The discussion revolves around the candidacy of sterile neutrinos as a potential form of dark matter, exploring various properties, implications, and evidence related to this hypothesis. Participants examine theoretical aspects, experimental findings, and the broader context of dark matter research.
Participants do not reach a consensus on the candidacy of sterile neutrinos as dark matter. Multiple competing views remain, with some supporting the idea and others challenging it based on various theoretical and experimental considerations.
The discussion highlights limitations in the understanding of dark matter, particularly regarding the properties and behaviors of sterile neutrinos, and the dependence on experimental results that may be subject to interpretation.
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.Orodruin said: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?
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.Simon Peach said: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.
No it must not.sadovnik said:dark matter must consist of some kind of unseen particles
No he did not. You are confusing dark matter with the idea of a Dirac sea.Dirac called these unseen particles '' negative virtual 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.sadovnik said:Every matter consists of particles.
We do not know. Particle dark matter is a popular theory, but it has not been experimentally verified.sadovnik said:What does dark matter consist of ?
Chronos said: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.
Chronos said: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.
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.Adrian59 said: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?
Orodruin said: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.
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.Adrian59 said: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.
Orodruin said: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.
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.Adrian59 said:I might be getting this wrong but aren't right handed neutrinos, anti-neutrinos.
Orodruin said: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.
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?Adrian59 said:have been solved better without it, and I do not mean by modified theories of gravity.
Orodruin said: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?
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.Adrian59 said: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.
Orodruin said: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 never claimed that! You are making a strawman argument here.Adrian59 said:I don't consider the age of a paper relevant to its correctness
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.Adrian59 said: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
And has thousands of references, building upon it.Adrian59 said:after all general relativity in 103 yrs old!
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.Adrian59 said:If this paper does describe galaxy rotation without additional mass or modifying gravity, should it not be more widely appreciated?
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.Chronos said: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.
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.Chronos said:the sterile neutrino also offers to solve another long standing mystery - the baryon asymmetry problem.
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.Chronos said: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.
mfb said: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.