The title of the posting is that of Nima Arkani-Hamed’s public lecture last week at the IAS, with the spelling that of the title at the beginning of the video (available here, lower resolution version here).
The bulk of the talk is devoted to expounding the idea that the central problems of fundamental physics are two hierarchy problems, that of the CC (why isn’t it at the Planck scale?) and that of the Higgs mass (why isn’t it also at the Planck scale?). Given that we don’t understand quantum gravity, and don’t know that the Higgs phenomenon is due to an elementary scalar, it’s not clear to me that these are yet real problems. In any case, Arkani-Hamed gives the anthropic multiverse argument for the CC problem, and claims that if the LHC doesn’t see supersymmetry or large extra dimensions, then we’re stuck with the anthropic multiverse argument also for the electroweak scale.
The LHC only puts in an appearance in the last fifteen minutes of an hour and a half talk. Back in 2005 (see his talk at Strings 2005) Arkani-Hamed claimed that we would know whether supersymmetry solves the hierarchy problem within a year or so of first collisions at the LHC (then scheduled for summer 2007). Now that initial results from the LHC are in, showing no evidence of supersymmetry, his estimate is:
We’re going to have answers one way or another to this question on the time scale of 2020.
One of his slides estimates production of 1 squark/minute given 1 billion collisions/sec, which would mean about 50 squarks already produced in each detector. While it’s true that the LHC won’t be running at full energy until 2014, no explanation is given for why we need to wait until 2020 to find out about supersymmetry. Back in 2005, before the machine was turned on, enthusiastic predictions of quick results were being made. Now that the data is coming in, the story seems to have changed.
Update: Nature News has a new article up by Geoff Brumfiel: Beautiful theory collides with smashing particle data (also available here). While Arkani-Hamed is arguing that one will have to wait until 2020 (the sLHC perhaps?) before knowing whether supersymmetry is at LHC energies, John Ellis appears willing to give up much earlier, maybe the end of next year:
“I’m wouldn’t say I’m concerned,” says John Ellis, a theorist at CERN, Europe’s particle-physics lab near Geneva, who has worked on supersymmetry for decades. He says that he will wait until the end of 2012–once more runs at high energy have been completed–before abandoning SUSY. Falkowski, a long-time critic of the theory, thinks that the lack of detections already suggest that SUSY is dead.
“Privately, a lot of people think that the situation is not good for SUSY,” says Alessandro Strumia, a theorist at the University of Pisa in Italy, who recently produced a paper about the impact of the LHC’s latest results on the fine-tuning problem. “This is a big political issue in our field,” he adds. “For some great physicists, it is the difference between getting a Nobel prize and admitting they spent their lives on the wrong track.” Ellis agrees: “I’ve been working on it for almost 30 years now, and I can imagine that some people might get a little bit nervous.”
The article ends with a very sensible quote from experimentalist Chris Lester, who evidently doesn’t share Arkani-Hamed’s view that it’s SUSY or the Multiverse:
“Plenty of things will change if we fail to discover SUSY,” says Lester. Theoretical physicists will have to go back to the drawing board and find an alternative way to solve the problems with the standard model. That’s not necessarily a bad thing, he adds: “For particle physics as a whole it will be really exciting.”
Update: It seems that the video files have been temporarily removed, presumably for editing. I fear that some poor tech person is having a bad morning…
Update: New video files with typo fixed are now available.
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