Alok Jha has a piece in the Guardian yesterday about the failure to find SUSY. His conclusion I think gets the current situation right:

Or, as many physicists are now beginning to think, it could be that the venerable theory is wrong, and we do not, after all, live in a supersymmetric universe.

An interesting aspect of the article is that Jha asks some SUSY enthusiasts about when they will give up if no evidence for SUSY appears:

[Ben] Allanach says he will wait until the LHC has spent a year or so collecting data from its high-energy runs from 2015. And if no particles turn up during that time? “Then what you can say is there’s unlikely to be a discovery of supersymmetry at Cern in the foreseeable future,” he says.

Allanach has been at this for about 20 years, and here’s what he has to say about the prospect of failure:

If the worst happens, and supersymmetry does not show itself at the LHC, Allanach says it will be a wrench to have to go and work on something else. “I’ll feel a sense of loss over the excitement of the discovery. I still feel that excitement and I can imagine it, six months into the running at 14TeV and then some bumps appearing in the data and getting very excited and getting stuck in. It’s the loss of that that would affect me, emotionally.”

John Ellis has been in the SUSY business even longer, for 30 years or so and he’s not giving up:

Ellis, though confident that he will be vindicated, is philosophical about the potential failure of a theory that he, and thousands of other physicists, have worked on for their entire careers.

“It’s better to have loved and lost than not to have loved at all,” he says. “Obviously we theorists working on supersymmetry are playing for big stakes. We’re talking about dark matter, the origins of mass scales in physics, unifying the fundamental forces. You have to be realistic: if you are playing for big stakes, very possibly you’re not going to win.”

But, just because you’re not going to win, that doesn’t mean you have to ever admit that you lost:

John Ellis, a particle theorist at Cern and King’s College London, has been working on supersymmetry for more than 30 years, and is optimistic that the collider will find the evidence he has been waiting for. But when would he give up? “After you’ve run the LHC for another 10 years or more and explored lots of parameter space and you still haven’t found supersymmetry at that stage, I’ll probably be retired. It’s often said that it’s not theories that die, it’s theorists that die.”

There may be a generational dividing line somewhere in the age distribution of theorists, with those above a certain age likely to make the calculation that, no matter how bad things get for SUSY and string theory unification, it’s better to go to the grave without admitting defeat. The LHC will be in operation until 2030 or so, and you can always start arguing that 100 TeV will be needed to see SUSY (see here), ensuring that giving up won’t ever be necessary except for those now still wet behind the ears.

For another journalist’s take on the state of SUSY, this one Columbia-centric and featuring me as skeptic, see here.

Urs,

your argument is correct, but you have to admit it is a little bit like parents who are proud that their little kid already knows complex numbers – because it can count to three. Yes, 1, 2 and 3 are complex numbers, but …

Giotis,

It’s actually incorrect to say that the only way to extend the Poincare group is through SUSY. For one thing the Coleman Mandula theorem deals with S-Matrices, which assumes the existence of asymptotic states that don’t interact with each other. You can do away with this assumption if you consider a conformal field theory. So there are three extensions of the Poincare group: 1)Adding conformal transformations, 2) Adding SUSY generators, or 3)Both.

Another assumption is that we live in flat Minkowski space. If you consider DeSitter or AdS space another exception: Vasiliev theory. There you have an infinite number of higher spin fields.

Although I agree with you that the fact that in flat space, when there is a mass gap and the S matrices are nontrivial the only nontrivial extension of the Poincare group is through SUSY is a compelling argument, you do need to remember the assumptions and other exceptions (besides SUSY) to the Coleman-Mandula theorem.

David M,

I’m not sure what you are trying to convey here. Even for massless fields and Conformal field theories the most general symmetries you could have are still Supersymmetric i.e. the Superconformal algebra. And Vasiliev’s Higher Spin superalgebras are Supesymmetric ones too.

So what’s your point?

Giotis,

You wrote: The only way to extend Poincare algebra and still respect Lorentz invariance is the super-Poincare algebra.

My point is that this is not true, there are other extensions that work if you relax the assumptions. Yes the maximal extension of the Poincare algebra will include SUSY, but now we’ve switched from the question of what’s the maximal extension of the algebra (which will include SUSY) to a minimal nontrivial extension (which does not necessarily include SUSY). And we know conformal symmetry is not an exact symmetry of nature because we have mass (although at high energies its a good approximate symmetry), so theres no reason to assume SUSY will be an exact symmetry either just because its allowed.

That’s not to say these subjects aren’t worth studying. CFTs and SUSY gauge theories are important objects to study to understand QFTs and can appear in condensed matter systems (http://arxiv.org/abs/1009.5127 Sung Sik Lee has done work on emergent SUSY), but until its seen an experiment you can’t be 100% certain its a symmetry of particle physics.

When you think of why someone will never give up an idea or object, you have to step out from the idea or the object, and consider what that idea or object means to that individual. It is more than physics, more than career, but it is psychology. It is completely personal. I don’t see SUSY (or string theory) dying in next 10 years.

Sadly, the most successful people who are flexible, accept new information as it is, and understand what that do not understand.

“It is not the strongest species that survive, but the one that is most adaptable to change.”

“To know is to know that you know nothing. That is the meaning of true knowledge.”

“Facts change, and I change my mind. Will you sir?

I guess a quote from Will Rogers seems appropriate here.

“It ain’t what you don’t know that counts. It’s what you know that ain’t so.”

Ran across this in the book “A Mathematician Reads the Newspaper” by John Allen Paulos.

Trying to balance the opinions of experts is a rather tricky business, particularly for those of us looking at HEP-EX/TH from outside. I know Bayesian methods are used in the estimation of parameters in particular physics so was hoping that some group had run a model selection test between the SM and a version of SUSY.

With a little digging in the arxiv, I came across this paper with the provocative title “Should we still believe in constrained supersymmetry?” The conclusion of

NOis presented in a rather circumspect and wordy fashion, despite the analysis being pretty definitive.Has anyone else seen any similar studies testing the SM vs MSSM or some other slice of the SUSY space? I cannot imagine models with a wider range of free parameters would fair any better, their posterior probabilities being dragged down by the increased Occam factors. Is it worth another two decades of work on SUSY, particularly as the models get more contrived as the simplest ones are ruled out? I guess that’s for HEP internally to decide.

Many former string researchers now seem to have refocused on holographic duality. I wonder if this new article by Don Marolf is relevant to the “never give up” issue:

“A defining feature of holographic dualities is that, along with the bulk equations of motion, boundary correlators at any given time t determine those of observables deep in the bulk. We argue that this property emerges from the bulk gravitational Gauss law together with bulk quantum entanglement as embodied in the Reeh-Schlieder theorem. Stringy bulk degrees of freedom are not required and play little role even when they exist…”

from *Holography without strings?* http://arxiv.org/abs/1308.1977

Historical comment:

In your March, 2004 blog you quoted from a talk by David Gross, and said “He then went on to claim that in 3-4 years there will be a headline in the New York Times about the discovery of supersymmetry at the LHC.”

Not so.

Well you have to give him some credit at least; it was a falsifiable prediction…