Dark Matter

[Chronos]

The null finding by ice cube is certainly bad news for some of the simpler sterile neutrino models, but, is not fatal to the entire model population. The 7 keV line reported by Bulbul and Boyarsky in 2014, while interesting, also falls a bit short of 'smoking gun' evidence. Once again, it more constrains one fairly simple DM model than the entire parameter space allowed for DM decay. Yes, baryon asymmetry and DM are difficult to reconcile with a single sterile neutrino mass while satisfying cosmological constraints on both phenomenon, but, this does not rule out additional massive sterile neutrinos. In fact, some models require multiple sterile neutrino species to satisfy both dark matter and baryogenesis constraints, not to mention various other considerations. The suboptimal results to date so not seem to have fatally inured injured the case for sterile neutrino DM so much as highlight the fact its secrets are not yielding to early efforts as easily as we might have hoped. The rules and players in the dark sector remain largely unknown and we are still taking baby steps. The next decade looks promising and there is no shortage of ideas on how to make progress.

 

[Adrian59]

Dark matter is in no way inconsistent with GR. In fact, in cosmology and structure formation you need dark matter in GR to obtain the correct predictions from GR.

(I have no problem agreeing with the former point here. Not sure about the second. Simulations are no substitute for observation and as I believe there has to be initial assumptions for any simulation.)

This is a bit naive in my opinion. What he clearly means is that the appropriate community read the paper and its reaction was to not pick up on it. There can be several reasons for this, but the most likely being that the community did not find it very relevant. There is no circular argument here, claiming there is does not make it true.

I am sure you are aware of confirmation bias and could this be why papers disagreeing with the dark matter paradigm don't get the attention they should. I think one of the contributors to this thread should have another look at this paper and not assume it was adequately viewed the first time. It may have a glaring error that I am unaware of but, if not, what is not to like about it: it solves a astronomical problem without having to invent additional mass or alter accepted physical laws. As Einstein said, "Everything should be made as simple as possible, but not simpler." I know it requires at least some appreciation of a Bessel function which is more familiar to engineers than physicists and could be why most physicists shy away from it.

 

[Orodruin]

what is not to like about it: it solves a astronomical problem without having to invent additional mass or alter accepted physical laws

I think this has been pointed out over and over in this thread already: Doing so is not very consistent with other observations. You "solve" a single problem whereas dark matter solves significantly more problems.

I know it requires at least some appreciation of a Bessel function which is more familiar to engineers than physicists and could be why most physicists shy away from it.

This is pure conjecture and has absolutely nothing to do with what has been said in this thread. It is also directly counterfactual in my case, which you might realize by checking out the table of contents of my book.

In fact, some models require multiple sterile neutrino species to satisfy both dark matter and baryogenesis constraints, not to mention various other considerations.

Is this not just what I said?

Once again, it more constrains one fairly simple DM model than the entire parameter space allowed for DM decay.

This is the same type of argument that SUSY proponents use for keeping neutralino dark matter alive.

All I am saying is that I do not see sterile dark matter as an outstanding candidate in relation to other possibilities. If you had me guess at this time, my money would be on axion or axion-like dark matter. Sterile neutrinos are natural components in an extended standard model, but the canonical seesaw implementation does not lead to them being dark matter.

In fact, some models require multiple sterile neutrino species to satisfy both dark matter and baryogenesis constraints, not to mention various other considerations.

I assume you are thinking of nuMSM? It needs to be quite fine-tuned in my experience even if it remains a theoretical possibility.

 

[mfb]

You say "It was read" so do I take it you mean that you have read this paper.

That is not what I said. As Orodruin explained: It was read by the relevant experts.

If there are more specific technical criticisms of the paper then now might be a good time to make these known, otherwise the derivation, surely, stands.

You can write 10 bad papers in the time you can properly refute one of them, and the number of people who can write bad papers is much larger than the number of experts. "No one took the time to refute my pet theory" is not a sign that it would have any merit.

I am sure you are aware of confirmation bias and could this be why papers disagreeing with the dark matter paradigm don't get the attention they should.

You misunderstand the situation. Everyone would be happy to find some new explanation because the current situation is the worst case - we know something is missing but we don't know what. But so far no one found a new explanation that looks good.

 

[Adrian59]

I think this has been pointed out over and over in this thread already: Doing so is not very consistent with other observations. You "solve" a single problem whereas dark matter solves significantly more problems.

Dark matter only does half the job. I am not a proponent of any type of modified gravity theory. Since general relativity describes gravity as a direct consequence of mass there is no problem explaining the Tully-Fisher relationship (Stacy S. McGaugh, Federico Lelli, and James M. Schombert, (2016). ‘The Radial Acceleration Relation in Rotationally Supported Galaxies) something dark matter has significant problems with. Also, an unmodified general relativity would fit the work of Radosław Wojtak et al just as well with or without dark matter.

As for galaxy clusters, for brevity, I am just going to point out that although mass discrepancy has been found this does not necessarily imply exotic matter. No dark matter has been found in the near universe - on earth, in the solar system or in our local area of the MW (Moni Bidin, C., et al (2012). ‘Kinematical and chemical vertical structure of the Galactic thick disk. II. A lack of dark matter in the solar neighbourhood.’ Astrophysical Journal). It would be strange if the only place that has dark matter was the distant universe.

 

[Adrian59]

That is not what I said. As Orodruin explained: It was read by the relevant experts.

Apologies, I missed off the question mark. It was a question not a statement.

 

[Chronos]

@Adriqn59 IIRC, the op and every other poster in this thread has been centered on sterile neutrinos as a DM candidate, not the general feasibility of DM. Perhaps starting a thread centered around your own interests would be more constructive than hijacking this thread.

 

[Adrian59]

@Adriqn59 IIRC, the op and every other poster in this thread has been centered on sterile neutrinos as a DM candidate, not the general feasibility of DM. Perhaps starting a thread centered around your own interests would be more constructive than hijacking this thread.

After reviewing the conversation so far, I don't consider myself as' hijacking' this thread. There is a natural progression to where we are now. I did originally discuss the idea of sterile neutrinos but then I must admit I made an off the cuff remark and was challenged to provide a reference to which I did. If the conversation has moved territory and now constitutes a new subject, then I have no problem in starting a new thread. I'll think of a title to attract a wider involvement.

 

[Chronos]

The axion has also proven elusive, as discussed here; https://arxiv.org/abs/1708.06367, Overview of the Cosmic Axion Spin Precession Experiment (CASPEr). And ,yes, nuMSM is a model that includes multiple sterile neutrino species.

 

[Orodruin]

And ,yes, nuMSM is a model that includes multiple sterile neutrino species.

This does not really answer the question of whether it was what you were thinking about or the issue that it is rather fine-tuned. I somehow get the feeling from your posts that you think I do not know this already. Correct me if I am wrong.

 

[Chronos]

Yes, nuMSM is the model I had in mind, although. I admit to believIng any successful DM model will have difficulty evading the appearance of some degree of fine tuning. Nature has a capricious predilection for that sort of thing, IMO. I don't think you are unfamiliar with any of the issues raised, quite the contrary - and certainly not less familiar than I. I am occasionally, in some cases, more familiar with recent literature than some, but, my interest is in sorting wheat from chaff, not being pretentious. I only have an undergraduate level of understanding and all too often miss important caveats even when fish slapped with them.

 

[Adrian59]

All I am saying is that I do not see sterile dark matter as an outstanding candidate in relation to other possibilities. If you had me guess at this time, my money would be on axion or axion-like dark matter. Sterile neutrinos are natural components in an extended standard model, but the canonical seesaw implementation does not lead to them being dark matter.

I believe some recent astronomical observations had nearly ruled out ALPs. Apologies this time, as I haven't got the reference, though I thought you would maybe know the paper I refer to.

 

[Chronos]

The tightest constraints on axions that I know about are devived frrom laboratory results, not ast5ronomicl observations, as disussed here' https://phys.org/news/2018-02-dark-matteraxions-ever-fewer.html, It may be a liitel early to view this as ruling out axion DM, but, it does serously limit the energies at which may be hiding. I don't doubt there are astronomical observations as well, but, I don't believe any such data is as suffocating as this one.

 

[Adrian59]

The tightest constraints on axions that I know about are devived frrom laboratory results, not ast5ronomicl observations, as disussed here' https://phys.org/news/2018-02-dark-matteraxions-ever-fewer.html, It may be a liitel early to view this as ruling out axion DM, but, it does serously limit the energies at which may be hiding. I don't doubt there are astronomical observations as well, but, I don't believe any such data is as suffocating as this one.

Thanks for the reference, though it would appear axions may be going the same way as WIMPs with an ever decreasing search area.

 

[Orodruin]

Thanks for the reference, though it would appear axions may be going the same way as WIMPs with an ever decreasing search area.

If you had read the article properly you would have realized that experiments have not even begun to really touch the canonical QCD axion. And that does not even begin to be the entire axion-like particle dark matter parameter space.

 

[Chronos]

I increasing convinced that no single particle species can satisfactorily account for the dark sector any more than a single particle species is sufficient to account for the baryon sector. It appears reasonable to consider the neutrino as a card carrying member of the dark sector and probably so is the Higgs. With that in mind, multiple DM particles does not look like a particularly risky prospect, IMO. Unsurprisingly, this has been considered, as evidenced here; https://arxiv.org/abs/1204.0514,
Multiple Dark Matter as a self-regulating mechanism for dark sector interactions.

 

[Vanadium 50]

It appears reasonable to consider the neutrino as a card carrying member of the dark sector and probably so is the Higgs.

The Higgs is too short-lived to be part of the dark sector.

 

[Chronos]

Yes, but, I do not view that as precluding it from being part of the dark sector - especially if it confers mass to dark sector particles.

 

[Orodruin]

Yes, but, I do not view that as precluding it from being part of the dark sector - especially if it confers mass to dark sector particles.

The Higgs field is not dark, it is most certainly interacting with Standard Model particles (and it also gives mass to weak gauge bosons and fermions!). That said, you may be thinking about the Higgs portal, which is a collective name for models where the main interactions between the Standard Model and the dark sector are mediated by the Higgs. Also, when you build models it is very difficult to build models where the dark matter does not interact via the weak interaction, but interacts with the Higgs, since the Higgs is an $SU(2)_L$ doublet - at least if you care about gauge invariance.

 

[Chronos]

Given DM has mass, it is easy to make the leap and assume the Higgs interacts with dark sector particles. Of course that hinges upon the Higgs accoutning for all mass, which may be debatable.

 

[Orodruin]

Given DM has mass, it is easy to make the leap and assume the Higgs interacts with dark sector particles. Of course that hinges upon the Higgs accoutning for all mass, which may be debatable.

Very debatable. A majority of dark matter models that I am aware of does not give DM mass through EW symmetry breaking.

Edit: In fact, it is so debatable that it sounds to me like any such model would be severely constrained.

 

[Dale]

Closed while the mentors discuss.

Edit: After discussion, it will remain closed since it has gone so firmly off topic.