# WIMPs on Death Row

One of the main arguments given for the idea of supersymmetric extensions of the standard model has been what SUSY enthusiasts call the “WIMP Miracle” (WIMP=Weakly Interacting Massive Particle). This is the claim that such SUSY models include a stable very massive weakly interacting particle that could provide an explanation for dark matter.

According to the “WIMP Miracle”, evidence for such a particle is supposed to show up as they get produced at the LHC, and at underground detectors designed to look for ones traveling through the earth. Like all other predicted SUSY particles, no evidence for such a thing has appeared at the LHC. A sequence of more and more sensitive underground experiments has also come up empty.

One of the latest of these, LUX, announced results today, see here, press release here. These are the results from the final 20 month run of the LUX detector and they are conclusively negative: no candidate events were seen, putting four times smaller bounds on the cross-section for any such particle. New Scientist has it right I think, with a story headlined Dark matter no-show puts favoured particles on death row. Ethan Siegel has a very good article, Dark Matter May Be Completely Invisible, Concludes World’s Most Sensitive Search, which includes:

The null detection is incredible, with a fantastic slew of implications:

1. Dark matter is most likely not made up, 100%, of the most commonly thought-of WIMP candidates.
2. It is highly unlikely that whatever dark matter is, in light of the LUX results, will be produced at the LHC.
3. And it is quite likely that dark matter lies outside of the standard mass range, either much lower (as with axions or sterile neutrinos) or much higher (as with WIMPzillas).

Enthusiasts are not likely to give up so easily though, with Sean Carroll tweeting that the news is only “we’re not seeing it yet, stay tuned.” Not sure what one is supposed to stay tuned to, this is pretty much a final result from LUX. There will be a next generation experiment, LZ, but that’s for after 2020. There are other competing experiments now operating, including Xenon1T, now being commissioned, which will be somewhat more sensitive. There seems to be no serious reason though to expect WIMPs to appear at somewhat lower cross-sections if they haven’t appeared yet.

With SUSY and the “WIMP miracle” now dead ideas, perhaps that will lead to focus on more promising ones. There is still a great deal that we don’t understand about neutrinos. A few days ago I saw this intriguing news about the PTOLEMY project, which I hadn’t heard about before.

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### 52 Responses to WIMPs on Death Row

1. M says:

“WIMPs on Death Row” is hype, altought negative. What gets more in trouble is WIMP interacting with nucleons at tree-level and in s-wave. WIMP that interacts through electroweak loops is ok. WIMP with a p-wave non-relativistic suppression is ok.

2. Peter Woit says:

M,
Thanks. But is there any motivation for such models, at a level visible with another order of magnitude sensitivity, or would such things always be likely invisible to this kind of experiment?

3. I will ask this because I’m too lazy to read extensively to figure out the answer: Is the LUX result directly incompatible w/ the DAMA claims?

4. Peter Woit says:

Douglas Natelson,

Even the earlier LUX results were incompatible with DAMA, see for instance
http://arxiv.org/abs/1406.5200

5. Jeffrey M says:

OK, I’m confused. DAMA observed changes in dark matter flux based on the earth’s orbit, right? But LUX says no such thing could have happened? Or only that it couldn’t be WIMP’s?

6. Peter Woit says:

Jeffrey M,
If you believe DAMA’s interpretation of the periodic effect in their data as due to a WIMP, that implies a WIMP cross-section (probability of interacting with a nucleon) so large that LUX should be seeing a sizable signal. In this sense, LUX rules out the idea that DAMA is seeing WIMPs.

7. Marc says:

Peter–Often the DM experimental results show, in the plot of cross-section vs mass, a large gray area in the lower right which corresponds to the predictions of typical SUSY models. While this experiment takes out a big chunk of it, it only looks like about 1/2 of the gray area. So doesn’t Death Row seem a tad bit premature?

8. Peter Woit says:

Marc,
The problem is that the meaning of “typical SUSY model” and the associated grey blobs are ill-defined and move as the experiments get more sensitive. For example, a few minutes research turned up some 2001 SUSY “predictions”, see
http://arxiv.org/abs/hep-ph/0106148
where the conclusion is
“When CDMS is moved to the Soudan mine, its sensitivity will drop to between 10^-8 and 10^-7 pb and GENIUS claims to be able to reach 10^-9. At those levels, direct detection experiments will either discover supersymmetric dark matter or impose serious constraints on supersymmetric models.

The LUX result is below 10^{-9} pb over a very large range, down to 2.2 x10^-10 at 50 GeV. So, it is very much “imposing serious constraints” on SUSY, but of course there will always be SUSY models with smaller cross sections. I don’t think there’s a sensible way to put a measure on such things.

9. Jeffrey M says:

Thanks Peter. So DAMA was explicitly claiming WIMPS, which LUX rules out. Got it. Should we expect a surge of papers explaining DAMA in some different way?

10. Peter Woit says:

Jeffrey M,
The interpretation of the DAMA signal as being due to dark matter was already ruled out by earlier experiments, including early data from LUX. So, there’s nothing new about that here. I haven’t followed the latest in attempts to explain the DAMA signal, but, since it is just an annual modulation, one can imagine all sorts of non-fundamental sources due to a subtle seasonal variation in the environment of the experiment.

11. M says:

One example of an alive&healthy WIMP is (in SUSY langauge) an umixed Wino. Or, more generically, a weak triplet with zero hypercharge. It interacts only with heavy electroweak vectors, giving a loop-level direct detection cross section below present bounds and a little above the neutrino background.

12. Tom Andersen says:

Peter,

Theorists should not diminish experimental results they don’t understand, based solely on the fact that they can’t predict them.

Don’t you think that the DAMA team has used various techniques to improve any seasonal environment variations? Despite all efforts at this the signal amplitude remains the same. Is it a WIMP dark matter signal? No. Is it real? Looks likely.

There are now a few direct reproductions of the DAMA experiment. Let the experimenters decide this one.

13. Peter Woit says:

Tom Andersen,

You’re reading things into what I wrote that aren’t there. Of course I’m aware that the DAMA people (and others) have done their best to identify environmental sources of the signal. They are seeing something, but my understanding is that the results from other experiments show that it’s not the hoped for WIMP signal, and that currently no one knows what it is. Given this, an environmental source remains a possibility, as well as something much more interesting. I have no idea what relative probabilities to assign to those two alternatives, was not implying anything about that issue at all.

14. Chris Austin says:

M,

“One example of an alive&healthy WIMP is (in SUSY langauge) an umixed Wino. Or, more generically, a weak triplet with zero hypercharge.”

Do you mean just the electrically neutral component of the triplet?

15. Peter Woit says:

Chris Austin,
If it’s not electrically neutral, it’s not a WIMP…

16. Bernhard says:

If not DM directly, there is still hope to find evidence on the existence of other stuff from the dark sector at the LHC (like dark photons).

17. piscator says:

Tom: talk off-line to experimenters involved in other WIMP DM searches and ask them their opinion of DAMA’s claims. It is not just theorists who are sceptical about DAMA’s results.

Peter,
My reading of Chris Austin’s comment is that he was pointing out exactly what you said. Perhaps he could phrased it better: “Do[n’t] you mean just the electrically neutral component of the triplet?”

19. M says:

Chris, yes. Its direct detection cross section is ≈ 0.3 10^-46 cm^2

Interesting news, but in what sense are SUSY or WIMP DM dead ideas? There exists parameter space that wasn’t excluded by any experiments. They are alive.

I suppose you mean that they’re less plausible in light of LUX latest results? Can you elaborate on your reasoning? In the past you dismissed inductive (Bayesian) reasoning in science, but now you suggest that the plausibility of particular models has changed in light of data.

Have you changed your mind? If so, very good. If not, OK, but don’t argue that the status of SUSY DM or WIMP was affected – it has the same status as before, unfalsified.

21. Yatima says:

it has the same status as before, unfalsified

The correct adjective here is (still) “unjustified”.

That being said here is report on the possibility that Dark Matter is mainly formed by a large population of primordial black holes (thus, a galactic halo of black hole “gas”). I am not sure whether this fits the (AFAIK) sparse observations of lensing events.

22. Peter Woit says:

The last thing in the world I want to get into is a debate over Bayesian reasoning, but I’ll point out that my criticisms and mocking of it had to do with its misuse (things like Polchinski’s calculation of probability of a multiverse), not with its use to characterize the significance of experimental results.

Obviously SUSY is unfalsifiable due to its huge parameter space,, always has been, always will be, and John Ellis I think has stated that he’ll never abandon it. Equally obviously the “WIMP miracle” is not working out, and in that sense the idea is on its way to the graveyard of failed ideas.

Fair enough, that makes sense to me. These DM results are pretty cool, and I enjoy reading your blog. Enjoy the weekend.

24. DP says:

Hi Peter, you might be interested in the new announcement from the PandaX Dark Matter Experiment.

25. Andreas says:

Hey Peter! Thanks for this news, i haven’t seen it yet. Concerning dark matter, what did you think about Adam Riess’ recent investigation: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.201301 ?

26. Peter Woit says:

Andreas,
Sorry, but you really need an astronomer to evaluate that idea, not me.

DP,
Thanks! I took a quick look at
http://pandax.physics.sjtu.edu.cn/files/pandax_ii_idm.pdf
and their new result seems to be quite similar to the LUX result (best limit 2.7 x 10^{-10}pb at 40 GeV, vs 2.2 at 50 GeV). Not sure why LUX is getting all the atttention.
Perhaps combining the two results one might get even more stringent exclusion limits.

27. MikeS says:

Until we have some better explanation of Dark Matter, WIMPs of some form must remain a contender. We either have to establish a theory that Dark Matter does not exist, or we have to find where it is hiding. And in the case of the latter, there are precious few theories.

I suspect it is simply the hitching of WIMPs to the SUSY bandwagon, and the rather circular logic whereby one seems to promote the probability of the other that people object to.

28. Doug McDonald says:

There are no pointers to papers above, and a quick search didn’t find what I want.
Question from an experimentalist: I read the Panda Powerpoint. It quotes a
maximum cross section versus energy.

BUT … such an experiment measures the PRODUCT of a cross section times a flux.

There is no measurement of a flux! They must be assuming something … is it something astronomical?

29. Doug McDonald:

The experiments measure events per time in each energy bin. A simple discussion of WIMP direct detection can be found on pages 116-117 of my lecture notes.

http://www.courses.physics.helsinki.fi/teor/cos1/cosmo2015_07.pdf

30. Tim says:

Doug,

The “WIMP Miracle” mentioned in the post is that if you assume a certain cross section and mass that are compatible with a particle that interacts via interactions at the “weak” scale, then the standard model + big bang nucleosynthesis produces it in the right amounts and with the right energies to explain both the amount and spatial distribution of observed dark matter. You can calculate the expected flux from that.

Once the expected flux * expected cross section is not observed, it’s still possible that dark matter exists with other smaller values, but the connection to a particle (potentially supersymmetric) interacting at the weak scale is lost.

So there you go. The assumptions come from theoretical predictions of formerly popular models that seemed to explain our dark matter observations quite nicely. Unfortunately this + LHC bounds now suggest that the right answer now seems to be something other than a weak scale lightest supersymmetric particle.

31. GoletaBeach says:

Peter, wow. Just within the realm of SUSY models, plenty, plenty of models predict WIMPs with cross sections lower than LUX, XENON1T, or even LZ sensitivity.

Some questions only have empirical answers, and thank goodness that particle experimenters have traditionally only lightly paid attention to theorists’ hype.

There was tremendous disrespect for Ray Davis and his neutrino experiment from theorists… I remember it well. There was disrespect for all the many, many searches for neutrino mass/mixing, because, there was no good theoretical prediction for delta-m-squareds. Or the mixing angles. Thank goodness experimentalists soldier on.

I even remember when the weak interaction was agreed by all theorists, Fermi too (who died in 1954) to be S+T. It turned out to be V-A with no theoretical prediction of that, although Lee and Yang eventually followed up on Ernest Lawrence’s admonition, Who the he** cares about parity violation, this is experiment!’ in response to the tau-theta puzzle.

Declaring the WIMP miracle’ dead is so obviously premature that you have just joined the scammers and hype-meisters that you often criticize. I guess you are jealous of them, that their scamming gets publicity and your doesn’t.

32. Chris Kennedy says:

So how could neutrino mass be a possible explanation for dark matter? Seems to me that since galaxies come in a variety of baryonic mass distributions from center to edge, the neutrino mass distribution would always (and conveniently) have to be such that it is arranged to produce near-flat rotation curves for all varieties of galaxy. In my opinion, the odds of that are off the chart.

33. Peter Woit says:

Goleta Beach,
No disrespect to these experiments intended. They’re doing an impressive job of repeatedly pushing down limits by large factors. It’s great that people are doing them, they’re looking somewhere no one has ever looked, and if they find something it will revolutionize physics. Yes, such experiments should be done, no matter what theorists say about the likelihood of them seeing something.

That said, I still think it’s important to admit that these huge improvements on the limits carry implications for certain theoretical ideas. I just googled for more info about the GENIUS proposal that Ellis et al. mention. The 1998 proposal, see
http://arxiv.org/abs/nucl-ex/9801004
states in the abstract:
“The entire MSSM parameter space for prediction of neutralinos as dark matter particles could be covered already in a first step of the full experiment “. If I’m reading figure 3 properly, the entire region of points plotted as such “predictions” is now ruled out by LUX. For twenty years I’ve been seeing plots of this kind and claims of various kinds that SUSY dark matter models imply a WIMP in this region. Now that such things are ruled out, acknowledgement of previous “predictions” that have been falsified would be a good idea, before moving on to new models and new “predictions”.

The “miracle” in the SUSY “WIMP miracle” was always hype, but one reason it got attention was that it appeared to make a specific claim that something would be seen at the LHC and in experiments with sensitivity like that of LUX. Sure, of course WIMP dark matter isn’t dead, maybe it’s there at lower cross-sections. But it seems to me the “miracle” is dead, and it should be given a proper public burial.

Chris Kennedy,

My understanding is that right-handed (sterile) neutrino models can readily provide dark matter.

34. GoletaBeach says:

The miracle’ was that weak interaction order-of-magnitude cross sections + thermal equilibrium in the early universe easily accommodate the observed dark matter density… noticed by Ben Lee and Steven Weinberg in the 1970’s. Has not a thing to do with SUSY, and lasting interest in the WIMP being a right-handed neutrino (or left-handed antineutrinos) is traceable to that miracle’. Maybe couplings to the right-handed sector were appreciable in the weak interaction in the early universe.

Your opinion, if based on anything related to SUSY, won’t influence any serious scientists’ opinion about the WIMP miracle. Maybe you’ll help grow some anti-WIMP feelings among popular science hobbyists, though.

As for the SUSY connection, there is and will always be hope that SUSY is related to the weak interaction, and so that is the connection that seems to mainly be in your crosshairs.

Referencing H.V. Klapdor-Kleingrothaus doesn’t raise the level of the discussion. He discovered neutrinoless double beta decay, although nobody else agrees with his discovery.

Perhaps take a look at https://arxiv.org/abs/1604.07336 . Figures 2 and 5, and, the paper seems to indicate that scalar and gaugino masses were only scanned up to 2 TeV. It may be that scanning to 100 TeV or more yields a lot more low-cross section neutralino likelihood. Those plots are for the fewest free parameter CMSSM.

The 2 TeV limits? Motivated by only scanning where the LHC can see stuff. It is entirely possible that SUSY is there, unobservable a the LHC, but detectable by direct detection experiments. Or, detectable only by indirect detection (Veritas, CTA, Pingu, etc).

More parameters than the CMSSM? No problem, figure 3 of https://arxiv.org/abs/1503.00599, in the 9-parameter MSSM.

Of course we all want to see revisions after Run-2 LHC results are presented.

35. Peter Woit says:

GoletaBeach,
Maybe this is my lack of education, but all the public discussions of the term “WIMP miracle” that I remember seeing claim as a big part of the “miracle” the LSP in SUSY, I had assumed that when people referred to the “miracle”, they had in mind the “miracle” of SUSY predicting a weak-scale stable particle. For an example of what I have in mind, see
http://www.symmetrymagazine.org/article/july-2015/miraculous-wimps

“When researchers use the properties of the lightest supersymmetric particle to calculate how many of them would still be around today, they end up with a number that matches closely the amount of dark matter experimentally observed—a link referred to as the “WIMP miracle.””

I’m curious if you know who first used this term, did Ben Lee or Steve Weinberg call it that way back when? I always assumed it was part of the SUSY/String theory hype (who else calls a very rough coincidence good only within several orders of magnitude a “miracle”?)

I don’t doubt that there’s plenty of room in SUSY parameter space and that you can find recent plots with susy models “predicting” some region to the lower right of the latest exclusion. What I’m objecting to is ignoring all the similar plots I’ve seen over the years, put forward by people promoting SUSY. If you Google “wimp miracle”, the first two things that turn up are
https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles
which has a 2004 plot of the area SUSY is supposed to show up at that is now disallowed, and then this from 2009
http://www.ps.uci.edu/~jlf/research/presentations/0912upenn.pdf
which (page 9) has a plot claiming a “universal prediction” of a 10^{-44} cm^2 cross-section (also now completely disallowed).

As for what this does to the public perception of science, I don’t think 20 years of heavily hyped “predictions” based on a “miracle”, followed by “oh, just forget those, we’ve got new ones” when they’re conclusively falsified is a healthy situation.

Theorists and experimentalists who want to communicate with the public about the implications of these results (together with those from the LHC) for theory it seems to me should tell a straightforward and accurate story: experimental results have not shown what was expected, so these ideas are pretty much dead. This is what scientific progress looks like. Yes, there are always more models, and very good reasons to keep looking, but the general ideas behind SUSY extensions of the SM are no longer a particularly plausible motivation for anything. Abandoning these and moving on to other more promising ideas (let’s hear more about right-handed neutrinos, less about neutralinos) would be a good idea.

36. GoletaBeach says:

I’m not an etymologist… appears that the earliest (1985) reference to WIMP, has no mention I see of SUSY…
http://ac.els-cdn.com/0550321385905371/1-s2.0-0550321385905371-main.pdf?_tid=4ae66064-538d-11e6-a255-00000aab0f26&acdnat=1469577879_0f1061aceb68f51962bd19520d599e70

And earliest WIMP Miracle (2007, possibly from Feng alone) is on the first 4 slides of:
http://theory.fnal.gov/jetp/talks/feng.pdf

Note that the SUSY stuff in that 2007 talk is *after *the WIMP miracle.

The logic is (thermal equilibrium) + (weak interaction) = WIMP miracle.

SUSY only chases that ambulance. If some people get it wrong, that is their mistake.

As experimental data accumulates, simple scientific principles require any well-defined phenomenology to adapt to respect the new experimental data. And so it goes with SUSY phenomenology… the very simplest SUSY phenomenology, the CMSSM, still has plenty of room for an LSP that is the WIMP, even after all known data (through LHC run 1) is accommodated. But even if someday experimenters doing good science eliminate all viable CMSSM parameter space, all they will do is prove the CMSSM LSP is not the WIMP. The WIMP miracle will remain untouched.

Of course the MSSM has less simple parameterizations than the CMSSM. As I pointed out, in those less simple parameterizations, there is even more room for an LSP that is the WIMP.

The above is just: SCIENCE!!! SUSY has loads of parameters. Ruling it out is a lot of work. Just as proving global warming was man-driven was a lot of work. Welcome to real science.

The LUX results are entirely consistent with what is expected under both SUSY and the separate and distinct WIMP miracle. There is no “conclusively falsified” anything here.

In the talk you link, and the plot you refer to, Baltz and Gondolo’s predictions went off the bottom of the plot. Feng took a specific category of models and pointed at 10^(-44) cm^2. Obviously other models weren’t covered by his pointing. And Feng ain’t a consensus Snowmass or NAS report. If you don’t like Feng’s hype, take it up with him. Tainting a whole field with one (possible) hypester is not good. And Wikipedia? Seriously?

Real science is a complicated, messy thing. It clearly frustrates you that simple stories you have decided are true are not. What frustrates me is that good experimental science effort is likely to be impeded by your cartoonish simplifications.

37. Peter Woit says:

GoletaBeach,
Interesting that the terminology is that recent, I had no idea. I would have thought it went back to SUSY enthusiasts of long ago. Whoever it’s due to though, I think it’s a bad idea, misleading hype. Would be better to find another one.

While doing a bit of looking at old papers/slides to see where the “miracle” came from, just about every one of them has a plot of susy predictions that are now conclusively falsified (often the range of the LUX results isn’t even plotted). This isn’t just Feng.

Look, experimentalists should do what they can do: design and build the best experiments to look where no one has looked before. I don’t see why they should get into questions about complicated BSM models that have no good motivation. Theorists should be the ones evaluating such models, and they are the ones I’m claiming need to look at the long, sorry tale of SUSY extensions of the SM, draw the conclusion it’s no longer a promising idea, and not continue down the rabbit hole of promoting ever less motivated corners of SUSY parameter space.

I’m well aware this is a complicated story (actually I wrote a whole chapter in my book long ago about SUSY, precisely because it is a complicated subject). I should have realized that I didn’t write about the “miracle”, because it wasn’t called such back when I was writing (2002-3). But, despite all the complexities, there are now a lot of very good reasons to call SUSY extensions of the SM a failed idea. I wrote about a bunch back in 2002-3, the LHC has given us a bunch more, and so have experiments like LUX. No, you can’t ever completely rule out something like the SUSY framework, but you can get to the point where its original motivations haven’t worked out and it has become highly implausible. We’re there now.

38. GoletaBeach says:

The original (thermal equilibrium) + (weak interaction) = currently observed relic density is very compelling, and independent of SUSY. That is the hype’ that most serious speakers point to. Feng named it the WIMP miracle. Weinberg and Lee pointed it out in the 1970’s, and in the 1980’s that connection lead to the first WIMP searches… when the big idea was to test whether the WIMP had V couplings like heavy Dirac neutrinos… in the 1980’s that was ruled out. No-one called it the WIMP miracle but everybody knew what was going on. SUSY didn’t matter at that time, although the attraction of the LSP (then called the photino) being the WIMP started to be discussed.

Only recently has WIMP sensitivity of experiments achieved the expectation for A couplings like Majorana neutrinos. People in the thick of things know this, you don’t, you keep projecting SUSY BS onto the field.

And guess what… long before you were around the usual experimental introduction to anything w/r to SUSY was… There is no experimental evidence that supports SUSY. But SUSY has withstood the test of time.’ It is sardonic.

That SUSY might be restored at a mass scale a bit higher than accelerator folks want is not important for a possible LSP/WIMP connection. The cancellations that SUSY provides to regulate infinities work just fine even if a 500 TeV collider would see absolutely no evidence of SUSY, so the original motivation for SUSY is intact.

39. Peter Woit says:

GoletaBeach,
Thanks, I’d love to hear more about the possible role of Majorana neutrinos here. I think those working in this area would do well to discuss such topics when describing publicly motivation for these experiments, rather than trying to emphasize SUSY motivations that have not worked out.

40. GoletaBeach says:

Most experienced experimentalists are fairly ecumenical about SUSY. It is another good reason to look for stuff, but not the only reason. Phenomenological SUSY provides serious numerical modeling and serious model building. Lots of phenomenologists work hard on scanning its super-big range of parameters. That is all good science…

Sure, people oversell SUSY. One of those people is you, who want to portray the testing of SUSY as a straight up and down test, like the Michaelson Morley experiment. It is not.

It is perfectly possible that a peculiar corner of SUSY parameter space out of reach of LHC or the Great Collider or Veritas or CTA or LZ is what Nature chose. If eventually some experiment 500 years from now figures that out, I’m sure theorists 500 years from now will say that Nature’s solution is beautiful and natural.

But that is not a serious argument to cease experimentation and returning to theological debates over naturalness or the anthropic principle or the nature of transubstantiation.
Doing the best experiments we can afford remains a better use of our time. Sometimes we do the wrong experiments and sometimes indelicate hype gets used to justify the correct experiment. I wish we were all perfect but we are not.

41. GoletaBeach says:

A/Majorana… something published is Fig. 1 in:
https://arxiv.org/pdf/astro-ph/0509269v2.pdf shows where the Majorana line was.

Latest LUX among others blew through that line over much of the mass range
https://arxiv.org/pdf/1602.03489v3.pdf

42. Peter Woit says:

GoletaBeach,

You’re missing the context of what I write about SUSY here. I’m very aware of the complexities, have been following the story since the very early 80s (when I was a graduate student at Princeton, Witten was telling students they should learn about supersymmetry, Julius Wess was a visitor, giving a series of lectures that ended up as the book with John Bagger). When I was a postdoc at Stony Brook during the mid 80s, SUSY/supergravity was something hard to ignore.

From the beginning though, I found that SUSY didn’t provide any convincing explanations about the SM. Over the years it has become a hugely oversold subject, partly by making claims (e.g. “SUSY solves the hierarchy problem, so superpartners will be seen at LEP, Tevatron, LHC, etc..”) that have always failed. My impression of the way most theorists felt about SUSY a few years ago was increasing skepticism, with the LHC results to come the final and last hope. Now that those have come in, I think people need to draw the appropriate conclusions, not go on for the rest of all our lives saying “still a great idea, just have to go to higher masses”

So, sure, you’re going to see me keep arguing that new LHC results are nails in the coffin (I think we’ll see more in a week or two at ICHEP) of a bad idea that never worked. The long sad story of how we got to this point though is too complicated to keep retelling.

43. GoletaBeach says:

Well, the very high energy cancellations above the SUSY restoration scale are the bedrock prediction of the SUSY endeavor, and Nature doesn’t check in with any of us as to where to place that restoration scale. Nature also doesn’t care about the LHC or experimental budgets.

Burt Richter has always been right: theoretical physics is by and large a sociological activity, only a little different than theology or philosophy. You are making sociological observations. Only when incontrovertible data from experimentalists or observers test the theoretical guesses do theorists take notice, and often theorists find one of N wild papers they published and assert that they predicted it all. We’re going through an episode with Gordon Kane etc and everyone who went out on a limb about SUSY at the LHC. Oh well, the human drama.

As to your experience in the 1980s, well, you move in theoretical circles. You got sucked into the groupthink. Experimentalists were never anything but skeptics about SUSY… poor Mohammad Mohammadi and his SUSY discovery in the 1980’s at UA1.

Experiment also has sociological aspects, of course, and the drive to higher energy colliders has by and large been based on planning with a rear view mirror. Higher energies have worked before, so why not try again? There are of course other ideas… WIMP searches and indirect WIMP searches among them.

SUSY will always remain a reasonable motivation for all of them, forever.

As a field (including astrophysics) we’ve been interrogating dark matter since Opik in 1915 or so. Again, Nature doesn’t give a darn about human life scales. Secrets will be revealed when they are. Sociological sniping based on impatience is irrelevant.

As to nails in the coffin: it is a very large coffin and your nails don’t begin to cover its perimeters. You’re free to get bored with it, of course, but others may be more durable than you.

And on several occasions the search for neutrino mass/mixing was declared worthless and `over’ too. Thank goodness solid scientists carried on.

44. Chris Kennedy says:

I had this friend who called me a few months ago and said: “I ran some calculations and I’m pretty sure I have a ghost in my house.” Of course I thought he was kidding but he continued: “In exactly two weeks, I’m going to start hearing noises, and several items are going to get knocked onto the floor when no one is in the room.” So I went over to his house, we did a stakeout and we never heard a sound. He then said: “Well next week for sure” and this went on for three more occasions after that.

Even though he was the one who gave me the dates and times of all of the predicted supernatural “events” he then started saying things like: “Look, it’s a ghost, it’s going to come out when it feels like it – it’s certainly not obligated to our timetable.” I then asked him: “Did you ever consider the possibility that your house is not haunted after all?”

45. Low Math, Meekly Interacting says:

Forgive the naïve outsider, but the story of the search for neutrino masses doesn’t seem to me to be remotely like the story of SUSY. When you have a particle that demonstrably exists, a third of those particles emitted by the Sun are completely missing, there’s no particularly deep reason for it to be massless, and mass solves the missing neutrino problem, you’ve got some serious “motivation”. SUSY solves naturalness problems that might not even be problems, at the cost of an extravagant number of new particles that we’ve never seen, and which can remain forever hidden by breaking the symmetry at whatever scale remains conveniently unprobed. Where is the analogy?

46. Tim says:

I don’t know that a doubling is extravagant. In fact I’d personally say it’s more likely than a handful of new particles. Nature just sort of likes to do that.

Remember that antimatter doubled the number of known particles; generations tripled them for no obvious reason. Any broken symmetry is inevitably going to result in “… and this is the other half of the universe you didn’t previously know about.”

I can’t be the only who remembers Glashow’s answer to the likes of Tim’s argument. To paraphrase: SUSY must be right…after all we have already found half the particles it predicts.

48. Peter Woit says:

Tim,
What’s really suspicious here is that the theory says “all particles” will come in pairs of a specific kind, but if you look at the complicated structure of the many known particles, there are no pairs this kind. Not one. Another way of saying this is that the theory claims a new symmetry of nature. Symmetries tell us something by relating different states. SUSY provides no relations between any known states, it acts trivially on the space of known states (supposedly taking them to a different space).

And, unlike antimatter, introducing SUSY breaking to make the partners invisible means you’re not just postulating a doubling of the state space, with a Z2 symmetry, you’re also adding in a huge extra number of random parameters to deal with the SUSY breaking.

49. GoletaBeach says:

to Chris Kennedy… the only technique that guarantees certainty is to not look for new physics. They you are absolutely sure of the result… that nothing new will ever be discovered. If you want something new, there will always be risk of coming up emptyhanded.

to Low Math… the parameter space that describes possible neutrino masses and mixing angles is vast. No theorist had any prediction of which parameters Nature would pick. The solar neutrino experiment didn’t start as a neutrino oscillation experiment, it started because a clever experimentalist devised a technique with sufficient sensitivity to observe solar neutrinos. Most of the theoretical community didn’t support the experiment, and when there was a deficit, most of the theoretical community thought that poor solar models, not neutrino oscillation, was the explanation. A similar sequence played out with atmospheric neutrino oscillations. The heart of the matter is… experimentalists are generally at least as good and usually better at finding new physics than theorists. A good reason to keep doing WIMP and other dark matter experiments.

To Tim: yes, the tripling into three generations is an entirely unpredicted phenomenon, little considered. It often feels like there is a pattern of excitations underlying that one, but no substructure theories have ever been devised that help describe it. The usual contemporary attitude is that quantum field theory masks any underlying pattern so completely that it is pointless to look for a pattern. A good argument to complete the one pattern that is incomplete… the neutrino mass template. Maybe an interesting pattern will show up.

50. Low Math, Meekly Interacting says:

Hi, Goleta Beach,

Thanks for your reply. I’m far from expert in the matter, nor am I as knowledgeable as you about the history, by my understanding is that the first experiments back in the 1960s were designed to observed solar neutrinos because that’s an interesting thing to do. Beyond the related nuclear physics, theory didn’t really need to come into it. but they found the discrepancy (should have said 2/3, not 1/3 of the electron neutrinos missing), and that got the ball rolling in the right direction in short order. Of course people first suspected an astrophysical explanation. My understanding is that those speculations were dispatched without much difficulty, perhaps ironically by the temperature of solar neutrinos, which, among other results, showed that you couldn’t explain away the deficit through poor solar modeling. Reactor experiments, etc. gave a pretty tight upper bound on neutrino masses, the lower bound was assumed, so by the time people were looking seriously at neutrino mass, there were already very tight constraints.

Again, an experimentally verified particle, an experimentally verified and sizable deviation from theory, experimental elimination of the alternatives, and fairly inevitable experimental validation of the best explanation for the discrepancy. Which, perhaps to no surprise, has fostered advances in the field of neutrino physics that may provide the best hope for BSM theorists.

SUSY, rather, looks to me like the theoretical tail wagging the dog to death, and then continuing to wag the mutilated corpse in hopes flailing will resuscitate it. There’s no experimentally-validated anything to show unequivocally that it’s necessary, just a lack of understanding of the hierarchy problem. Which, as many smarter people than me continue to point out, we can’t say for certain is even a problem. And there’s no upper bound on the scale. There likely would have come a time when we could have said that the neutrino mass is so small that, if it exists, it couldn’t explain the solar neutrino problem. No such luck with SUSY. It’s already failed the “naturalness” test, LSP WIMPs are looking ever more implausible, etc., etc. It can live comfortably forever in the anthropic multiverse, which great for SUSY, I suppose, but hopeless scientifically. I just don’t see any comparison to neutrino masses at all.