# The State of SUSY

Results putting new limits on SUSY based on the entire first run of the LHC are starting to emerge (see for example this from CMS) with more likely at Moriond next week. Since one is dealing with a theory with a large number of parameters, these are hard to characterize in a simple way. One thing to focus on is the limits on gluinos, since just about every popular version of SUSY says these should be about the easiest thing for the LHC to see. Very roughly, the Tevatron was able to set typical limits of about 300 GeV on such things, and the LHC at 8 TeV (4 times the Tevatron) is now giving limits around 4 times higher, 1.2 TeV. This is not likely to change much for the next few years until after the LHC comes back at 13 TeV in 2015. One can with some confidence predict that the gluino mass limit will then go up to about (13/8)*1.2 TeV or around 2 TeV, maybe a bit more in years after that with a high-luminosity LHC. Farther out in time, the next machine under discussion that could raise the limit is the HE-LHC, at 32 TeV, giving limits around 5 TeV. The time scale for this though is something like 2030-40, even assuming such a project ever were to get funded. I suspect the right characterization of that project might be “not in my lifetime”.

There is a new paper out claiming to see evidence of a gluino in the data around 1000-1100 GeV. The same authors (see here), have been claiming to see such gluinos since the early LHC data, first at around 7-800 GeV, with a mass getting higher with each round of new data and higher mass limits.

Few are likely to pay attention to this, but what is getting taken much more seriously is the case that Nima Arkani-Hamed has been vigorously making recently (see for example his talk at the Higgs Symposium). Arkani-Hamed is now by far the most influential theorist in this area, with slides from his latest talks often appearing in many other people’s presentations, functioning as the embodiment of the conventional wisdom of the field. He also is the only phenomenologist with a $3 million Fundamental Physics prize, awarded for his work on models that have had great influence, although zero success experimentally. One of these, split supersymmetry, is what he is now promoting as the explanation for the negative LHC results. In this model, which he developed with Savas Dimopoulos back in 2004, the main argument for SUSY, the hierarchy argument, gets abandoned in favor of anthropics. The Higgs mass and the electroweak scale are what they are not because of SUSY, but because otherwise physics would be different and we wouldn’t be here. Once one abandons the hierarchy argument, the remaining arguments for SUSY are extremely weak (I’ll try and explain these in more detail in a separate posting), but for some reason Arkani-Hamed still thinks the idea is worth promoting and that vindication for his$3 million may yet be had.

Split SUSY works by moving all scalar superpartners up to unobservably high energies, but a few particles including the gluino are supposed to be at potentially observable masses. Back in 2004, Arkani-Hamed and Dimopoulos were hopeful about the possibilities for the LHC seeing a split SUSY gluino, writing:

However, at peak luminosity of 30 fb-1 per year, the LHC may well be a gluino factory producing roughly a gluino per second(for m_g ∼ 300 GeV).

These hopes have now been dashed, and at the Higgs symposium talk, illustrative spectra show gluino masses at 2.1 and 2.3 TeV (this may just be because that’s about the limit of what the LHC could see). Arkani-Hamed and co-authors have a recent paper out discussing Simply Unnatural Supersymmetry, i.e. “the simplest picture of the the world arising from fine-tuned supersymmetric theories”. Here calculations are done for gluino masses ranging from 1.5 to 15 TeV, and the story is that we’ll have to be lucky to get any experimental evidence for this model. They end with:

If Nature has indeed chosen the path of un-natural simplicity, we will have to hope that she will be kind enough to let us discover this by giving us a spectrum with electroweak-inos lighter than ∼ 300 GeV or gluinos lighter than ∼ 3 TeV.

So, the current state of the conventional wisdom about SUSY from its most influential proponent is pretty much the following. It’s still the thing to try and sell to the public as the best bet for the future of physics, but the hierarchy argument is gone, and at a fundamental level it’s anthropics, the landscape and the multiverse. He’s pretty much given up hope of ever getting any experimental evidence for this, other than the outside possibility of maybe the gluino mass being just low enough to be visible in rare LHC events late in the decade.

The interesting question about all this I think is a sociological one: will this untestable and rather ugly theory based on anthropic reasoning become widely seen as the “best hope” for fundamental particle theory? In a post-LHC world where mankind has abandoned the high-energy frontier, will the conventional wisdom of the textbooks be that SUSY and those gluinos must be there, but unfortunately happen to be just out of reach?

Update: For a survey article that just came out this evening, which tries to show that the main argument for SUSY (the hierarchy problem) is not quite dead yet, see here.

Update: New Scientist has a special section this week about “Crunch time for physics” (unfortunately mostly behind a paywall). On SUSY, Frank Wilczek is still a believer, based on the renormalization group calculation he was a co-author of back in 1981. If no SUSY turns up at the next LHC run though, even he will throw in the towel:

I cannot believe this success is an accident. But in science faith is a means, not an end. Supersymmetry predicts new particles, with characteristic properties, that will come into view as the LHC operates at higher energy and intensity. The theory will soon undergo a trial by fire. It will yield gold – or go up in smoke.

He has a bet with Garrett Lisi that superparticles will be detected by July 8, 2015.

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### 65 Responses to The State of SUSY

1. Pi says:

Peter,
Many thanks for posting this.
I don’t think, if SUSY doesn’t show up at the LHC, physicist can easily persuade governments to build another gigantic collider. 2030-2040 is too optimistic I think.
So what will HEP theorists do 1)if SUSY doesn’t show up 2) in the meantime for another collider?

2. Mitchell Porter says:

The structure and the parameters of the standard model will still need explaining. And if anyone ever manages to hit on the right explanation, presumably it will predict the next decimal place in the parameters. So experiment won’t be completely dead, even if there’s nothing beyond the Higgs.

3. John says:

HEP theorists will be fine. Maybe you’re wondering about phenomenologists? They’ll just keep doing what they’ve been doing for the past decade or so, up to and including the LHC period. Invent various random scenarios of zero value. The only thing the LHC did was confirm what we already pretty much knew. Actually it did two things. It also artificially boosted the number of pheno hires, for a “just in case something shows up we need many monkeys to figure it out” scenario.

Since the LHC taught us nothing new, I’m not sure why we should be so eager to build yet another one. There’s plenty of other stuff do anyway. Also things like dark matter detectors are much cheaper and there are actually better motivations behind those. We actually expect dark matter, which we know nothing about. We aren’t however expecting anything at the LHC, it’s all just “spray and pray”.

4. M. Wang says:

It had been known since before the Great Depression that, in aggregate, stock analysts’ predictions produce negative risk-adjusted returns, but thousands of people still make it a living to this day, some being paid 7-digit salaries. It is even considered a serious offense to discuss their track records in industry gatherings.

By the 1990’s, solid statistics had proven beyond doubts that mutual fund managers as a whole added negative values after fees, but the industry continued to grow. It now manages assets well in excess of the US GDP.

As of last month, the latest statistics on hedge funds also showed a negative overall return after fees in aggregate. Yet, your university may have to cut hiring further next year because its endowment fund loses a few more billions in various hedge funds.

The point of my long-winded examples is that, in a complex society, there is plenty of room for BS-artists to prosper as a group or even industry. My bet is that the likes of Brian Greene and Lisa Randall will continue to sell plenty of books, be invited to guest-star in TV shows and give inspirational speeches to young students in science. Of course, the dark matter may come to rescue HEP from ignominious heat death, but what if it doesn’t? Is there any reason why dark matter has to be WIMP? Does a WIMP have to have a signal measurable within the next 20 years? What if nothing shows up?

5. Umesh says:

Why do you have to keep trashing genuine attempts at explaining nature in a rather negative and totally un-constructive fashion?

6. Shantanu says:

Peter (or others), is there any current serious attempt to link SUSY models to neutrino masses/mixings etc? Way back in 1998 when first non-0 evidence for neutrino mass was found, P. Ramond claimed its evidence for low energy SUSY.

7. Yatima says:

@John

“The only thing the LHC did was confirm what we already pretty much knew.”

Woah I must have missed that part. It’s good to know that we already “pretty much know” everything without even looking for it. Maybe your excellency will just spell out what else we already know and don’t actually need to check?

Supersymmetry will not be discovered at the LHC.

Proof: String theory predicts supersymmetry (Witten 1984-2002). String theory predictions are always wrong. Hence supersymmetry does not exist, and will in particular not be found at the LHC. QED.

Corollary
Lubos Motl will lose his experimental-susy-by-2006 bet.

9. Tmark48 says:

Oh boy oh boy, from hierarchy to anthropic justifications.
SUSY is going from bad to worse. Unbelievable, simply unbelievable.

10. Eric says:

Actually, it’s very possible that supersymmetry solves the hierarchy problem with an acceptable amount of fine-tuning even if the gluino, sleptons, and squarks all have multi-TeV masses, and consquently cannot be observed at the LHC. In the context of minimal supergravity, there is a region of parameter space on the hyperbolic branch called the focus point. Spectra which lie on the focus point have low fine-tuning which is fairly insensitive to the scalar masses. For these spectra, it is easy to have the correct Higgs mass and a dark matter relic density which satisfies the WMAP limits. Since the scalar masses for these spectra are heavy it may not be possible to observe them at the LHC. However, the direct dark matter detection cross sections are within reach, so this is where supersymmetry may be found even if there is no chance of finding it at the LHC. A linear collider should be able to study the neutralinos and charginos for these spectra. I would suggest reading the review article of Jonathan Feng which is out on hep-ph today rather than misrepresenting the situation.

11. Peter Woit says:

Eric,

I did link to the Feng article and encourage people to read it who want to see the state of attempts to find still viable “natural” SUSY models. Arkani-Hamed makes it clear that he now sees these things as too complicated and contrived to be plausible, which is why he’s promoting the idea that split SUSY is the best hope. You should argue the with him the question of whether “focus-point” models are plausible, he’s not even mentioning them as worth discussing…

12. Noah Smith says:

So my question is…What’s up with Arkani-Hamed? Does he really believe the stuff he’s selling here, or is he just trying to stay in business for another decade?

13. Peter Woit says:

Noah Smith,

The interesting thing about Arkani-Hamed is that for quite a few years now, most of his research work has been in a completely different direction than BSM physics like SUSY. Instead he’s studying new ideas for a very different formalism for computing scattering amplitudes (the”positive Grassmanian”) and hopefully reformulating QFT in a dramatic way. His talks about BSM SUSY tend to focus on the issue of “What are the only remaining conceivable forms of SUSY that are viable?”, not on whether BSM SUSY is a good idea or not.

Why he (and a lot of other prominent theorists, at the IAS and elsewhere) have decided to keep promoting this as it becomes an ever more obvious failure is a good question, with the only answer I see that they feel that they and some of their colleagues have a lot invested in it. My impression is that most theorists have long ago given up on BSM SUSY as hopeless (see for instance the HEP phenomenologist bloggers like Jester and Matt Strassler). Why it continues to get so much positive attention is somewhat of a mystery. Arkani-Hamed would do the field a huge service if the next time he were asked to discuss SUSY and BSM physics he were to give a talk explaining why it’s no longer a plausible idea, and instead start promoting fundamental mathematical physics work of the sort he’s now himself doing.

14. King Ray says:

If you read Thomas Kuhn’s The Structure of Scientific Revolutions, you will recognize that we are in a stale period between paradigms. The SUSY/String Theory paradigm has not panned out after nearly 40 years of effort.
I believe that if you have a theory, you should either be able to test it experimentally, e.g., the bending of light predicted by General Relativity, or have it be able to explain a previously unexplained fact or phenomenon, e.g., the precession of the perihelion of Mercury. Otherwise you are not using the scientific method (where you test your theories), and you are going to be led astray by false aestheticisms. I heard that Feynman suggested that if superstring theory were the theory of everything, why couldn’t string theorists predict the mass of the electron?

15. Eric says:

Peter,
Arkani-Hamed hardly represents the majority view of phenomenologist who work on supersymmetric models. His is actually a fairly extreme position which you are using as a straw-man. The bottom line from my own analysis is that the superpartners can easily have masses greater than 5 TeV and the hierarchy problem can still be solved with only minor fine-tuning. If you were more of a scientist and less of a propagandist, you would know this. At any rate, pay attention to the next update from the dark matter direct detection experiments.

16. Peter Woit says:

OK Eric, interesting to hear that the majority of phenomenologists see Arkani-Hamed as an extremist (and a propagandist too I guess since you’re characterizing me that way when I’m just quoting him..). Also interesting to hear that SUSY proponents are now looking for vindication from dark matter direct detection, not the LHC.

King Ray,

I agree that what we’re seeing is the collapse of a paradigm. The problem is that the new paradigm being heavily sold is multiverse mania. Not a pretty situation. Interestingly, string theory has kind of dropped off the map as irrelevant, since it says zero about anything testable, at the LHC or elsewhere (and that’s the problem, that it predicts nothing at all, not that it doesn’t predict the electron mass).

17. Shantanu says:

Eric,
To turn it around, if dark matter experiments see nothing, would you be willing to change your opinion and agree that SUSY is dead?
Shantanu

18. Bob Jones says:

“He also is the only phenomenologist with a $3 million Fundamental Physics prize, awarded for his work on models that have had great influence, although zero success experimentally.” The prize was also awarded for his very interesting work on scattering amplitudes. “string theory has kind of dropped off the map as irrelevant” This statement is just delusional. If you look at the new hep-th submissions on arXiv, you will see that about half the articles are string theory articles. As long as string theorists are coming up with interesting results, string theory is not going to go away. 19. Bob says: Breaking news: phenomenologist gives talk about particle physics at particle conference! Woit misunderstands phenomenologist and gives a rant about the end of physics. 20. King Ray says: Bob, “hep-th submissions on arXiv”? How about “confirmed predictions at the LHC”? 21. Anonymous says: @King Ray The idea is that SUSY does (or at least, did) explain a previously unexplained phenomenon, namely the unnaturally low electroweak scale, in a very plausible way. Nowadays, criticisms of SUSY are that its explanation has become inconsistent with data, or at least that the continuing interest in SUSY is not reflecting the present absence of direct detection when in the most plausible models we should have seen something already. 22. Mitchell Porter says: The conventional reasons for believing in supersymmetry, known to me, are hierarchy problem, gauge coupling unification, dark matter, and (for theorists) string theory. But you don’t need the full supersymmetric spectrum to obtain dark matter or gauge coupling unification. So if anthropic finetuning were to become the new paradigm for explaining the Higgs mass, presumably that would weaken supersymmetry’s popularity in the long term. It could end up being regarded as a Planck-scale phenomenon only. 23. Bob says: This is wrong. The only indication we ever had that susy is right is its prediction of gauge coupling unification. This fact has not been undone by the current data, no matter how much ppl might kick and scream about it. Let’s also remember that every other proposal for new physics at the weak scale is clearly dead. Susy is the only remaining idea that hasn’t been totally killed yet, though low energy susy is a bit injured, while high energy susy is still fine. 24. Bob Jones says: King Ray, Most of the string theory articles submitted to arXiv are about applications of the AdS/CFT correspondence, and while they do not make BSM predictions, some of them do make contact with experimentally testable phenomena in nuclear and condensed matter physics. So far, the only prediction of new physics which has been confirmed at the LHC was the prediction of the Higgs boson. Besides Higgs et al, nobody has made a successful prediction, so I don’t think it makes sense to criticize string theory specifically for not making LHC predictions. 25. Peter Woit says: Bob Jones, It’s not “his” work on scattering amplitudes, he’s only one of quite a few people who have worked on this. If there was going to be a$3 million award for advances in scattering amplitudes, it would be going to other people.

The reference to string theory “dropping off the map” was about BSM physics and the LHC. I think the consensus is now quite clear that string theory is irrelevant to the LHC, as well as any other conceivable experiment. You virtually never anymore see what used to be the usual nonsense in the press about “predictions of string theory”, as string theorists have mostly given up putting out such press releases.

“Bob”,
Perhaps you could consider explaining just what it is that I don’t understand here.

“The only indication we ever had that susy is right is its prediction of gauge coupling unification.”

So, that whole hierarchy thing, no one ever really meant those arguments for susy? And the WIMP miracle, that’s not serious either? The only argument for SUSY is that if you believe in a desert up to the LHC, and you believe in GUTs (for which there is zero evidence) then you get a number coming out right to 10-20%? That’s all that SUSY has ever had going for it? Wow…

26. onymous says:

I thought the idea that the focus point scenario can lead to low fine-tuning even with multi-TeV scalars had been unceremoniously buried many years ago. It seems to require a really odd set of assumptions to be believed (for instance, you’re allowed to ask how sensitive the theory is to varying a universal scalar mass, but not to varying the top Yukawa or varying scalar masses in a nonuniversal way). I’m not really sure why it’s being resurrected. If you really think you understand the set of top-down theories that could be realized in nature well enough to make this argument, more power to you, but the argument is often repeated without all the necessary caveats.

It’s my belief that all models of natural SUSY suck. (I worked on one myself, and it sucks too.) Direct SUSY limits are mildly troubling, but the elephant in the room is the Higgs mass, which just obliterated almost all sensible models of natural SUSY. The contortions people go through to save a bit of fine-tuning just seem absurd to me. Complicating your theory to save fine-tuning isn’t really winning. I think it is important and interesting that the LHC rule out these scenarios, but none of them are remotely plausible. Maybe if you posit compositeness right around the corner or something extreme like that you can find some room to live, but it seems unlikely that Nature is that kind of Rube Goldberg machine.

It’s a really, really unpopular opinion in the hep-ph community, but I think what Nima says is exactly right: the only plausible-looking incarnation of SUSY we have left is the “semi-split” scenario with scalars at 100 or 1000 TeV. It’s still a hell of a lot more natural than the Standard Model alone, and it gives gauge coupling unification, so I wouldn’t bet against it. This is not your grand-advisor’s SUSY scenario, though, and the community should be more honest about that.

The Opera neutrino anomaly basically wiped out any illusions I had left that the hep-ph community as a whole was serious and intellectually honest.

27. Bob Jones says:

“It’s not ‘his’ work on scattering amplitudes”

No, it’s certainly not his exclusively, but he has played a leading role in recent work on scattering amplitudes, and this is acknowledged in the prize citation.

“You virtually never anymore see what used to be the usual nonsense in the press about ‘predictions of string theory'”

Yeah, but press releases are not an accurate indicator of what’s happening in a field. The fact that jounalists are not talking about “predictions of string theory” does not mean that string theory dropped off the map. String theory is still a very important direction in current research, and regarding LHC predictions, the situation for string theory has not changed recently.

28. chris says:

i would pity the poor susy phenomenologists for the miserable state they are in: having to defend an obviously obsolete theory. i would pity them had they not all the best-paying and most prestigeous faculty positions.

for the greater good of physics one can only hope that their failure will at one point be publicly recognized as complete and they will be ridiculed out of their preposterous ideas. i fear that nothing else will stop this madness.

29. Anonyrat says:

So Arkani-Hamed won $3 million for work done in the last two years? That is the conclusion it seems one must draw if one looks at the top-cites for 2010: http://www.slac.stanford.edu/spires/topcites/2010/annual.shtml (I can’t find a more recent topcites.) 30. prepo says: Sir Joseph Larmor is remembered today for Larmor precession and his formula for the radiation by a nonrelativistic accelerating charge, yet in his day his most famous work was his Adams Prize essay “Aether and Matter”. You can still buy it of you wish http://www.amazon.com/Aether-matter-Joseph-Larmor/dp/B00385WM14 Larmor was appointed to the Lucasian chair of mathematics. He retired in 1932 and was succeeded by Dirac. Nobody laughed Larmor out of his preposterous ideas. 31. Anonyrat says: Ah, here is the INSPIRES 2011 annual list: http://inspirehep.net/info/hep/stats/topcites/2011/annual.html and the 2011 all-time list: http://inspirehep.net/info/hep/stats/topcites/2011/alltime.html Still no indication. 32. Anonyrat says: Larmor’s 1900 essay “Aether and Matter” is available online here: http://archive.org/details/aetherandmatter01larmgoog Wiki says: “.Larmor opposed Albert Einstein’s theory of relativity (though he supported it for a short time). Larmor rejected both the curvature of space and the special theory of relativity, to the extent that he claimed that an absolute time was essential to astronomy (Larmor 1924, 1927).” So I guess prepo’s point is borne out. 33. Peter Woit says: Anonyrat, Arkani- Hamed’s http://arxiv.org/abs/hep-ph/9803315 (with Dimopoulos) has about 4500 citations, making it one of the most influential and heavily cited HEP papers of all time. On the all-time top-cites list you give, it is number 7, led only by Weinberg’s 67 paper, Kobayashi-Maskawa since everyone doing flavor physics quotes that, the 3 early papers on AdS/CFT that everyone quotes, and Randall-Sundrum. It’s the first thing mentioned in his Milner prize citation. The other remarkable thing about it is that no one ever seriously believed this kind of model was plausible, and LHC results quickly ruled it out at accessible energies. I suppose you could claim that maybe it will show up at higher energies, but I don’t know of anyone who would bet on that, even given very advantageous odds. All IAS HEP professors got Milner prizes, and Arkani-Hamed got his IAS professorship around the time he started working on amplitudes. Put differently, if he had never worked on amplitudes, he’d still be an IAS professor, and surely also a Milner prize winner… 34. Anonyrat says: Thanks for clearing that up. I thought Bob Jones has written that Arkani-Hamed’s$3 million prize was for his work on scattering amplitudes, and since A-H’s most cited paper was on extra dimensions, and none of his scattering amplitude work upto 2011 was cited any where close to that, I was quite puzzled.

Regarding Wilczek, recall what he wrote in his Future Summary back in 2001 (p 20):

“5.5. Produce the New Particles!
Of course, the ultimate test for low-energy supersymmetry will be to produce some of the predicted new R-odd particles. Even in the focus point scenario, there must be several accessible to the LHC

36. new particles says:

Let’s not get carried away about the failure of new particles to appear at LHC energies. With all of the euphoria of the success of QED renormalization in the post-WW2 years, nobody predicted the appearance of the V-particles (later called strange particles). In later years, after the discovery of charm, nobody said there would be a third generation of quarks, and there would be a new family of narrow resonances at approx 10 GeV. By 1975 the Standard Model was in place, but the Upsilon was discovered in 1977. The SM didn’t predict the (b,t) generation. Although once the b was found, the top was immediately claimed to exist, but no theorist could quantify its mass. Gordy Kane’s calculation notwithstanding, no theorist (from 1960s to 2000s) could quantify the mass of the Higgs either. There isn’t really any quantitative non-SUSY (or non-string) prediction of what the next generation of BSM particles will be, nor what their mass scale will be. (I suppose there is the axion …)

37. Philip Gibbs says:

new particles, the third generation was predicted in 1973 by Makoto Kobayashi and Toshihide Maskawa to account for observed CP violations. I think you are right that nobody predicted strangeness though, or even muons.

38. Philip Gibbs says:

New Scientist also has a quick interview with Milner this week.

39. new particles says:

Aha. The appearance of the Upsilon at approx 10 GeV was a surprise, though. Nobody knew the mass scale of the third generation quarks. This was very clearly demonstrated by the top quark. Once the b was found, nobody doubted the t would exist. But nobody had the faintest idea of its mass. A whole string of machines (PEP, PETRA, TRISTAN, LEP … others?) all failed to produce the top. Eventually the Tevatron did, but there was no a priori proof that the design energy of the Tevatron (as a collider) would be sufficient to produce the top. As for the muon, that is a classic. It took many years to demonstrate that the muon was NOT the Yukawa particle, and to find that there were in fact two particles, the pion and the muon. And as Isidor Rabi famously said, when the muon was recognized to be a lepton, “Who ordered that?” Nobody expected a heavier version of the electron to exist.

SUSY may be getting more and more constrained in parameter space, but for the most part nobody has ever had any really good idea of the mass scale and properties of the next generation of particles.

40. Mitchell Porter says:

“new particles” said

“Gordy Kane’s calculation notwithstanding, no theorist (from 1960s to 2000s) could quantify the mass of the Higgs either”

Shaposhnikov and Wetterich obtained it http://arxiv.org/abs/0912.0208 … by assuming a desert between the weak scale and the Planck scale, and by assuming that the Higgs quartic coupling goes to zero at the Planck scale.

Also, to be fair, Dharwadker and Khachatryan http://arxiv.org/abs/0912.5189 managed to predict it … in a crackpot paper which issued in the formula “Higgs mass equals half the sum of W+, W-, and Z masses”.

41. new particles says:

Good! So tell us all the mass of the nearest BSM particles, and their symmetries and interactions! There’s no need to post items about the lack of observation of SUSY!

42. Pi says:

Is there any chance that the LHC tell us at least if there’s such thing as unnatural SUSY that Arkani-Hmaed et al are talking about?

43. Peter Woit says:

Pi,

According to the authors of the paper whose final part I quoted, the answer is “only if we’re lucky”.

44. Cliff says:

“Once one abandons the hierarchy argument, the remaining arguments for SUSY are extremely weak”

Thats simply not true. Naturalness is a rough guide to finding the correct description, but it is not an inconsistency! By contrast, any of your attempts to describe the quantum field theory together with general relativity without using SUSY go ‘Glub, glub, glub’ right to the bottom of the sea. There is just no way to argue that the aesthetic criterion of naturalness (as useful as it may be in many cases) is more important that mathematical consistency.

From what I understand about F-SU(5), it is confined to a distinct window of parameter space and can be definitively ruled out at the LHC. I think its pretty awesome that a totally falsifiable model is putting forward explanations for the vacuum energy problem and other things. It looks kind of unfair to me that you’ve reduced it to a cheap punchline that supports your own eternally pessimistic viewpoint. The F-SU(5) explanation for why most SUSY searches have come up empty seems worth taking seriously: the cuts on missing transverse energy are too high, and the production of superpartners may be very soft.

Decrying the “conventional wisdom” of using supersymmetry as a fundamental principle for unification isn’t actually going to help advance the field in any way. Especially as long as SUSY remains the only mathematically viable principle to put the ‘big picture’ together. But if SUSY turns out not to be a feature of the low-energy world, that may be that. As you’ve implied, there may unfortunately be an end to what we can see. That’s not some grand crisis, that would just be life. But I remain somewhat more optimistic at this point.

45. Peter Woit says:

Cliff,

I don’t think it’s me who has reduced F-SU(5) to a “cheap punchline”, but rather those who think it is a good idea to put out a new paper every few months about their latest “predictions” and how they are seeing (or smelling…) evidence for this theory in the data, just to have this conclusively falsified days or weeks later by new data (leading to another paper…). Maybe in 2016 or so these authors will stop smelling things and write a paper acknowledging that the idea is wrong. I’ll believe that when I see it.

As for a “grand crisis” caused by failure to find SUSY, my point of view is rather that not finding SUSY at the LHC might finally start causing people to give up on a bad idea (SUSY extensions of the SM like the MSSM) and working on something more promising. So, not a “grand crisis”, but an opportunity, one that some prominent theorists are digging in their heels trying to stop from arriving.

46. Garrett says:

The gauge coupling unification result from SUSY is impressive, but this can happen more economically by just adding a handfull of Higgs multiplets.

47. King Ray says:

Mitchell,

Thanks for the link to the Shaposhnikov and Wetterich paper. In their closing statements they say

“Detecting the Higgs scalar with mass around 126 GeV at the LHC could give a strong hint for the absence of new physics inﬂuencing the running of the SM couplings between the Fermi and Planck/uniﬁcation scales.”

This is very interesting, and may not bode well for BSM physics. It is intriguing that a prediction of the Higgs mass might arise from SM and gravitational considerations. It will be curious to see how well their prediction matches the final Higgs mass.

48. Bob says:

” . . . my point of view is rather that not finding SUSY at the LHC might finally start causing people to give up on a bad idea (SUSY extensions of the SM like the MSSM) and working on something more promising.”

What looks more promising these days?

49. Toni says:

The susy experts all speak and dream of coupling constant unification. But there is no good reason why these should unify. This is a wish, a hope, a dream. Grand unification, even as an approximation has no basis. As long as we suspect that the dream is true, we will not get susy in the waste basket – where it belongs.