Dark Matter

  • #1
Simon Peach
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I would like to hear what the opinions are.
Could sterile neutrino's be dark matter?
I'm sure this has been discussed if not here then somewhere.
 

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  • #2
Orodruin
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This depends on the properties of said sterile neutrino. Sterile neutrinos have certainly been discussed as a dark matter candidate, typically with masses around the keV scale. Did you have a particular mass range in mind?
 
  • #3
Simon Peach
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This depends on the properties of said sterile neutrino. Sterile neutrinos have certainly been discussed as a dark matter candidate, typically with masses around the keV scale. Did you have a particular mass range in mind?
No not a mass. Was just reading that they may have been found by the Liquid Scintillator Neutrino Detector and it seemed that if they are so hard to detect here on Earth then they may be a candidate for Dark Matter.
 
  • #4
Orodruin
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No not a mass. Was just reading that they may have been found by the Liquid Scintillator Neutrino Detector and it seemed that if they are so hard to detect here on Earth then they may be a candidate for Dark Matter.
So implicitly you are assuming a mass scale, that of the hypothetical sterile suggested as a reason for the LSND anomaly. No, that sterile cannot be dark matter. It has several issues with cosmology. Also note that the LSND experiment is rather old and its results have been known for a long time. Its interpretation in terms of a sterile neutrino is doubtful based on the global experimental status. You may have been alerted by the latest results of MiniBooNE, which are discussed here.
 
  • #5
sadovnik
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dark matter must consist of some kind of unseen particles
Dirac called these unseen particles '' negative virtual particles''
and wrote them by the formula: -E=Mc^2
===
 
  • #6
Orodruin
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dark matter must consist of some kind of unseen particles
No it must not.

Dirac called these unseen particles '' negative virtual particles''
No he did not. You are confusing dark matter with the idea of a Dirac sea.
 
  • #7
sadovnik
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Every matter consists of particles.
What does dark matter consist of ?
===
 
  • #8
Orodruin
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Every matter consists of particles.
Not necessarily. You need to go quite far beyond B-level to understand what is meant by "matter" in the context of cosmology and astrophysics.

What does dark matter consist of ?
We do not know. Particle dark matter is a popular theory, but it has not been experimentally verified.
 
  • #9
Chronos
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There is still plenty of evidence remains favoring sterile neutrinos as dark matter. Unexplained xray emission lines from galactic clusters are probably the best evidence to date for sterile neutrino DM. Factors which also favor sterile neutrino dark matter include pulsar kicks and galactic density profiles which suggest central DM cusps over DM core cusps. Astronomical data currently suggests warm DM may be preferred over cold DM models The best evidence may yet come from the LHC, once it reaches the !4 TEV range as planned in 2025 - re: https://arxiv.org/abs/1703.01934, Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC.
 
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  • #10
Adrian59
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There is still plenty of evidence remains favoring sterile neutrinos as dark matter. Unexplained xray emission lines from galactic clusters are probably the best evidence to date for sterile neutrino DM. Factors which also favor sterile neutrino dark matter include pulsar kicks and galactic density profiles which suggest central DM cusps over DM core cusps. Astronomical data currently suggests warm DM may be preferred over cold DM models The best evidence may yet come from the LHC, once it reaches the !4 TEV range as planned in 2025 - re: https://arxiv.org/abs/1703.01934, Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC.

My understanding of any type a neutrino being dark matter is that since neutrinos travel at close to the speed of light they can only be considered as candidates for hot dark matter. It is, also, disappointing that theorists are always suggesting that the answer is just over another hill be it higher energies at LHC or a bigger vat of Xenon.
 
  • #11
Chronos
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That argument argument originated when neutrinos were believed to be massless and simulations ruled out hot [relativistic] neutrinos as the principle form of DM. The argument has become more one of how much mass is necessary to rule out neutrinos as a viable DM candidate. The unidentified xray line in cluster spectrographs has pegs the prospective DM neutrino mass at around 7 Kev - more than enough to refute the hot DM objection. If the sterile neutrino is confirmed, it could be even more massive.
 
  • #12
Adrian59
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That argument argument originated when neutrinos were believed to be massless and simulations ruled out hot [relativistic] neutrinos as the principle form of DM. The argument has become more one of how much mass is necessary to rule out neutrinos as a viable DM candidate. The unidentified xray line in cluster spectrographs has pegs the prospective DM neutrino mass at around 7 Kev - more than enough to refute the hot DM objection. If the sterile neutrino is confirmed, it could be even more massive.

I am still not convinced. I am aware that neutrinos have mass but this is very small and as I believe they still travel at close to the speed of light so they should still be considered as relativistic particles. You quoted an energy of 7 KeV but this is a composite of velocity and mass so are these proposed sterile neutrinos low mass and fast moving or high mass and slower which would make them singular neutrinos?
 
  • #13
Orodruin
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I am still not convinced. I am aware that neutrinos have mass but this is very small and as I believe they still travel at close to the speed of light so they should still be considered as relativistic particles. You quoted an energy of 7 KeV but this is a composite of velocity and mass so are these proposed sterile neutrinos low mass and fast moving or high mass and slower which would make them singular neutrinos?
You are thinking of standard model neutrinos, not sterile neutrinos. Sterile neutrinos with a large mass remains a possible dark matter candidate although mixing would have to be very suppressed. However, it should be mentioned that models including sterile neutrino DM are typically rather fine-tuned and the 7 keV line is by no means necessarily from DM annihilation.
 
  • #14
Chronos
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  • #15
Adrian59
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You are thinking of standard model neutrinos, not sterile neutrinos. Sterile neutrinos with a large mass remains a possible dark matter candidate although mixing would have to be very suppressed. However, it should be mentioned that models including sterile neutrino DM are typically rather fine-tuned and the 7 keV line is by no means necessarily from DM annihilation.

Having done a little searching as well as checking the two abstracts of the references Chronos gave, it appears a bit of a fudge to even call these particles neutrinos which apparently only act via gravity and not the weak force, which seems to make them only yet another hypothetical dark matter particle, sharing only a name with the known neutrinos. Maybe giving them half a familiar name was an attempt to gain quicker acceptance rather then just another DM particle.
 
  • #16
Orodruin
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Having done a little searching as well as checking the two abstracts of the references Chronos gave, it appears a bit of a fudge to even call these particles neutrinos which apparently only act via gravity and not the weak force, which seems to make them only yet another hypothetical dark matter particle, sharing only a name with the known neutrinos. Maybe giving them half a familiar name was an attempt to gain quicker acceptance rather then just another DM particle.
I disagree, it is standard nomenclature to call a standard model singlet fermion "sterile neutrino". Also, please note that their introduction is not mainly as a dark matter candidate, but typically as a means of introducing neutrino mass - this is the reason to call them sterile or right-handed neutrinos. Once introduced, these fermions allow a Majorana mass term and its scale essentially determines the possible phenomenology.
 
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  • #17
Adrian59
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I disagree, it is standard nomenclature to call a standard model singlet fermion "sterile neutrino". Also, please note that their introduction is not mainly as a dark matter candidate, but typically as a means of introducing neutrino mass - this is the reason to call them sterile or right-handed neutrinos. Once introduced, these fermions allow a Majorana mass term and its scale essentially determines the possible phenomenology.

I might be getting this wrong but aren't right handed neutrinos, anti-neutrinos.
 
  • #18
Orodruin
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I might be getting this wrong but aren't right handed neutrinos, anti-neutrinos.
Yes and no. It would be more accurate to say that standard model anti-neutrinos are right-handed. Typically, when we talk about right-handed neutrinos we do mean right-handed neutrinos, which is a hypothetical standard model singlet, not right-handed anti-neutrinos.
 
  • #19
Adrian59
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Yes and no. It would be more accurate to say that standard model anti-neutrinos are right-handed. Typically, when we talk about right-handed neutrinos we do mean right-handed neutrinos, which is a hypothetical standard model singlet, not right-handed anti-neutrinos.

Ok, I understand your point. We are living in exciting times in astronomy and I am in no way suggesting that the experiments being planned should not go ahead but I do think that many of the issues dark matter is trying to solve have been solved better without it, and I do not mean by modified theories of gravity.
 
  • #20
Orodruin
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have been solved better without it, and I do not mean by modified theories of gravity.
Please specify, with references. You cannot just throw a statement like this out into the blue. What issues have been solved without dark matter that it is supposed to solve?
 
  • #21
Adrian59
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Please specify, with references. You cannot just throw a statement like this out into the blue. What issues have been solved without dark matter that it is supposed to solve?

I did mention these in a thread last year 'Is there an alternative theory to dark matter?'. The main reference for galaxy rotation curves was J. D. Carrick and F. I. Cooperstock. ‘General relativistic dynamics applied to the rotation curves of galaxies.’ (2012). Astrophysics and Space Science, Vol. 337, Issue 1, pp 321–329.
 
  • #22
Orodruin
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I did mention these in a thread last year 'Is there an alternative theory to dark matter?'. The main reference for galaxy rotation curves was J. D. Carrick and F. I. Cooperstock. ‘General relativistic dynamics applied to the rotation curves of galaxies.’ (2012). Astrophysics and Space Science, Vol. 337, Issue 1, pp 321–329.
You do realize that that is one 7 year old paper that is not very well connected to the rest of the literature? (The papers citing it are peripheral with only one of the citing papers having a large number of citations itself. In that paper, the reference you have provided is not quoted for showing that you can get rid of dark matter.) It also discusses one issue that is solved by dark matter, galaxy rotation curves, and there is a large amount of other evidence.
 
  • #23
Adrian59
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You do realize that that is one 7 year old paper that is not very well connected to the rest of the literature? (The papers citing it are peripheral with only one of the citing papers having a large number of citations itself. In that paper, the reference you have provided is not quoted for showing that you can get rid of dark matter.) It also discusses one issue that is solved by dark matter, galaxy rotation curves, and there is a large amount of other evidence.

I don't consider the age of a paper relevant to its correctness, after all general relativity in 103 yrs old! It may seem like I am a one reference contributor but the response to this reference is always indirect, like yours, in deflecting the argument to somewhere else. If this paper does describe galaxy rotation without additional mass or modifying gravity, should it not be more widely appreciated? Finally, if it is correct then it is a serious challenge to the dark matter paradigm. Granted it is only one issue but I would suggest it is a major issue.
 
  • #24
Orodruin
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I don't consider the age of a paper relevant to its correctness
I never claimed that! You are making a strawman argument here.

What I did do was to look at how the paper is connected to the rest of the literature and compare that to how it should be connected if it had had a significant impact. You can find single published papers that imply many things (just like anti-vaxxers do - even if that paper was withdrawn makes it different), but in making an overall assessment of the current state of the field you need to look at the full picture instead of cherry picking the results you like.

Finally, if it is correct then it is a serious challenge to the dark matter paradigm. Granted it is only one issue but I would suggest it is a major issue
It is the original issue, I would not call it the major issue. To seriously challenge the DM paradigm you would have to show that it really is inconsistent (I have not read the paper in detail so I cannot speak to how much it does that, but if it really did I believe people would have picked up on it more) or offer good and consistent alternatives that deal with all of the observations that currently support DM.
 
  • #25
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after all general relativity in 103 yrs old!
And has thousands of references, building upon it.
If this paper does describe galaxy rotation without additional mass or modifying gravity, should it not be more widely appreciated?
Exactly. So what do we learn from the fact that it was not more widely appreciated? It is probably flawed. And even if not: That would just create more questions than answers, because it wouldn't do anything about the independent ways to measure dark matter, but it would lead to the question where is dark matter if it is not in galaxies.
 
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  • #26
Chronos
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The sterile neutrino is an imminently logical DM candidate. Ir checks all the big boxes; gravitationally attractive, EM non-interactive, and sufficiently abundant (in theory) to be plausible. No one is claiming it is an undeniably proven particle, but, It''s not like there's a lengthy list of more reasonable alternatives.
 
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  • #27
Orodruin
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The sterile neutrino is an imminently logical DM candidate. Ir checks all the big boxes; gravitationally attractive, EM non-interactive, and sufficiently abundant (in theory) to be plausible.
The problem is that, for the model parameters necessary for a sterile neutrino to be dark matter, none of the other problems associated to the neutrino sector are solved, such as neutrino masses. To me, the canonical idea of a sterile neutrino (i.e., the one introduced in order to provide neutrino masses) is not one that leads to a viable dark matter candidate and you need to somewhat tune the mixing with the active neutrinos to both ensure that it is produced in the early universe and that it does not decay too fast. For example, axion dark matter would be a more natural solution in my opinion, as was the idea of a supersymmetric neutralino although it may be doubtful today.
 
  • #28
Chronos
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Acknowledged, the mixing problem has, of course, been reviewed at some length in the literature. The most recent and relevant discussion of it appears to be; / /arxiv.org/abs/1707.04591, US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report. As an added bonus, the sterile neutrino also offers to solve another long standing mystery - the baryon asymmetry problem. This, along with missing satellite galaxies, DM core profiles, and other outstanding CDM puzzles appear to imbue the sterile neutrino with some pretty remarkable explanatory potential. The next decade should shed some light on whether this constitutes progress or just another clever, but, failed DM candidate.
 
  • #29
Orodruin
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the sterile neutrino also offers to solve another long standing mystery - the baryon asymmetry problem.
This is highly doubtful to be honest, at least if you want the same steriles to be responsible for the dark matter as for the baryon asymmetry. Baryogenesis via leptogenesis is a well-known and theoretically viable mechanism to produce the baryon asymmetry. However, the steriles you need for dark matter are typically way too light and mix way too little to do that for you. Instead, you need a hierarchy of scales in the sterile sector where you essentially have one relatively light sterile that mixes very little and is the dark matter candidate and some heavier sterile states that are mainly responsible for neutrino masses and for leptogenesis. I do not find this very economical nor very convincing, even if the only ingredient you need is a set of standard model singlet fermions.

This, along with missing satellite galaxies, DM core profiles, and other outstanding CDM puzzles appear to imbue the sterile neutrino with some pretty remarkable explanatory potential.
The small scale structure problems are not necessarily problems of CDM and could possibly also be attributed to feedback from processes in the baryon sector. Even if that is not the case, there are several possible ways out, one other such way being self-interactions among the dark matter particles.

I may be wrong of course, but to me sterile neutrino dark matter is not among the top candidates, but merely a candidate.
 
  • #30
Adrian59
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And has thousands of references, building upon it.Exactly. So what do we learn from the fact that it was not more widely appreciated? It is probably flawed. And even if not: That would just create more questions than answers, because it wouldn't do anything about the independent ways to measure dark matter, but it would lead to the question where is dark matter if it is not in galaxies.

Your first sentence is tending towards a circular argument. Since it is not widely appreciated, it is assumed flawed and therefore based on that assumption is not widely appreciated. I could ask what 'independent ways to measure dark matter' you know that have proved its existence, directly? Of course you final point is valid but it cuts both ways because if dark matter is not in galaxies where indeed is it, if indeed it does exist?
 
  • #31
Orodruin
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Your first sentence is tending towards a circular argument. Since it is not widely appreciated, it is assumed flawed and therefore based on that assumption is not widely appreciated. I could ask what 'independent ways to measure dark matter' you know that have proved its existence, directly? Of course you final point is valid but it cuts both ways because if dark matter is not in galaxies where indeed is it, if indeed it does exist?
You do realize that a galaxy without dark matter was recently found? (And that this was with standard assumptions) If what you are suggesting were true, then it would affect all galaxies equally. In fact, finding a galaxy without dark matter is one of the stroger indications for drk matter over an overlooked effect or alternative gravitational theories as you could not get rid of the physics but you could potentially strip a galaxy from its dark matter halo.

Of course, it does not directly prove dark matter, but you cannot reasonably suggest to discredit dark matter on the based on your favorite theory if that theory generally gives worse predictions.
 
  • #32
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Your first sentence is tending towards a circular argument. Since it is not widely appreciated, it is assumed flawed and therefore based on that assumption is not widely appreciated.
It was read. If it would have been valid people would probably have built upon that.
There are a few examples of papers that didn't get much attention that turned out to be good later, but the number is very small compared to the millions (!) of publications that have a low quality.
I could ask what 'independent ways to measure dark matter' you know that have proved its existence, directly?
You could ask, but you can also read the Wikipedia article for an introduction and ask more specific questions here.
 
  • #33
Adrian59
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You do realize that a galaxy without dark matter was recently found? (And that this was with standard assumptions) If what you are suggesting were true, then it would affect all galaxies equally. In fact, finding a galaxy without dark matter is one of the stroger indications for drk matter over an overlooked effect or alternative gravitational theories as you could not get rid of the physics but you could potentially strip a galaxy from its dark matter halo.

Of course, it does not directly prove dark matter, but you cannot reasonably suggest to discredit dark matter on the based on your favorite theory if that theory generally gives worse predictions.

You make it sound like I have an exceptional theory but my favoured theory is general relativity. I do know about this galaxy but as you have pointed out one example is not is not proof of anything. The fact that this is a diffuse galaxy may explain this finding.
 
  • #34
Adrian59
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It was read. If it would have been valid people would probably have built upon that.
There are a few examples of papers that didn't get much attention that turned out to be good later, but the number is very small compared to the millions (!) of publications that have a low quality.You could ask, but you can also read the Wikipedia article for an introduction and ask more specific questions here.

You say "It was read" so do I take it you mean that you have read this paper. I have not found any valid criticism of it except one suggestion that it failed to take into account frame dragging but I fail to see this as a valid criticism unless whole galaxies are in the ergosphere of their central super massive black hole. 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.
 
  • #35
Orodruin
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You make it sound like I have an exceptional theory but my favoured theory is general relativity.
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.

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

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