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.