In the years leading up to the LHC, string phenomenologists were vocal about their hopes to use string theory to make predictions about what the LHC would see, despite a history of a quarter-century of failure on the prediction front. For example, in late 2007 Michael Dine was writing in Physics Today:
A few years ago, there seemed little hope that string theory could make definitive statements about the physics of the LHC. The development of the landscape has radically altered that situation. An optimist can hope that theorists will soon understand enough about the landscape and its statistics to say that supersymmetry or large extra dimensions or technicolor will emerge as a prediction and to specify some detailed features.
The main target for a landscape prediction has always been what appears to be the simplest possible question about BSM physics that the landscape could hope to address: is the supersymmetry breaking scale likely to be high (GUT/Planck scale) or low (electroweak scale)? By the time the LHC data started to arrive (showing no supersymmetry), these hopes for a landscape prediction had failed, as it became clear there was no way to get a clear answer about this (or any other question…) out of landscapeology. Landscape proponents have still not given up though, with Michael Douglas yesterday putting out a survey of work on the SUSY question, The string landscape and low energy supersymmetry. He has no string theory predictions, but he has a (very tentative) prediction about a (sort of) prediction:
I am going to go out on a limb and argue that
String/M theory will predict that our universe has supersymmetry, broken at the 30 − 100 TeV scale. If at the lower values, we may see gluinos at LHC, while if at the higher values, it will be very hard to see any evidence for supersymmetry.
This is a somewhat pessimistic claim which far outruns our ability to actually make predictions from string theory. Nevertheless I am going to set out the argument, fully realizing that many of the assumptions as well as the supporting evidence might not stand the test of time.
As for the time scale and reliability of this prediction of a prediction, he writes:
My guess at present is that twenty years or more will be needed, taking us beyond the LHC era. Even then, it is likely that such predictions would depend on hypotheses about quantum cosmology which could not be directly tested and might admit alternatives. It is entirely reasonable that sceptics of the landscape should reject this entire direction and look for other ways to understand string theory, or for other theories of quantum gravity. At present we do not know enough to be confident that they are wrong. Nevertheless the evidence at hand leads me to think that they are wrong and that this difficult path must be explored.
So, optimistically, if all goes well, long after the LHC is shut down, maybe we’ll see a landscape prediction about whether the LHC should have seen SUSY. This prediction will depend upon assumptions about quantum cosmology that can’t be tested, so if it disagrees with what the LHC saw, that won’t falsify the landscape anyway.
Meanwhile, Gordy Kane is promoting the idea that string theory already has made a prediction: a 125 GeV Higgs mass, spectacularly in agreement with the latest data, and gluinos detected “by summer”, “with masses around a TeV, maybe less” (see here). He’s giving a talk today at the Simons Center with the title “String theory, the real world, and the prediction of the Higgs boson mass”. As far as I can tell though, no one except possibly his collaborators believes him. At a public talk on the Higgs recently here at Columbia, Brian Greene was very skeptical, joking that if the LHC had seen something at 142 GeV, that would be Kane’s “prediction” (for more about this, see Lubos’s outraged coverage here).
Matt Strassler recently weighed in on the Kane prediction, which so outraged him that he has stripped Kane of his professional title. Matt is careful to put “Professor” before his own name and those of others who deserve the title, but Kane is now “Mr. Kane”:
The level of garbage and propaganda surrounding the Higgs is getting pretty ridiculous.
You realize, yes, that by August 2011 the window for the Standard Model Higgs was down to 115 to 140 GeV, right? So your chances of getting within 5 GeV of the right answer is 15%. Many theories before Mr. Kane predicted a range that included 125 also. I’m completely unimpressed both by the science and the propaganda. Most of my friends who are experts in compactification (which Kane is not — he relies on one of his collaborators — and I am not an expert either) are not convinced of the assumptions on which they base their arguments. It all sounds good. But is it really? I’ve heard lots of arguments that sounded good over the years… and most of them are now known to be wrong. None of them are known to be right.
Do not judge science on the ability of the scientist (who wants his or her Nobel prize and is trying his or her best to convince you) to present a compelling argument. A great salesperson can create a terrific argument; a great physicist does not need one.
So, Kane seems to be finding that his “string theory prediction of the Higgs mass” is being met with scorn, from all segments of the particle theory community. I’m curious what has happened to his paper from early December, which I’d guess was intended for PRL, but has yet to appear. He has about a month and a half for the gluinos to show up “before summer” and vindicate his “prediction”.
The Strassler comment was at a useful posting about the state of SUSY searches (see here). Matt’s time estimate for how long it will take the LHC to rule out SUSY: “This will take a while, probably a decade.” A more mainstream time estimate might be that it has already happened. For Tommaso Dorigo’s take on this, see SUSY and the Silence of the (Roasted) Lamb.
Starting tomorrow Brookhaven will host a workshop on the state of SUSY topic. For latest developments, look at the slides as they appear here.
Update: The video for Kane’s talk at the Simons Center is now available. Instead of gluinos “by summer”, he’s now changed his tune, and he expects “discovery during 2012” (if the expected luminosity goals are met). The mass of the things has moved up from less than about 1 TeV to less than about 1.3 TeV.
Update: The Kane et al. paper with the Higgs mass “prediction” has just appeared at Phys. Rev. D. The preprint went to the arXiv on December 5, the Phys. Rev. D submission date is February 13. One guess would be that this more than two month delay might be due to the paper being rejected (or a referee insisting on the “string theory prediction” nonsense being removed) wherever it was first submitted, perhaps PRL.
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