surely this is just semantics.

No, this is wrong and a misrepresentation of what is going on. Candidates with different names are fundamentally different in general with widely varying mass, cross sections, production mechanism, and other physical properties. It is definitely not just semantics.

 

[Orodruin]

Some of you may, also, recall that a couple of years ago MicroBoone said goodbye to sterile neutrinos!

This is also a misrepresentation by the way. They ruled out sterile neutrinos as the cause for the LSND anomaly. That is not the same thing as ruling out sterile neutrinos across the board. In particular, the type of sterile neutrinos that are often considered as a dark matter candidate live in a very different part of parameter space. They would be way to heavy and with way too small mixing with the standard neutrinos to show up at MicroBooNE.

 

[Adrian59]

If we knew there was no dark matter, we would stop looking for it. But, we don't know, so the search goes on. It might be there.

To stop searching would be unscientific.

That is true up to a point. However, as the great philosopher of science, Karl Popper said in his book 'The Logic of Scientific Discovery' (Ref. Popper, K. (1959) though my copy is published by Routledge, New York) 'no conclusive disproof of a theory can ever be produced'. So where do we draw the line? I would suggest when there are better alternatives which there are now such alternatives, and here I completely exclude all modified gravity theories.

 

[Orodruin]

I would suggest when there are better alternatives which there are now such alternatives, and here I completely exclude all modified gravity theories.

The scientific community does not seem to agree with you here. Alternatives (real alternatives, and I would point out that you have mentioned none except modified gravity, which you also said you exclude) are of course also worth pursuing, but dark matter remains the leading candidate.

 

[PeterDonis]

I would suggest when there are better alternatives which there are now such alternatives

Which ones? Please give specific references.

 

[Vanadium 50]

Gravitational acceleration beyond what is expected from visible matter is an observed fact (with multiple lines of evidence). If you exclude modified gravity as an explanation, you are arguing for dark matter.

 

[weirdoguy]

I would suggest when there are better alternatives

You started a thread with bunch of statements thate were not true/misinterpretation made by you. Why should anyone listen to your suggestions, if you don't get the facts right? You have a premise, you don't like dark matter, but it seems that it leads you astray.

 

[Adrian59]

This is also a misrepresentation by the way. They ruled out sterile neutrinos as the cause for the LSND anomaly. That is not the same thing as ruling out sterile neutrinos across the board. In particular, the type of sterile neutrinos that are often considered as a dark matter candidate live in a very different part of parameter space. They would be way to heavy and with way too small mixing with the standard neutrinos to show up at MicroBooNE.

Yes, but the LSND and MiniBoone anomalies were attributed to the possibility of sterile neutrinos (I have rechecked the original papers). So the MicroBoone results by ruling this out as an explanation, severely curtailed or even removed the evidence for sterile neutrinos. Unless there is another experiment that has found evidence for sterile neutrinos, they are off the agenda.

 

[Adrian59]

You started a thread with bunch of statements thate were not true/misinterpretation made by you. Why should anyone listen to your suggestions, if you don't get the facts right?

Which facts are you referring to: did the LZ experiment find dark matter or has the LHC found dark matter?

 

[Adrian59]

Gravitational acceleration beyond what is expected from visible matter is an observed fact (with multiple lines of evidence). If you exclude modified gravity as an explanation, you are arguing for dark matter.

This is a typical binary response from supporters of the standard model of cosmology: if it's not them its us.

Which ones? Please give specific references.

As an example: consider galaxy rotation curves. The problem is using a simplistic version of Newton's law of gravity which works fine for our solar system with only eight significant bodies orbiting a sun which contains 99.8% of the mass at the very centre. However, galaxies are more complicated; our own milky way contains hundreds of billions of stars all roughly the same order of mass. So that when more finessed methods of derivation are used: hey presto one gets the right rotation curve. I have mentioned this before in PF - search me and find the refs.

 

[Adrian59]

No, but that’s the point. It is exactly the absence of CP violation in the strong sector that motivates the original axions.

But, this still means that strong CP violation is hypothetical.

 

[Adrian59]

That is simply false. In particular models with particular assumptions and particular production mechanisms perhaps, but in general nowhere close to true.

I am not sure which assumptions you are referring to. The graph is between cross section and mass. Presumably dark matter particle have mass. I presume they would need some cross section to have any hope of detection. If the cosmology community are going to give up on that this leads into an entirely different philosophical territory.

 

[Orodruin]

I am not sure which assumptions you are referring to. The graph is between cross section and mass. Presumably dark matter particle have mass. I presume they would need some cross section to have any hope of detection. If the cosmology community are going to give up on that this leads into an entirely different philosophical territory.

Every such graph has assumptions regarding the model behind it. It is never as simple as just a cross section vs mass regardless of how much some people would like to present it as such.

Edit: And on top of that, these graphs never really show the entire parameter space which is workable within a model either, as described above.

 

[jedishrfu]

It seems this is a good time to close this thread, and the OPs question has been answered.