SUSY in the Hospital?

HCP2012 Higgs results will be announced Wednesday (I’m hearing that CMS tau-tau signal is .7 +/- .5 x the SM value), but interest may focus much more on the strong SUSY exclusions being announced there. So far the LHCb result on B(s)->mu+mu- has been the one getting all the attention, with a BBC News story describing it as “a significant blow to the theory of physics known as supersymmetry”. In the story experimentalist Chris Parkes describes the current situation as “Supersymmetry may not be dead but these latest results have certainly put it into hospital.” John Ellis is having none of this though:

Supporters of supersymmetry, however, such as Prof John Ellis of King’s College London said that the observation is “quite consistent with supersymmetry”.

“In fact,” he said “(it) was actually expected in (some) supersymmetric models. I certainly won’t lose any sleep over the result.”

The story has been picked up by Slashdot, and the Register (which has Supersymmetry takes an arrow to the knee).

The bad news for SUSY out of Kyoto however does not end there. ATLAS and CMS are both coming out with new analyses using this year’s 8 TeV data which significantly expand previous limits on SUSY, getting close to ruling out popular last-ditch efforts to save the theory. For the latest, look at this HCP2012 page, this ongoing Chicago workshop, and CMS results announced here (like this), ATLAS results announced here.

The last ditch effort to save the idea that SUSY solves the so-called hierarchy problem goes under the name of “Natural Supersymmetry”. It involves moving most superpartners to high masses where the LHC can’t see them, keeping only the stop, sbottom, gluinos, and a couple neutralinos at LHC accessible masses. If you look at the bounds given on these masses for instance here, and compare to the latest LHC results, you’ll see that there’s trouble on all fronts for this idea, which is now very close to being essentially ruled out.

Gordon Kane is fighting back against the BBC by going to Lubos Motl’s blog to argue that the LHCb result is no problem for his string theory “predictions”. You see, his “prediction” is now that most superpartners are way beyond what the LHC can see, so not only is the LHCb result not negative for SUSY, but it “adds to the evidence for supersymmetry and for M/string theories”. Kane doesn’t mention any of the other SUSY excluding results coming out this week, or their implications for his “prediction” of the gluino mass. Last year Kane was telling Tommaso Dorigo

I and others expect this decay to tops and bottoms is the signature by which gluinos will be found, with masses well below a TeV

and his slides had a gluino mass prediction of about 600 GeV. Late last year he was arguing that the gluinos would be seen by this past summer. More recently, he’s modified the graph in his slides to move the gluino up to 1 TeV. This week ATLAS reports a new gluino mass limit of 1.24 TeV, so Kane will have to modify his slides yet again.

The combined effect of the bad press and the devastating experimental results on the 30 year old SUSY juggernaut will be interesting to follow. At this point, it is hard to see how one could rationally expect anything positive for SUSY to come out of further analyses of the 7 TeV and 8 TeV data. I suppose many will try and delay acknowledging failure by saying one must wait for the 13 TeV data, which we won’t see until 2015 or so, but I don’t think this is going to convince many people.

Update: Matt Strassler objects to the BBC article, on the grounds that one should not describe what is happening to SUSY in terms of “blows” or it getting hurt. Instead, one should stick to saying it is getting “cornered”, and he agrees that “the cornering of supersymmetry is well underway”. The question this raises though is what happens to SUSY once it is cornered if you object to it getting hurt. I suspect the hope of many SUSY theorists is that even once cornered, SUSY will continue to be well-treated, receiving annual $3 million prizes and being taught to new generations of graduate students.

Update: The Daily Mail covers this, with the non-tabloid-like headline Experts take conflicting opinions as to how far results support the theory of super symmetry. Oliver Buchmueller joins Gordon Kane in the bizarre game of claiming negative results as positive for SUSY, making the argument

‘This is another piece in the puzzle and with it the world appears even more SM-like,’ he said. ‘It supports SUSY, because that is the only theory that can include the Standard Model in a wider concept of New Physics.’

Update: More about this from Matt Strassler, who writes about Theory Killers at the HCP conference. I guess it’s still all right to kill “theories”, as long as SUSY herself doesn’t get hurt.

Update: The rather odd controversy over the BBC story goes on, with Lubos Motl and Matt Strassler continuing to argue that the scientific method implies that SUSY can’t get hurt. I would have thought that it was uncontroversial that if proponents of an idea claimed that it would be vindicated by an experiment, and the experimental result came back negative, that was not good for the idea, but, at least for SUSY, that doesn’t seem to be the case. Yes, SUSY comes in infinite varieties, many of them never testable, but the experimental results shooting down its versions sold as the most well-motivated ones do have implications for its health. I see no reason why one needs to wait for the LHC to examine every possible remote corner of parameter space that it can access before remarking on what has happened.

: It is being pointed out that the BBC story is inaccurate: the LHCb bounds on Bs meson decays that rule out a large chunk of SUSY theory space were already there in March. So, on this front SUSY entered the hospital in March, not this past week. Of course, an even bigger inaccuracy in the BBC story was describing SUSY as an idea that has only encountered serious health problems recently, rather than many years ago…

Update: There’s now a fourth rant from Matt Strassler about the LHCb result, a topic on which he has become a bit of a zealot. The point being made is that SUSY was already so badly injured pre-LHCb that they didn’t make things any worse. It’s quite possible he’s right about this, would be interesting to hear a response from the LHCb people.

Update: A characteristically lucid posting on the topic from Jester: BS and SUSY.

To conclude, you should interpret the LHCb measurement of the Bs→μμ branching fraction as a general, strong bound on theories on new physics coupled to leptons and, in a flavor violating way, to quarks. In the context of SUSY, however, there are far better reasons to believe her dead (flavor, CP, hierarchy problem, direct searches). So one should not view Bs→μμ as the SUSY killer, but as just another handful of earth upon the coffin 😉

Last Updated on

This entry was posted in Experimental HEP News. Bookmark the permalink.

52 Responses to SUSY in the Hospital?

  1. qwerty18 says:

    Hi Peter,
    Could you be a bit more precise about what you call “SUSY” here ? Is it the general idea of supersymmetry ? Some specific SUSY breaking models ? The MSSM ?


  2. chris says:

    Well, the Machiavellian in me tells me to let them pursue SUSY further. All the better for me – less competition on interesting subjects.

  3. John A says:

    These attacks on string theory are giving Sheldon Cooper heartburn.

    Personally I remain completely unimpressed by the constant retreat of SUSY and string theory to energy levels that are currently inaccessible. Any theory that can seriously do that without serious questions or even doubts is moving away from science and into the world of mysticism.

    It’s like the “God of the Gaps” retreat of religious claims in the face of scientific inquiry.

    I suspect that the only way string theory goes away is when the mainstream academic institutions decline to pay for it any more. There needs to be a “Come to God” meeting of theoretical physicists to stop this useless hypothesis draining any more money away from the rest of physics.

  4. Bernhard says:

    I thought Ellis was going to give up on SUSY if it didn’t show up until end of this year? Wouldn’t now be the time to start saying this is becoming more and more likely? Actually I think what he said was for lower luminosity and center-of-mass energy so….

  5. MathPhys says:

    My private prediction is that SUSY will rise from the experimental ashes as a theoretical necessity. The argument will be that you don’t need to see supersymmetry in the lab, but you need to assume that it’s there or your models make no mathematical sense.

    The reasoning will be that if you want to use quantum field theory, you must make sense of the divergences, which requires an embedding in a string theory, which requires supersymmetry.

  6. Roger says:

    As a HEP experimentalist I’m baffled by the extent to which my community pursues SUSY. Its been “around the corner” for as long as I’ve been in the field (coming up to 20 years now).

    As a field, we have long played a scientifically dangerous game of ranking speculative theories we might see. TeV-scale SUSY has regularly topped the league table owing to it (a) providing a DM candidate (b) unifying the couplings and (c) addressing the hierarchy problem. This is the standard stuff that comes on our opening slides when we present our searches. We seem to have forgotten (or just plain ignore) that (a) works so long as we arbitrarily choose a certain LSP and hope that R-parity isn’t violated and that WIMPs can account for dark matter. Similarly (b) works so long as one isn’t particularly choosy about having an exact unification and is willing to buy the argument that no new physics is around for over 10 orders of magnitude of energy which would disturb the running couplings. As for (c) most experimentalists don’t get that this is *the* reason for the theorists liking TeV-scale SUSY. The reason they don’t get it is that they themselves are not particularly convinced by the argument.

    We apply extremely rigorous reasoning in our own world i.e. in the preparation of our results. Its therefore odd that we allow ourselves to be seduced by speculative arguments when it comes to the topics we address.

    As I mentioned at the start, ranking speculative theories is a dangerous game since it eats up finite resources when it comes to data analysis. There may be signatures of new physics sitting in our data which we have missed because of this. We’ll likely catch these signatures anyway sooner or later but it would have been good if the experiments had, at the start, worked out what possible signatures they could observe and studied these without even attempting a ranking as to which are “best motivated” and therefore worthy of more attention.

  7. Bernhard says:


    I agree SUSY is a saturated subject in collaborations, but given 30 years of theoretical propaganda it is difficult not to pursue this to the point of exhaustion. I mean, I am of course afraid sometimes on trigger bias based on SUSY models but for the time being it’ s difficult not to do this. On the theory side that is a different story, but for experiments I think they are doing what they should – massacring SUSY without mercy.

  8. Pete says:

    I agree with Bernhard – just because SUSY does not exist, does not mean we experimentalists should not search for it. This is useful because at some point (if we don’t find it…) theorists ought to go back to the drawing board and come up with a new idea. They probably won’t do that, unless as Bernard says we “massacre it” with experimental results showing it is extremely unlikely to exist.

    Of course the only worry is if that SUSY is completely wrong, we did produce the new physics in the LHC data, but failed to record any of it because we did not know how to look for it.

  9. Roger says:

    Bernhard and Pete
    I’m certainly not proposing that we don’t look for SUSY – part of my own research involves falsifying bits of SUSY parameter space. However, the obsession of SUSY has led to the field of exotics searches becoming lopsided in favour of chasing after models which we consider to be “well motivated”. A well designed set of generic searches would have been more efficient and be as relevant for SUSY as for other approaches (including those we’re not yet able to dream up). There was no need for us to catch the SUSY bug and we should have resisted.

  10. Roger says:

    There is also a more insidious side to this. Whenever I applied for grants, fellowships etc I would emphasise that my work could be used find supersymmetry. To not have played the “topical buzz word” card may well have led to my applications being rejected. I’ve also sat on committees where candidates have been turned down because their proposed searches were considered to be “unpromising”.

    We all pay lip service to the idea that we should be prepared to look for the unexpected and that history tells us to expect surprises etc etc. However, in reality, the field can be very conservative and the SUSY obsession, offering a “safe” research plan with lots of exclusions for legions of interested theorists to play with, is a part of that.

  11. Michael says:

    Hi Roger,

    I appreciate your point very well. But to me it seems a little overstated. Sure there are lots of papers about “SUSY” searches, but most of those searches are able to pick out evidence for New Physics that does not come from Supersymmetry. The advent of the generic models, addressed regularly in the CMS and ATLAS papers, indicates a major shift away from theory-driven searches toward more signature-based searches. (Sorry for bringing in yet more buzz words.) I believe that most of the signatures that we experimentalists can think of are addressed in one way or another, within the constraints imposed by the triggers and event reconstruction. Perhaps I lack imagination, but it is not easy for me to come up with signatures – or perhaps “event topologies” is a better term – that are not covered somewhere, somehow. If you know of searches that someone could do but can’t because the community still invests too much in SUSY, please say what they are. I’m sure many people would be interested. 😉


  12. Eric says:

    In light of the 126 GeV Higgs signal, it appears to me that the most likely scenario involving low-scale supersymmetry is that the superpartners have masses in the range 3-7 TeV. Furthermore, it seems very likely that R-parity is violated at some level. Given this, it is not at all surprising that supersymmetry has not been seen yet at the LHC. However, there is a very good chance that it will turn up in the next run when the LHC will run at somewhat higher energy.

  13. justin says:

    Is Gordon Kane the Karl Rove of superstring theory?

  14. Justin says:

    @Woit: SUSY may be hospitalized, but this raises the question of what should one work on? String theorists have always said that if you don’t like their theory, then what do you have that’s better? I’ve always thought that if someone came up with something viable, then string theory would be far less researched. But, it’s a good question of: if not SUSY, then what? Until someone or some people come up with something that actually works, I think we’ll continue to see many young and old physicists continue to waste their time on this fantasy.

  15. Peter Woit says:


    I don’t disagree that the main reason SUSY continues to get attention is a lack of promising ideas for BSM physics. This is an argument for continuing to do SUSY searches (the discussion between commenters above was quite good about this).

    From the point of view of theorists though, the lack of a better idea is no justification for refusing to admit failure. Intellectual dishonesty is not a likely way forward towards a more promising research program.

  16. emile says:

    I can’t think of a SUSY search being performed right now that should not be done even if one assumes there is no weak-scale SUSY. The problem has been in the past that sometimes parts of phase space were being ignored because MSUGRA did not provide a solution there. But in any case, I think it is important to convey to the wider audience that these searches are not a waste of time. The SUSY searches cast a wide net. Something other than SUSY could be picked up in that net.

    @Mathphys: your theoretical necessity idea should be discussed within the field of philosophy or maybe math, and the associated research should not be supported by physics grants. I have the highest respect for my philosophy colleagues, so I’m not trying to demean the field at all, I just want to make it clear that once you take experimentation out of the picture, it is not science.

  17. Pingback: Ligt SUSY nou wel of niet in het ziekenhuis? | Astroblogs

  18. Justin says:

    @Woit: I agree that SUSY proponents are being dishonest, [deleted]. But, my question is still this: is there any direction a young researcher might pursue if he or she wants to come up with something new?

  19. Igor Khavkine says:

    @Justin, I’m in no way an authoritative voice, but I think the only sensible answer to your question is to look at the data. Look at the data and try to figure out what is not accounted for by what we already know for certain. As far as I understand, every “new physics” discovery came about in this way. An alternative to that is to shift the focus to mathematical aspects. Theoretical physicsits move fast and often leave mathematical gaps in the theories that they are already convinced of by the data. Patching up these gaps does not require any new experiments, only serious thinking. (Incidentally, I’ve personally chosen to adopt the latter approach.)

    Otherwise, sitting in your office and trying to imagine what new physics might be like is unlikely to get you very far, at least scientifically. I wouldn’t be able to judge the effect on your career path.

  20. Peter Woit says:

    Justin + Igor Khavkine,

    I’d rather people stick to the topic of the new SUSY results and not try and start an open discussion of “what should theorists work on”. As I keep pointing out, this isn’t a general physics discussion board…

  21. Shantanu says:

    could you comment on effect of lack of evidence for SUSY (so far) on GUT based
    theories and if there has been any discussion of this apart from Misha Shifman’s proceedings
    Many Thanks

  22. Peter Woit says:


    The LHC results don’t have much to say one way or another about GUTs (I don’t think GUTs make any testable predictions about LHC physics). One of the standard arguments given for SUSY is that the running of the U(1), SU(2) and SU(3) coupling constants in SUSY theories causes them to come together more accurately at the GUT scale than if you stick to the Standard Model, allowing a simple construction of SU(5), SO(10) and other SUSY GUTs. One problem with this is that the bounds on proton decay are starting to get significantly in conflict with this idea. Another is that it also requires believing in a “desert” of no new physics that affects the running of coupling constants between the TeV and GUT scales. For these reasons, this always seemed to me a rather weak argument for SUSY (although arguably the strongest one). That the arguments for SUSY all turn out to be quite weak, and that the LHC sees no evidence for it is a quite consistent situation.

  23. tulpoeid says:

    “Without it, you would have smart people saying smart things and stupid people saying stupid things. But for smart people to say stupid things, that takes susy.”

  24. vmarko says:


    The reasoning will be that if you want to use quantum field theory, you must make sense of the divergences, which requires an embedding in a string theory, which requires supersymmetry.

    Making sense of divergences has nothing to do with string theory, nor with supersymmetry. The Standard Model is renormalizable as it stands. The real theoretical issue that might serve as motivation for both SUSY and strings is the fact that gravity is perturbatively nonrenormalizable. And that problem can be attacked in many ways, SUSY/strings being only one of many possibilities.

    So, neither SUSY nor string theory can ever be considered a theoretical necessity, unless they are backed up by experimental data. And that somehow is just not happening, as we can see…

  25. Pingback: Is Physics in Trouble? Results Confine Supersymmetry | Fleeing Nergal, Seeking Stars

  26. fuzzy says:

    “I would be more inclined to trust lawyers claiming for justice if I could believe that they gain nothing by doing that.”

  27. King Ray says:

    Perhaps the only way to save SUSY is mouth-to-mouthino resuscitation . . .

  28. Pingback: Is there any particle physics beyond the standard model? « Mostly physics

  29. MathPhys says:


    Okay, let’s say that one requires “renormalizability, even in the presence of quantum gravity”.

  30. Pingback: Assorted links

  31. P says:

    Hi Peter,

    I’m confused by some of your statements and criticisms.

    Which of the “infinite varieties” of SUSY that you mentioned are “never testable”?

    And how many of the $3 million recipients work regularly on the types of SUSY theories you discuss on this blog, rather than the many other types?


  32. Peter Woit says:


    Neither of those statements was intended as a crucial part of a serious argument about anything, but I think “never testable” pretty well describes SUSY theories with high enough SUSY breaking scales. Such theories seem to be more popular now that it is becoming clear the SUSY breaking scale can’t be low enough to solve the hierarchy problem.

    As for $3 million prize winners, my comment was about future ones. The Milner prize is rather explicitly aimed at fundamental research not vindicated by experiment, but considered important by the leaders of the HEP theory community. If you’re someone with major contributions to SUSY research as your main professional accomplishment, your shot at the $3 million requires that the “SUSY is dead” meme not get traction among your colleagues. We’ll see what happens, but the lack of any successful BSM ideas coupled with yearly $3 million prizes for fundamental research targeted at HEP theorists may mean you’ll have a yearly competition to be seen as the person who had the least bad unsuccessful but high-profile idea, with SUSY part of the mix.

  33. P says:

    Hi Peter,

    Okay, I agree with your clarified sentiment regarding testability – “never testable” really means “never testable if we don’t build sufficiently big colliders.”

    Regarding the hierarchy problem, there’s a sliding scale, right? Even with O(TeV) SUSY breaking, there was still the little hierarchy problem. LHC might put bounds at O(10TeV) SUSY breaking, which we might call the “even bigger little hierarchy problem.” I know you don’t agree with the premise, but with this premise its not quite right to say that LHC will make SUSY unable to solve the hierarchy.

    Regarding Milner prizes – I guess, but the “SUSY is dead” meme, if it gains traction, will only do so in the realm of N=1 BSM physics with low SUSY breaking scale for the sake of solving the hierarchy problem. Nearly all of the winners who won the prize have significant contributions to other areas of supersymmetric field theories, and the success of this work and future work on non-BSM SUSY stands firm regardless of the conclusions of the LHC. This is an important distinction to make, I think.

    In any case, I agree with you regarding this prize and SUSY extensions of the SM. However, it’s hard to imagine someone getting the prize “aimed at fundamental research” for such work (at least, as their primary contribution) without experimental vindication.

  34. Bernhard says:


    Logically speaking is a sliding scale yes, but why should anyone believe this will happen? So, it is not a matter logical possibility, it is a problem with the motivations for SUSY becoming increasingly weaker without its proponents admitting it for some reason. Look what happened with R-parity. Before the LHC results R-parity violating SUSY was ratter unpopular because it is required for the “explanation of dark matter”, now suddenly R-parity is old news and this particular motivation was just thrown under the bus. The biggest motivation is by far naturalness and as you correctly point out the little hierarchy problem is getting bigger. It is a logical possibility of course the SUSY is there with very heavy superpartners but the motivations used for that being a likely result are clearly being weakened by experiment. One could think this would lead legions of young and creative theorists to think “probably the answer is somewhere else” and show new exciting possible solutions, but instead what we see are theorists claiming SUSY suffered no scratch and this is simply plain wrong.

  35. P says:

    Hi Bernhard,

    Thanks for the reply.

    I agree with most of the things you say. Certain low energy SUSY models are definitely being cornered / “suffering a scratch”, and as these theories are cornered more and more some of the motivations for BSM SUSY particle physics begin to go out the door, on a sliding scale as we have agreed.

    Re: “the answer is somewhere else” . . . the answer to what? The hierarchy problem? BSM physics in general? People have been looking at non-SUSY extensions of the SM and also non-SUSY solutions to the hierarchy problem for years. I don’t disagree that young particle theorists should be open minded, but am only pointing out that other many other possibilities have already been considered. Data is coming in and is constraining both SUSY and non-SUSY possibilities. Very exciting!


  36. Bernhard says:


    I agree…

  37. Saw this via “Marginal Revolution”. What about the hypothesis expressed in Leonard Susskind’s The Cosmic Landscape that SUSY holds only in the “dead” ground-state of the meta-stable sequence? Is that being “cornered” too, or only whether SUSY holds in our world (where we have Lambda > 0 etc.)? In any event, my impression from the book was definitely not to expect any our-world experiments upholding SUSY.

  38. P says:


    Peter would probably object to this thread going down the direction you’ve suggested, since it brings on a whole host of other issues – but it suffices to say that (based on context) the SUSY you bring up is a reference to a SUSY vacuum in a landscape of metastable SUSY breaking vacua. This is something different: our world is definitely NOT in a SUSY vacuum, and moreover this isn’t really the context in which SUSY is being tested at LHC.

    — P

  39. Peter Woit says:


    At one point Susskind had hopes that you could make statistical arguments based on the Landscape, such that you might find it was statistically probably that SUSY would be seen at LHC energies (or that it was statistically unlikely). Turns out this doesn’t work, the Landscape can’t be used to say anything about this one way or the other (or about anything else, this was supposed to be the most likely thing that could be predicted this way). So, landscapeologists like Susskind would happily claim SUSY as evidence for string theory if it appears, also claim it is no problem for string theory if it doesn’t.

    I wrote about Susskind’s book here

    in particular:

    Susskind talks about the LHC and the question of whether the fine-tuning problem of the Higgs mass will be resolved by supersymmetry or is anthropic. He acknowledges that, based on Landscape arguments:

    “My original guess was that supersymmetry was not favored, and I said so in print. But I have changed my mind — twice — and probably not for the last time.”

  40. fuzzy says:

    i think that when we call “susy” that stuff we use an improper name. (btw, do you know who created this acronym? i heard it was john ellis, but is it true or just a rumor?) i think that a much more apt acronym would be “seotsmjatewsawrpifabmtanfal” =supersymmetric extension of the standard model just above the electroweak scale and with r-parity imposed forcefully, advocated by many theorists and not found at lhc. i can admit that the name “seotsmjatewsawrpifabmtanfal” is not as appealing as “susy”, but it is honest: indeed there is no convincing theoretical reason why the supersymmetric extension should be at the electroweak scale (the scale of mass is not predicted) or why r parity should be conserved (gauge invariance would suggest that it isn’t). furthermore, if we will find something like that at lhc, we will remove the “n”, the acronym will reduce to “seotsmjatewsawrpifabmtafal”, and its appeal will grow in an adequate manner.

  41. John Adams says:

    Rather new to all this, I’m afraid. But I do have a simple question. If supersymmetry is not found, or even proven incompatible with new evidence, would that in itself kill off superstring theory and all its close relations – M theory and the like – or have these theories developed in such a way that they could survive the death of supersymmetry?

  42. Peter Woit says:

    John Adams,
    Superstring theory/M-theory unification predicts essentially nothing (I wrote a book explaining more about this…), so you can’t kill the idea with experiment. There was a day when string theorists would often object to this claim by pointing to SUSY, but not these days. However, if SUSY is found, I can predict that you definitely will hear a lot again about how this is evidence for string theory…

  43. John Adams says:


    Thanks for the reply. I’ve ordered and am currently awaiting the arrival of your book. From what I can gather string theory makes essentially no predictions, so I understand your point. And I certainly understand that string theorists would be doing somersaults if supersymmetry was found. But my point is does string/M theory absolutely *require* supersymmetry. What would happen to string/M theory if it were demonstrated scientifically that supersymmetry was impossible.

    Let’s take an outlandish example to make my point. Imagine that tomorrow Ed Witten discovered beyond any shred of doubt that an overlooked part of supersymmetry demanded that the speed of light was minus 1 metre per second. We can all accept that then SUSY would be dead. But what would it mean for string/M theory. Would they fall too, or have they been developed the last couple of decades in ways such that they could bear SUSY’s death?

  44. Shantanu says:

    John, This has been discussed several times on this forum. string theory is consistent with everything, including mutually opposite ansatzs

  45. Peter Woit says:

    John Adams,

    The problem with supersymmetry is that it must be a broken symmetry, and the problem with string theory is that, to the extent it requires supersymmetry, it says nothing about the breaking scale. It could be at the Planck scale, completely irrelevant to any conceivable observation.

  46. P says:


    Here’s a bit more precision. String theory does NOT require spacetime supersymmetry, but broad classes of compactifications do give rise to N=1 supersymmetry in four dimensions.

    Regarding the LHC and experiments, the question then is the SCALE of supersymmetry breaking, as Peter points out. It’s too vague (and one could argue incorrect) to say that string theory says nothing about the breaking scale.

    The key point is that, as in quantum field theory, is that one has to study the vacuum state. Individual string vacua make very concrete predictions – I’d be happy to tell you about them and cite papers – including the SUSY breaking scale, if it is broken at all. In most vacua the SUSY breaking scale is high, “irrelevant to any conceivable observation”, as Peter points out.

    It’s too vage, misleading, and fundamentally incorrect to make the blanket statement “string theory does not make predictions.” The problem of predictions in string theory is NOT that individual vacuum solutions don’t make low energy real-world predictions, but instead that there are an extremely large number of vacuum states. This observation applies to predictions about the SUSY breaking scale (hence Peter’s objection), and also predictions about the low energy gauge theory, for example.

  47. H Luce says: neatly summarizes the response of the established string theory community to any challenges… never mind that their hypotheses are untestable.

  48. john McAllison says:


    I think you’re letting yourself down a little by describing Matt’s update on SUSY as a “rant”; I’d describe it as a fourth installment. He’s just presenting his side to the argument in a calm rational way and I’d hate to see you lower your current high standards of fairness compared to those of others I can mention. It’s impressive the way you link to Matt’s and, unbelievably, Lubos’s blog for example.

  49. Peter Woit says:

    John McAllison,

    Perhaps you should take that description as somewhat tongue in cheek… Any one who cares though is encouraged of course to follow the links and see what Matt and his commenters have to say. The whole SUSY business seems to me to have led to some rather odd behavior among physicists, but others can judge for themselves.

  50. zevans23 says:

    BBC Radio 4’s “Material World” weekly radio magazine has a good high-level interview with Dr Tara Shears, and does convey the “not even wrong” message well. Essentially the conclusion is “wait for higher energy.”

    Podcast (available to all countries!) here – you want Thu 15 Nov.

Comments are closed.