In the years before the LHC start-up, one heavily promoted claim that “yes, string theory can too make predictions, and here’s what it predicts the LHC will see” was based on a class of models known as “F-theory”. Detailed superpartner mass spectra were produced and shown around the world at conferences and departmental colloquia. For an example, take a look at figures 3 and 29 of this paper.
Early LHC results showed that nothing like these mass spectra corresponds to reality. For the latest such results, see Resonaances, which describes new SUSY limits from ATLAS, now wildly out of agreement with the F-theory “predictions”.
At this week’s F-theory Workshop, there seems to have been little acknowledgement of this failure. I didn’t notice either any reference to the fate of the “predictions”, or even an attempt to come up with new, updated ones. The closest I could find was this comment by Michael Dine in a discussion of the state of F-theory phenomenology”:
A lot of us I think are resigned to the idea that maybe there’s supersymmetry and it’s going to look tuned, or maybe there’s not low energy supersymmetry. I think a challenge I’ve always said for string theory is to try and think about theories without supersymmetry and that has proven to be hard. But you know, that’s certainly a direction which maybe we’re being confronted with.
So, the long-standing ideology that supersymmetry stabilizes the weak scale, and seeing its effects will finally give evidence for string theory unification looks like it is crumbling. With this hope gone, string theory unification becomes a completely unpredictive subject, with no hope of connection to experiment. One has an infinite array of mathematically highly complex models one can spend time studying, but it’s hard to characterize doing so as any recognizable form of physical science.
This situation hasn’t slowed down string phenomenologists, who will follow up the F-theory workshop with a summer school for graduate students to train them in the failed techniques of the subject. I have a hard time understanding why any sensible graduate student would want to attend such a thing, or why any responsible advisor would encourage them to do so.