Half Hour to Midnight

Matt Strassler posts here about a recent panel discussion of phenomenologists talking about the implications of the latest results from the LHC. You can listen to the thing for yourself, and see what Matt has to say at his blog, but here are some things that I noticed from watching the discussion:

  • I don’t recall string theory even getting mentioned once. The extent to which string theory is now agreed to be thoroughly irrelevant to LHC physics is kind of striking. The few people like Kane claiming otherwise are being ignored as an embarrassment. If evidence for SUSY or extra dimensions had shown up, this would be very, very different.
  • Arkani-Hamed is probably the dominant personality in this field, and as Matt mentions, he embodies the conventional wisdom of the subject, expressing it at length and with brio. Back in 2005 he was claiming we would know whether SUSY solves the hierarchy problem within a year of LHC turn-on. Somewhat more than a year after LHC turn-on, in February 2011, he was saying that we’d have to wait until 2020. Now he’s putting it differently: it’s the “eleven and a halfth hour” for the idea of SUSY solving the hierarchy problem.

    The only remaining hope for this is that there’s a light stop, which has so far escaped detection, and gluinos just above the current bounds. He sounds willing to bet against this, and is arguing that the idea may soon be toast, to be finally put to bed as results from better stop searches come in over the next few months. If there’s no sign of SUSY in the 2012 data set, it sounds like he’s willing to concede that SUSY can’t be what stabilized the weak scale.

  • On the other hand, he argues that a 125 GeV mass for the Higgs is evidence for SUSY. Here the argument is that such a low-mass Higgs must be an elementary scalar, not the sort of thing you get in technicolor or extra-dimensional models. “SUSY” is here equated with the SM, without comment. I’m not sure what the reason for this is other than the sociological reason that it’s the dominant remaining paradigm for BSM physics, I don’t see a positive scientific argument.

    The 125 GeV value is also described as uncomfortably inconclusive for the idea of SUSY explaining the hierarchy. It’s somewhat too high for this, but not so high as to make it impossible.

  • If the SM continues unvanquished at LHC energies, it sounds like conventional wisdom will move to “it still has to be SUSY, even though our main motivation for SUSY is gone, since we don’t have any better ideas.” Best guess for the SUSY breaking scale will move up to be just high enough to be unobservable at the LHC.
  • Clearly a lot of theorists are looking at the failure of the last quarter century of BSM ideas and trying to figure out what else they can work on. The idea of “back to working on QCD” was repeatedly mentioned. Arkani-Hamed has over the past few years dropped BSM work and moved to a radical speculative program about new ideas for QFT based on a different point of view about amplitudes. One of the speakers jokingly accused him of becoming a mathematician. Maybe that’s where things are going…

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51 Responses to Half Hour to Midnight

  1. Peter Woit says:


    The LHC turn-on ended up being several years later than expected back in 2000, so I think this bet may have been renegotiated to extend the time-line. No cognac purchased by losers yet as far as I know.

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