How the Higgs can lead us to the dark universe

The media frenzy surrounding the Higgs discovery announcement has on the whole consisted of stories that reasonably accurately deal with the scientific implications. Journalists have for instance by now learned that “string theory predictions” are a good thing to ignore. As usual though, theoretical physicists themselves can be counted on to inject some misleading hype into the press coverage when they get a chance.

Sean Carroll is doing his part, with a new piece at CNN entitled How the Higgs can lead us to the dark universe, which begins:

The incredible discovery of the Higgs boson will open up new ways of probing the part of the universe that is invisible to our everyday senses: beyond ordinary matter, into the extraordinary world of dark matter.

Since most people just read the title and first paragraph of stories like this, CNN’s readers will likely go away believing that Carroll’s favorite speculative hypothesis, one which hasn’t been working out very well, is the important significance of the Higgs discovery. What he’s referring to are “Higgs-portal” models of WIMP dark matter. For examples of some recent papers discussing what the LHC has to say about such models, see here and here. In recent years experimental results have not been kind to these models. Negative recent results from direct detection experiments like Xenon100 haven’t helped, nor have negative results from monoject searches at the LHC. The significance of the Higgs discovery for the Higgs-portal to dark matter idea is not that it provides evidence for this, but quite the opposite. Seeing signal sizes in various channels that roughly agree with the SM puts new limits on this kind of idea (because if it were true the branching ratios would be non-SM, as the Higgs had a new and potentially large possible decay channel to dark matter particles). Since one can construct a wide range of possible models of dark matter of this kind, many with behavior indistinguishable from the SM, there’s no way to rule them out completely. It’s of course possible that detailed future studies of the Higgs will find non-SM branching ratios that give evidence for a coupling to dark matter. My impression though is that most theorists find this rather unlikely, and I’d be curious to know what probability Carroll assigns to the idea that he is promoting. Back in 2008, he gave 15% as the probability for any kind of evidence of dark matter at the LHC, and the negative results about SUSY (which he assigned 60% probability) rule out many of the most popular models with LHC-visible dark matter.

Carroll has a new book coming out about the Higgs in November, The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World. The table of contents and the description of the book here look quite promising, but unfortunately he seems to have decided that the way to market a book about the Higgs story is with the dark matter hype:

A doorway is opening into the mind boggling, somewhat frightening world of dark matter. We only discovered the electron just over a hundred years ago and considering where that took us—from nuclear energy to quantum computing—the implications of the Higgs discovery hold the potential of changing the world.

I’m somewhat curious to know why dark matter is “frightening”. In Carroll’s last book the big speculative idea being marketed was the multiverse, it’s interesting to see that he’s chosen to move away from that particular mania to much more solid physics, although keeping it hype-free seems to be too much to ask.

First out of the gate post-discovery with a book about the Higgs won’t be Carroll, but maybe Lisa Randall, with an e-book entitled Higgs Discovery: The Power of Empty Space, which I know nothing about, other than that it’s supposed to be available Tuesday. Presumably it’s an update of material in her recent Knocking on Heaven’s Door, where, like Carroll, she moved away from the highly speculative material about extra dimensions of her first book, Warped Passages.

I have seen an early version of one quite good new book about the Higgs, Jim Baggott’s Higgs: The Invention and Discovery of the ‘God Particle’, which is scheduled to be released August 13 in the UK, September 6 in the US and the US. It will come with a foreword by Steven Weinberg, which is already available here.

Update: Over at Resonaances, Jester, who is an expert on this topic, comments:

Finally, a simple and neat theory of dark matter that annihilates or scatters via a Higgs exchange, the so-called Higgs portal dark matter, is getting disfavored because Higgs would have a large invisible branching fraction, and thus a suppressed rate of visible decays.

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18 Responses to How the Higgs can lead us to the dark universe

  1. Pingback: XENON100 hat immer noch keine WIMPs gefunden « Skyweek Zwei Punkt Null

  2. Yatima says:

    > dark matter is “frightening”

    You wouldn’t be relaxed if a solar-mass neutralino ball were wandering into the Solar System! 😉

  3. higgs+bsm says:

    Many books and articles tell about the Higgs and the SM, essentially the search for the Higgs as the culmination of the quest to find all the pieces of the SM. That is well and good, to explain the SM to the lay public. But to do so it is at the same time also to look backwards, at what has already been accomplished, not to look forwards to ask ‘what next’? So Sean Carroll has his take, and perhaps Kaku and Kane, etc. have even more outrageous pet ideas to peddle. Consider the hype that was promoted after WW2: everyone assumed that nuclear power was the unquestioned energy source of the future. And indeed millions (of not billions) were spent on nuclear power plants. Now that was real hype. Go to CNN and broadcast an interview “The Higgs is the culmination of a decades-long search to find all the pieces of the SM. Now we have (almost certainly) found it. It is a magnificent accomplishment, and it provides us with no clues at to what comes next, it says nothing about dark matter, or dark energy, and provides no pointers as to where to look for the next level of particle physics.” See what happens.

  4. Tammie Sandoval says:

    I have a question on dark matter.

    When certain experiments first detected dark matter, an alternative theory was offered: That theory held that dark matter is an illusion. Instead, the experiments are explained if the simple law of gravity is incorrect, at least at long distances.

    Has this alternative theory been falsified?

  5. Peter Woit says:


    The whole issue of “dark matter” is quite complex, with many alternative sorts of explanations of the phenomenon. I’m no expert, so not competent to moderate a discussion of this large topic here. Look elsewhere for debates about “MOND”, a modification of GR to accomodate the effects ascribed to dark matter. My impression is that such GR modifications both look rather ad hoc and don’t agree with some astrophysical evidence. But you really need to consult an expert…

  6. Will says:

    Carroll’s most recent blog post is about the Xenon100 results:

    He certainly admits it’s evidence against the “provocative hints” he though previous experiments showed, and although I don’t understand any dark matter physics well enough to say whether this was much of an oversight, he makes no connection to the Higgs or his theories about it’s dark matter interactions.

  7. SpearMarktheSecond says:

    Or, maybe the dark matter particle doesn’t couple to the Higgs. I thought one of the components of the neutralino (the Bino?) did exactly that.

  8. David Nataf says:

    The Higgs has to couple to dark matter as dark matter particles necessarily have mass. If there’s no coupling of the Higgs to dark matter then it’s not a standard model Higgs.

    Peter, MOND is a modification to newtonian gravity not to GR, hence the name “modified newtonian dynamics”. The relativistic extension of MOND is TeVeS, I don’t know that it’s the unique extension.

  9. truth says:

    Daniel Nataf, that is not true.
    The Higgs is part of the Standard Model; it must give mass to the Standard Model particles.
    How the dark matter acquires mass is unknown; that requires an understanding of physics beyond the Standard Model.
    It is conceivable that its mass comes from the Higgs, but quite possible for it not to also – for instance, the axion acquires mass from QCD effects separate from the Higgs.

  10. In Hell's Kitchen (NYC) says:

    IMO, Carroll is the quintessential blog scientist…as a sci-fi fan I wouldn’t count anything he writes for more than its entertainment value or its value as a seed idea for a good novel.

  11. Tmark48 says:

    higgss+bsm wrote : “It is a magnificent accomplishment, and it provides us with no clues at to what comes next, it says nothing about dark matter, or dark energy, and provides no pointers as to where to look for the next level of particle physics. See what happens.”

    Frankly who cares if the field of HEP comes to a halt (except for high energy physicists that is) ? The LHC by itself will be productive for a good decade even if no new physics is discovered beyond the SM. Is this the end of physics ? Not by a long shot, physics even fundamental or theoretical physics is not reduced to HEP.


    People that believe this have a very distorted view of physics. Progress in astronomy will continue to be made, LHC or no LHC. As for dark matter, building better detectors in astronomy could provide an answer as to its nature. Why not neutrinos as dark matter ? They are massive and interact very weakly with ordinary matter. Progress in quantum mechanics will continue to be made, wether or not we nail down a consistent theory of quantum gravity if this is even possible at all. The same for many other branches of physics.


    If the field of HEP becomes stagnant because we don’t have the resources to takle whatever energy level is required to target supersymmetry (assuming it stops being a moving target) then so be it. No need to be delusional or hysteric about it. Invest the hundreds of millions, or billions of € on fields that are not stagnant.
    In 3000 years when we have the technology to probe space at the Planck scale, by all means construct that super duper particle accelerator that will give our descendants insights into quantum gravity and maybe string theory if it isn’t forgotten by then 😉 .

  12. Pravda says:

    Peter, is this article as foolish as it seems to me (“me” being a non-scientist)?

  13. Pingback: Peter Woit warns Michael Shermer not to discredit atheism over multiverse | Uncommon Descent

  14. Peter Woit says:

    Hell’s Kitchen

    I don’t think you’re fair to either Sean or “blog scientists”. There’s a huge range of quality of material put out on blogs from scientists, much of it I think better coverage of science news than you’ll find anywhere else. Yes, most of the best scientists in the world aren’t blogging or letting anyone know what they think, and if you can talk to them privately, they’re your best source of info, but for most people that’s not possible.

    As for Sean, in general I think the content on his blog is accurate and of high quality. To the extent that I see a problem with it, it has to do with the way he writes about very speculative ideas that there are excellent reasons to be highly skeptical about. He is presenting himself as the voice of the scientific establishment, but not always making clear the distinction between when he is talking about settled science where most experts agree, and when he is talking about something highly speculative that some prominent people are enthusiastic about, but which most of their colleagues don’t take seriously (e.g. the multiverse). For a good example of the problem, follow the pingback above to a fanatical intelligent design site to see what kind of trouble Sean’s behavior is creating for the cause of serious science.

  15. Peter Woit says:


    The Register is fond of over-the-top British tabloid ways of expressing things, but I don’t think that’s a particulary inaccurate story. One of the main goals of the LHC is to look for SUSY (“mirror universe theory” I suppose) and extra dimensions. They’re just quoting one LHC physicist about how this is what they’re looking for. One can argue with some details, but the gist of the story is kind of right.

    Would be more accurate of course to have the main point of the story be “LHC not seeing any SUSY or extra dimensions, as most people always expected”, but that’s a hard story to sell to the press.

  16. Jim Clarage says:

    Peter, thanks for pointing out Baggott’s book, and Weinberg’s review. Reading Weinberg’s review reinforced a confusion I’ve always had on the Higgs mechanism and electroweak symmetry breaking: as he says the mechanism gives masses to force carriers (Ws and Z), but is it an extrapolation to say it gives all particles mass (e.g., electron, quark)? In popular writing it seems the LHC Higgs is responsible for all known particle masses.

  17. Peter Woit says:


    What I’d call the “Anderson-Higgs” mechanism discovered in 1963-4 gives masses to gauge fields (the W and Z). These mass terms come from the kinetic energy terms for the Higgs, since in gauge theory these use covariant derivatives involving the gauge field.

    For fermion fields, things are a bit different, and weren’t discussed in the 63-64 papers. There you get masses from the Yukawa interaction terms coupling the fermion field to the Higgs. I’m not sure who first wrote these down, by 1967 Weinberg certainly did, but maybe someone did this earlier.

    As often mentioned, there’s another source of mass: strong coupling in QCD, which provides most of the mass of protons and neutrons.

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