Status of Dark Matter in the Universe [CEA]

Courtesy of arXiver, here’s a nice review article if you want to get up to date with the latest ideas and evidence about Dark Matter…

arXiver

http://arxiv.org/abs/1701.01840

Over the past few decades, a consensus picture has emerged in which roughly a quarter of the universe consists of dark matter. I begin with a review of the observational evidence for the existence of dark matter: rotation curves of galaxies, gravitational lensing measurements, hot gas in clusters, galaxy formation, primordial nucleosynthesis and cosmic microwave background observations. Then I discuss a number of anomalous signals in a variety of data sets that may point to discovery, though all of them are controversial. The annual modulation in the DAMA detector and/or the gamma-ray excess seen in the Fermi Gamma Ray Space Telescope from the Galactic Center could be due to WIMPs; a 3.5 keV X-ray line from multiple sources could be due to sterile neutrinos; or the 511 keV line in INTEGRAL data could be due to MeV dark matter. All of these would require further confirmation in other experiments…

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23 Responses to “Status of Dark Matter in the Universe [CEA]”

  1. “arXiv admin note: text overlap with arXiv:1010.2642 by other authors without attribution”

    I don’t know how reliable these automatic notes are—in particular, how high the false-positive rate is—but this might be an interesting example to check.

    • arXiv:1010.2642, section 9.2.1:

      About axions, the good news is that cosmologists do not need to “invent” new particles. Two candidates already exist in particle physics for other reasons: axions and WIMPs. Axions with masses in the range 10􀀀(3􀀀6) eV arise in the Peccei–Quinn solution to the strong-CP problem in the theory of strong interactions.

      arxiv: 1701.01840, section 4.3:

      The good news is that cosmologists don’t need to “invent” new particles. Two candidates already exist in particle physics for other reasons: axions and WIMPs. Axions arise in the Peccei-Quinn solution to the strong-CP problem in the theory of
      strong interactions,30 and are suitable dark matter candidates31,32 if the mass lies in the range ma 10􀀀(3􀀀6) eV.

      arXiv:1010.2642, section 9.2.1:

      WIMPs are also natural dark matter candidates from particle physics. These particles, if present in thermal abundances in the early universe, annihilate with one another so that a predictable number of them remain today. The relic density of these particles comes out to be the right value:

      DMh2 = (3 10􀀀26cm3=s)=hviA (124)

      where the annihilation cross-section hviA of weak interaction strength automatically gives the right answer. The reason why the final abundance is inversely proportional to the annihilation cross-section is rather clear: the larger the annihilation cross-section, the more WIMPs annihilate and the fewer of them are left behind. Furthermore, annihilation is not eternal: owing to the expansion of the universe, annihilation stops when its rate becomes smaller than the expansion rate of the universe. When this happens, the abundance is said to freeze-out.

      This coincidence is known as ‘the WIMP miracle’ and is the reason why WIMPs are taken so seriously as DM candidates. The best WIMP candidate is motivated by Supersymmetry (SUSY): the lightest neutralino in the Minimal Supersymmetric Standard Model. Supersymmetry in particle theory is designed to keep particle masses at the right value. As a consequence, each particle we know has a partner: the photino is the partner of the photon, the squark is the quark’s partner, and the selectron is the partner of the electron. The lightest superysmmetric partner is a good dark matter candidate.

      arxiv: 1701.01840, section 4.4:

      WIMPs are thought to be good dark matter candidates from particle physics for two reasons. They are dened to be particles that participate in weak interactions (but not strong or electromagnetic) and their masses are in the range GeV{10 TeV. These particles, if present in thermal abundance in the early universe, annihilate with one another so that a predictable number of them remain today. The relic density of these particles comes out to be the right value:

      h2 = (3 10􀀀27cm3=sec)=hviann : (1)

      Here h is the Hubble constant in units of 100 km/s/Mpc, and the annihilation cross section hviann of weak interaction strength automatically gives the correct abundance of these particles today. This coincidence is known as \the WIMP miracle” and is the rst reason why WIMPs are taken so seriously as dark matter candidates.

      Secondly, WIMP candidates automatically exist in models that have been proposed to resolve problems in theoretical particle physics. These models contain WIMPs as a byproduct of the theory. For example WIMP candidates exist in supersymmetric models (SUSY), including the lightest neutralino in the minimal supersymmetric standard model. Supersymmetry in particle theory is designed to keep particle masses at the right value. As a consequence, each particle we know has a partner: the photino is the partner of the photon, the squark is the quark’s partner, and the selectron is the partner of the electron. The lightest superysmmetric partner is a good dark matter candidate.

      One doesn’t have to be a lawyer to conclude that this is inexcusable plagiarism. Note that both reviews are single-author papers. (Overlap between papers which also have an overlap of authors is OK in my view. If one has come up with the best way to say something and needs to say it again (rather than just citing the other paper, which is not always sufficient), then there is no problem in using one’s own text again.

      ================================================

      OK, these are reviews, so it is not like Freese is claiming for herself results discovered by Riotto. What would happen to a student who committed plagiarism at this level? What will happen to Freese? What will happen to me? 😐 At the very least, an apology to Riotto is due, and the paper on arXiv should be a) replaced with a version omitting the plagiarism and b) with a note both in the “abstract” and in the paper noting why it was replaced and apologizing.

      Of course, this assumes that Freese copied from Riotto, not that both copied from a common source. (But even in that case, Freese would be guilty of plagiarism.)

  2. John Peacock Says:

    I once encountered a related case as a journal editor. We received a complaint from scientist X that scientist Y had reproduced verbatim a sequence from one of X’s papers. Y’s response was that (A) the paper by X had been cited; (B) the passage in question was being given by way of background review rather than claimed as original. I thought this was pretty thin ice, but what swayed the case away from outright removal of the paper was examination of the TeX source. Although there was quite a long sequence of equations that looked identical in print, the TeX commands to implement them were really quite different. So this was plagiarism involving intellectual effort, rather than just by cut-and-paste. You might say that plagiarism is plagiarism period, but there must be a special circle of hell reserved for the use of cntrl-C cntrl-V. Plagiarism of ideas is murkier territory: as Tom Lehrer memorably stated, all research involves this to some extent.

    • I agree that literal cut and paste is worse. Sometimes, there is only one good way to say something. However, in the example above I am sure that it is not coincidental. (Modifying it slightly, as above, also rules out the “I just forgot the quotation marks” defense.)

    • telescoper Says:

      I usually prepare for writing articles by writing the main equations (some of which would come from other sources) out in longhand and making rough notes about what should be written in between. I find that gives a better sense of the shape of the article than sitting down at the screen and starting from scratch. An approach like that in a review article might lead to the result you describe. It’s remiss not to include a reference when you quote a result, but it may be error rather than misconduct. Copying and pasting chunks of text is much harder to explain.

      I do remember once, about 20 years ago, writing the introduction to a paper (which had a few co-authors). In the first or second sentence I included a nicely turned phrase which just popped into my head.

      It turns out that this phrase had appeared very recently in another paper (which we had cited). I had honestly forgotten where it came from and fooled myself into thinking that I was smart enough to think it up myself.

      The author of that other paper contacted me, we discussed it and the matter was settled amicably, though I was quite perturbed by the whole affair.

      That, however, was just part of a sentence rather than several entire paragraphs!

    • “I thought this was pretty thin ice, but what swayed the case away from outright removal of the paper was examination of the TeX source. Although there was quite a long sequence of equations that looked identical in print, the TeX commands to implement them were really quite different. So this was plagiarism involving intellectual effort, rather than just by cut-and-paste.”

      If the TeX source wasn’t available, this would explain the different coding here even though the text was the same.

      Actually, it’s probably OK to cut and paste TeX source for equations. At least, all other forms of plagiarism are worse.

  3. telescoper Says:

    To be honest I didn’t realise that the arXiv did plagiarism-checking at all. It’s a positive development, I think.

  4. John Peacock Says:

    Does WordPress check whether you stole your posts from other blogs???

  5. John Peacock Says:

    I knew that arXiv checked. What I don’t know is if there is any way to pre-check your manuscript before submission. That would be a useful facility: then you could avoid inadvertent embarrassments like your own earlier example. But maybe then that would open the door for people to doctor any deliberate plagiarism until it was just below threshold.

    • telescoper Says:

      That’s how Turnitin works for online coursework submissions by undergraduates. It wouldn’t be too difficult to get a similar system on the arXiv.

  6. I do think that the “WIMP miracle” has been oversold. IF WIMP miracle was correct, we should have seen a WIMP-proton x-section of 10^{42} cm^2

  7. telescoper Says:

    I have been in communication with Katherine Freese about this. She sent me this comment by email and asked me to post the content here:

    This is serious. I’ve been accused of plagiarism in my latest paper on the physics arXiv, and the issue was even brought up to the ethics division at the University of Michigan. In fact, the problem is the other way around. My supposed plagiarism is actually based on plagiarism by Riotto of my earlier dark matter review in 2008. The entire Dark Matter section in his 2010 paper 1010.2642 consists entirely of words repeated verbatim from Freese http://lanl.arxiv.org/abs/0812.4005 without attribution.

    I reuse my own text from one review to the next. I will now produce a version 2 of my recent paper 1701.01840 in which I reference my own previous review, the original source of the repeat paragraphs. I probably used the same text in an even earlier review article. All of these reviews are conference proceedings.

    I don’t like to post this, but I must protect my reputation.

    The issue has also been investigated by the arXiv team who wrote the following to Professor Freese:

    After examining your overlap claim, we have removed the overlap notice from arXiv:1701.01840, and applied it to arXiv:1010.2642. We apologize for the inconvenience.

    It is now very clear that Professor Freese is not the one guilty of plagiarism.

    • telescoper Says:

      It also appears that Professor Riotto has now modified his paper to include a reference to Professor Freese’s earlier paper.

      • To whit: “This section is taken verbatim from Freese [20]”. This is no longer plagiarism, but still appears to be copyright infringement and, well, rude.

      • telescoper Says:

        Yes, I saw that. It’s hardly a satisfactory response.

      • Revising the paper to remove the plagiarism now would probably be worse; people would notice it only by comparing with the previous version, unless this were mentioned in the abstract. Now, anyone reading the paper (not that likely for an old conference paper; probably this discussion has provoked more reads than in the last 5 years) will see “copied verbatim”. At least it now says so in the paper, and people reading it can draw their conclusions. It is rare to say “copied verbatim”, so there is really little need for interpretation. It would have been better to mention the reason for the added reference in the abstract. (I know of another case where a complaint led to a replacement, but the abstract just says “reference added”, rather than saying why (it changed an important claim in the paper). Who will read the new version based on “reference added”? This means to set the record straight, one has to write a new paper saying what the paper in question got wrong and why the reference was added. More about this anon.)

    • I’m glad that it got cleared up! To be fair, I wrote: “A variant of the common-source scenario is that Riotto got his text from an even earlier text from Freese (bad) while Freese merely re-used her own text (OK).”

      I think it is perfectly acceptable to re-use one’s own text, especially in review articles for conferences. I have done so myself.

      Maybe this will lead to arXiv fine-tuning their automatic plagiarism-detection mechanism. As mentioned, though, a preview function might lead to plagiarists altering the copied text just enough that it is no longer detected. I suggest that authors check their submission and complain to arXiv if there is an unjust accusation.

      Considering that Freese’s earlier paper is on the arXiv, it is disturbing that it was not checked by the automatic mechanism. I have seen notices that a text has overlap with texts by the same author, so in principle one’s own papers are checked as well. The mechanism should have found both earlier instances of the text, and plagiarism warning should have gone to Riotto’s article. I don’t think that the mechanism around back when that article was posted. Perhaps arXiv should go through their, errm, archive and check “historical” papers for plagiarism.

      How can one check for plagiarism without allowing mistakes to creep in (as in this case) without a preview function allowing plagiarists to fine-tune it away? Perhaps best would be not to post such notices at all. Rather, if the detection finds something, the paper should be put on hold (there is already a mechanism for this), arXiv should contact the authors, and if a convincing defense (such as the one by Freese in this case) is not presented, then the author should be banned. The question is whether banned immediately forever, or some “three strikes and your out” policy, or banned for a certain time. (Banning the paper in question wouldn’t work since it could be recycled into another submission.)

  8. Even in Riotto’s Introduction, he manages to sleight Freese by omitting her input saying, “Since these lectures were delivered at a school, we shall not provide an exhaustive list of references to original material, but refer to several basic cosmology books and reviews where students can find the references to the original material [1–8],” again excluding her contribution to his paper even in his updated mea culpa version.

    • At least in textbooks I think it is OK to omit citations in the text and even not to include all original sources in the references, but rather just a few important ones and reviews and so on which do contain exhaustive references to the original literature. Conference proceedings are often limited in page numbers, and if the arXiv version is to match the published one, exhaustive references might lead to too little text. (I have a conference proceeding with a long author list and, as only one page was allowed (it was a poster), the printed version contains just the title block and a (now defunct) URL to an online copy of the poster! (The poster is still available online, but I can’t update the link in the paper proceedings.))

      At the same time, copying something verbatim, or even almost verbatim, is not acceptable, and if one makes substantial use of another paper, one should cite that paper even if one does not cite all sources.

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