The Rise and Fall of Supersymmetry

“Supposedly she’d died, but here she was again–somewhat changed, but you couldn’t kill her. Not when the truest part of her hadn’t even been born.” -Denis Johnson

Over the past 100 years, our picture of the Universe has changed dramatically, on both the largest scales and the smallest.

Image credit: Richard Payne.

Image credit: Richard Payne.

On the large-scales, we’ve gone from a Newtonian Universe of unknown age populated only by the stars in our own Milky Way to a Universe governed by General Relativity, containing hundreds of billions of galaxies.

Image credit: Rhys Taylor, Cardiff University.

Image credit: Rhys Taylor, Cardiff University.

The age of this Universe is dated at 13.8 billion years since the Big Bang, the observable part of which is some 92 billion light-years in diameter, filled with normal matter (and not antimatter), dark matter, and dark energy.

On the small scales, the revolution has been just as dramatic.

Image credit: 2011 Encyclopaedia Britannica.

Image credit: 2011 Encyclopaedia Britannica.

We’ve gone from a Universe made up of atomic nuclei, electrons and photons, where the only known forces were gravitational and electromagnetic, to a much more fundamental understanding of the smallest particles and interactions that make up the Universe. Nuclei are made up of protons and neutrons, which — in turn — are made up of quarks and gluons. There are two types of nuclear forces, the strong and the weak forces, and three generations of particles, including the leptons (electrons, neutrinos, and their heavier counterparts) and quarks (up, down, and their heavier counterparts). There are gauge bosons governing the strong, weak, and electromagnetic forces, and finally there’s the Higgs, bringing this all together under the framework of the Standard Model.

Image credit: Fermilab, modified by me.

Image credit: Fermilab, modified by me.

And combining the Standard Model of particle physics with General Relativity and the standard model of modern cosmology means that we can nearly explain the entire physical Universe! By beginning with a Universe that had slightly more matter than antimatter, and starting just some 10-10 seconds after the Big Bang, we can account for all of the observed phenomena using only the already-established laws of physics. We can reproduce — with simulations — a Universe that is, in all meaningful ways, physically indistinguishable from our own.

Images credit: 2dF Galaxy Redshift Survey (blue) and Millenium Simulation (red), in astonishing agreement.

Images credit: 2dF Galaxy Redshift Survey (blue) and Millenium Simulation (red), which agree!

And yet, there are some very fundamental questions we still don’t understand. Among them are:

  1. Why is there more matter than antimatter? Where did the asymmetry (of the observed magnitude) come from?
  2. What is the nature of dark energy? What is the field/property responsible for it?
  3. What is the nature of dark matter? What is the particle responsible for it?
  4. We know that, at very high energies, the electromagnetic and the weak force unify, and are actually a manifestation of the electroweak force, whose symmetry is broken at low energies. Do the other forces — the strong force and maybe even gravity — unify at some even higher energy?
  5. And finally, why do the fundamental particles — the ones in the Standard Model — have the masses that they do?

This last one is a problem known as the hierarchy problem in physics, and it goes something like this.

Image credit: © School of Physics UNSW.

Image credit: © School of Physics UNSW.

There are a few fundamental constants in nature: the gravitational constant (G), Planck’s constant (h or ħ, which is h/2π), and the speed of light (c). There are different combinations of these constants we can create to get values for time, length, and mass; these are known as Planck units.

Image credit: Mass-Energy Scale, via http://universe-review.ca/.

Image credit: Mass-Energy Scale, via http://universe-review.ca/.

If you were to predict the mass of the particles in the Standard Model from first principles, they ought to be on the order of the Planck mass, which has an energy of around 1028 eV. The major problem is that this mass is 17 orders of magnitude, or a factor of 100,000,000,000,000,000 larger than the heaviest observed particle in the Universe. The Higgs boson, in particular, should have the Planck mass, and — since the Higgs field couples to the other particles, giving them mass — so should all the others.

Image credit: Matthew J. Dolan, Christoph Englert, and Michael Spannowsky, via JHEP 1210 (2012) 112.

Image credit: Matthew J. Dolan, Christoph Englert, and Michael Spannowsky, via JHEP 1210 (2012) 112.

So why, we ask, do the particles have the mass that they do, and not much, much larger ones? The best, most elegant solution is that there’s an extra symmetry that cancels out all those Planck-scale contributions, and protects the mass down to a much lower energy.

Image credit: wikimedia commons user VermillionBird.

Image credit: wikimedia commons user VermillionBird.

That’s the idea behind Supersymmetry, known as SUSY for short. Supersymmetry makes the very bold prediction that every one of the Standard Model particles has a partner particle — a superpartner — that has nearly identical properties, except has a spin that’s different by a value of ‎±½ from its Standard Model counterpart.

Image credit: DESY at Hamburg.

Image credit: DESY at Hamburg.

This superpartner should protect the mass of all the particles — the Standard Model ones and the SUSY ones — all the way down to the scale at which SUSY is broken, at which point the superpartners acquire a heavier mass than the normal ones.

Image credit: © New Scientist.

Image credit: © New Scientist.

If SUSY is broken at the right scale to solve the hierarchy problem, somewhere between 100 GeV and 1 TeV, then the lightest supersymmetric particles should be accessible by the LHC.

But there’s more.

There are a bunch of things that are known not to happen in the Standard Model to very high precision: baryon number isn’t violated, lepton number isn’t violated, and there are no flavor-changing neutral currents. In order to make these things also not happen in SUSY, you need a new symmetry called R-parity, which comes along with an added feature. If R-parity is real and SUSY is real, then the lightest supersymmetric particle is stable, which means, if enough of them are left over from the hot Big Bang, it could be the dark matter!

Image credit: CDMS experiment, Fermilab / Dept. of Energy, via http://www.fnal.gov/.

Image credit: CDMS experiment, Fermilab / Dept. of Energy, via http://www.fnal.gov/.

There’s even one more cool thing that happens: if you take all the particles in the standard model, and you look at the interaction strength of the three forces, you’ll find that the strength of the forces — parametrized by their coupling constants — changes with energy. They change in such as way that, in the Standard Model, they almost meet at some high energy (around 1015 GeV), but just miss, slightly, if you put them on a log-log scale. But if you add in supersymmetry, the addition of these new particles changes the way the coupling constants evolve. And therefore, if SUSY is right, it could indicate a place where the electromagnetic, weak and strong forces all unify at a high energy!

Image credit: CERN (European Organization for Nuclear Research), 2001. Via http://edu.pyhajoki.fi/.

Image credit: CERN (European Organization for Nuclear Research), 2001. Via http://edu.pyhajoki.fi/.

In other words, there are three major problems that could all be solved by the existence of supersymmetry; it’s a great idea! (There are four if you count the problem of the Coleman-Mandula theorem, which many do, but I’m not one of them.)

But there’s also a few problems with each of these three problems that SUSY looks like it solves:

  1. If it solves the hierarchy problem, then there should definitely be new supersymmetric particles discovered at the LHC. In fact, if the LHC doesn’t discover supersymmetric particles, then even if SUSY exists, there must be some other solution to the hierarchy problem, because SUSY alone won’t do it.
  2. If the lightest supersymmetric particle is, in fact, the dark matter in the Universe, then experiments designed to see it, such as CDMS and XENON, ought to have seen it by now. In addition, SUSY dark matter should annihilate in a very particular way, which we haven’t seen. The null-detection status of these experiments (among others) is a big red flag against this. Plus, there are plenty of other good dark matter candidates as far as astrophysics is concerned; SUSY is hardly the only horse in the race.
  3. The strong force may not unify with the other forces! There’s no reason, other than our predisposition towards liking more symmetric things, for that to be the case. There’s also the issue that if you put any three curves on a log-log scale and zoom out far enough, they will always look like a triangle where the three lines “just barely” miss coming together to a point.

But the biggest failures of SUSY are not theoretical ones; they’re experimental.

Image credit: Geoff Brumfiel from Nature.

Image credit: Geoff Brumfiel from Nature.

And there are a lot of different ways of representing just how difficult it is to reconcile what SUSY expects with what we actually have — and haven’t — seen.

Image credit: Alessandro Strumia, via http://resonaances.blogspot.com/.

Image credit: Alessandro Strumia, via http://resonaances.blogspot.com/.

At the LHC, supersymmetric particles should have been detected by now, if they exist. There are plenty of theorists and experimentalists who are still optimistic about SUSY, but nearly all models that successfully solve the hierarchy problem have been ruled out.

Image credit: Particle Data Group (2012), O. Buchmueller (Imperial College London) and P. de Jong (Nikhef).

Image credit: Particle Data Group (2012), O. Buchmueller and P. de Jong.

At this point in the game, based on what we’ve seen (and haven’t seen) so far, it would be shocking if the LHC turned up evidence for supersymmetry. As always, continued experimentation will be the ultimate arbiter of nature, but I think it’s fair to say that the only reason SUSY gets as much positive press as it does is for two simple reasons.

  1. A lot of people have invested their entire careers in SUSY, and if it’s not a part of nature, then a lot of what they’ve invested in is nothing more than a blind alley. For example, if there is no SUSY in nature, at any energy scale, then string theory is wrong. Plain and simple.
  2. There are no other good solutions to the hierarchy problem that are as satisfying as SUSY. If there’s no SUSY, then we have to admit that we have no idea why the masses of the standard model particles have the value that they do.

Which is to say, SUSY or not, physics still has a lot of explaining to do, and there’s work to be done. But the biggest problem is that SUSY predicts new particles, and it predicts their existence to occur in a fairly specific range of energies.

Image credit: Matt Strassler of http://profmattstrassler.com/.

Image credit: Matt Strassler of http://profmattstrassler.com/.

If they’re not there, then this isn’t the right story. At this point, the theoretical hoops being jumped through to keep SUSY “viable” (and yes, that belongs in air quotes) given our experimental null results are getting progressively more and more extravagant. I’m not much of a betting man, but if I were, I’d say that SUSY is already dead. It’s just waiting for the coffin nails to be hammered in.

Comments

  1. #1 David Foster
    United States
    May 16, 2013

    Isn’t there a proven theorem to the effect that the only other symmetry possible, other than the ones we know about, is SUSY ?

  2. #2 Semmel
    May 16, 2013

    I can understand why the SUSY was as popular as it has been. But I never really got a good feeling towards it, neither do I have for Superstring theory. It just feels .. odd .. that the universe is hiding so much of its real existence. Like having 10 or even 20+ dimensions, but it shows us only 3. It feels suspicious to explain one mystery with an other one. http://physics.stackexchange.com/questions/6438/what-if-the-lhc-doesnt-see-susy I found a topic here, discussing the question “What if the LHC doesn’t see SUSY?” Yeah, what then?

    I am not a particle physicist, and I cant really judge the quality or viability of theories. For example http://en.wikipedia.org/wiki/An_Exceptionally_Simple_Theory_of_Everything Lisis work got a lot of media attention and I must admit that his idea seems quite beautiful. But despite all the reluctance of the science community to give this theory a chance.. wouldn’t a test be the right thing to do? So just do an experiment? After all, it predicts new particles, would it be possible to use the LHC to test it? (or support the theory, who knows?) After all, thats what the LHC is for, ruling out theories.

  3. #3 Douglas J. Bender
    Dickinson, ND (USA)
    May 16, 2013

    May I please, please, pretty please post a link to a video of the song, “Susie Q”? Please and thank you?

  4. #4 Douglas J. Bender
    Dickinson, ND (USA)
    May 16, 2013

    Oh, okay. I’ll take that as a “Yes”: http://www.youtube.com/watch?v=DWvHSF8aMzk .

  5. #5 Chris
    May 16, 2013

    So cognitive dissonance, in the minds of those scientists who’ve dedicated their lives to SUS, is keeping SUSY alive?

  6. #6 Jim Pivarski
    May 16, 2013

    “Isn’t there a proven theorem to the effect that the only other symmetry possible, other than the ones we know about, is SUSY ?”

    There is a theorem like that: the largest possible extension of space-time symmetry (Lorentz symmetry, which is the set of all translations, rotatations, and relativistic boosts) that is either made of commuting (a * b = b * a) or anticommuting (a * b = -b * a) variables is supersymmetry. This is particularly interesting because electromagnetism, the weak force, and the strong force are generated by non-spatial symmetries— relationships among abstract variables— while gravity is generated by the Lorentz symmetry mentioned above. Supersymmetry wouldn’t just quantitatively unify the strengths of electromagnetism, the weak force, and the strong force, it would also qualitatively unify some aspects of the first three forces with gravity. It’s no accident that supersymmetry is a necessary ingredient in string theory,

    One thing that’s rarely talked about these days is that the LHC can only probe weak-scale supersymmetry, the extension of supersymmetry that posits that it has something to do with electroweak symmetry breaking or naturalizing the Higgs mass (covered in the article above). Supersymmetry might still exist at the GUT scale and have nothing to do with weak scale physics— that was just physicists being greedy, trying to solve all problems with the same concept.

  7. #7 Angel Gabriel
    A quick question
    May 16, 2013

    In the 1st chart on the existing particle side.

    In the “parentheses” for quarks and leptons; it seems that the letter “L” is left off of the Quarks, u, c,and t and also left off of the Neutrinos e, mu and tau.

    I assume this is an error of omission and not some important information.

    Please advise/educate me

  8. #8 Wow
    May 16, 2013

    “It just feels .. odd .. that the universe is hiding so much of its real existence.”

    Most of existence isn’t there. Isn’t that odd too?

    Most of existence is determined by the possibility of existence. Isn’t that odd too?

    The most likely place to find a quantum sized ball in an energy pit is in the centre, not the edges as you find in the macro scale world. Isn’t that odd too?

    Beware of a reality perceived based on 1 part in 10^30th of the scale of the universe and light waves that comprise 1 part in 10^12th of the possible spectrum.

  9. #9 OKThen
    Emergence or other major adjustment
    May 16, 2013

    Just a few comments

    Very nice summary. Yes, I particularly like the 5 “fundamental questions we still don’t understand.”

    But the problems with SUSY are equivalent to the problem with DM, DE.

    By that I mean that SUSY type models are the only ones that I am aware of trying to extend the Standard Model of Elementary Particles.

    But, “In particular, the Standard Model cannot explain the observed amount of cold dark matter (CDM) and gives contributions to dark energy which are many orders of magnitude too large. It is also difficult to accommodate the observed predominance of matter over antimatter (matter/antimatter asymmetry). The isotropy and homogeneity of the visible universe over large distances seems to require a mechanism like cosmic inflation, which would also constitute an extension of the Standard Model.” wikipedia

    So it seems that without an alternative to the Standard Model of Elementary Particles; that the Standard Model of Cosmology is in big trouble.

    OR, BIG OR, the “dark matter observations” and “dark energy observations” may be due to some kind of emergent particle of phenomenon.

    Suggesting that if the Standard Model of Elementary Particles is all that there is; then the “hypothetical graviton” and “hypothetical dark matter” may be an emergent particle, and the hypothetical “dark energy” may be emergent phenomenon.

    By emergent, I mean something like a phonon particle/phenomenon.
    “In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, such as solids and some liquids. Often referred to as a quasiparticle,[1] it represents an excited state in the quantum mechanical quantization of the modes of vibrations of elastic structures of interacting particles.” wikipedia

    I didn’t hear Ethan mention any possible extensions to the Standard Model of Elementary Particles except the various SUSY type extensions. Are there non-SUSY types of extensions. Please give an example and link.

    As for the “biggest (experimental) failures of SUSY” discussion and charts. Well said Ethan.

    But Ethan, where is your “biggest experimental failures of DM and DE” discussion and charts?

    If the Standard Model of Elementary Particles is right; then the Standard Model of Cosmology is wrong.
    If the Standard Model of Cosmology is right; then the Standard Model of Elementary Particles is wrong.

    My bet; they both need some major adjustment.

  10. #10 Wow
    May 16, 2013

    “and gives contributions to dark energy which are many orders of magnitude too large.”

    Only if the source of dark energy is the total possible from the non-zero energy point based on Quantum Mechanics.

    There have been threads on experimental problems with DE/DM and MOND and MACHOs and WIMPS.

    The conclusion has generally been “they’re all incomplete. but DE/DM is in much less trouble as a sole source than any of the others”.

    I.e. “It’s the worst explanation apart from all the others”.

  11. #11 CB
    May 16, 2013

    The biggest experimental failures of DM are comparatively trifles — specific individual galaxies or clusters where the failure could simply be a lack of understanding of the specific dynamics at play (e.g. how the Pioneer Anomaly played out).

    The experimental successes are massive. In particular the successful prediction of the Power Spectrum of the CMB as measured by WMAP and Plank is a success almost as great as the original prediction of the CMB by the Big Bang Theory.

    Compare with SUSY, which has zero successes. The only table of experimental results possible is a table of failures. It might still be true, but we’ve already ruled out it being true in regimes where it solves the problems it was proposed to solve.

    This would be somewhat like if the CMB said that taking into account the error bars Dark Matter might exist, but not in quantities sufficient to explain galaxy and cluster formation and behavior. However that is not the case. Instead these separate measurements from completely separate phenomenon result in very close agreement.

    So the equivalent article for DM would basically be “The tremendous experimental successes of DM (with some caveats)”. An article which Ethan has already written (several times). As usual your request that different things be treated as if the same is misguided.

    SUSY is not the only model for extending the Standard Model. There are plenty of others (Ethan has written about them before, too).. The reason you’ve only heard of SUSY is because of the reasons Ethan said: A relatively simple extension to the SM could solve multiple problems at once, and is also inherent in our very best attempt at a GUT so far, String Theory.

    So it’s a very nice hypothesis and one favored by many physicists, not without reason. But it’s failures are not DM’s failures. Failing to detect SUSY particles that could be DM candidates just means SUSY probably can’t solve the problem of DM, just like it’s failing to solve the hierarchy problem.

    The Standard Model is already known to be “wrong” in the sense of being incomplete. It doesn’t explain all phenomenon, and doesn’t explain where certain values come from, etc.. So that ship has already sailed.

    On the other hand, there has yet to be a single hint that the Standard Model is wrong in the sense of giving an incorrect prediction on something it does predict. It can’t tell you why the known particles have the masses they do (and it should), but once you plug those values into the equations the result matches experiment exactly.

    So the big problem with a “major adjustment” to the Standard Model is that it still has to give the same results within the regime (energies and precisions) in which the SM has been already tested. The SM simply isn’t wrong in that regime. Again, another reason why SUSY is popular.

    Can the Dark Matter problem be solved via emergent properties of the existing Standard Model? Maybe. Getting one that matches the observed properties of Dark Matter is a trick — especially the CMB peaks — but it’s worth trying.

    Of course if it did work, then that would just mean that DM was whatever this emergent property is that ends up behaving very much like WIMPs, rather than a new WIMP itself. We already have strong observations of that behavior that won’t go away, so the only option for an alternative is to produce the same answer.

    Why you’d favor that solution over others, if you’re going by experimental success, is unknown to me.

  12. #12 CB
    May 16, 2013

    Wow said: I.e. “It’s the worst explanation apart from all the others”.

    Jeebus. As usual I write a book while someone else makes a point of equal or greater sharpness in one sentence.

    So here’s my attempted re-write of the book with a similar eye to brevity:

    False equivalence is false.

  13. #13 CB
    May 16, 2013

    By the way, here’s a coincidink: I was just reading Matt Strassler’s article about SUSY where the picture at the end of this post appears. Which means I know why he has quotes in Symmetry “Breaking” — cus part of that article was explaining that “symmetry breaking” is a somewhat misleading term for what’s really “symmetry *hiding*” — the symmetry still exists, but you don’t notice for some reason.

    His example: The laws of physics are rotationally symmetric, but standing on the surface of the earth this doesn’t appear to be the case because there’s a definite difference between “up” and “down” and “sideways” thanks to the gravitational field.

    I found this interesting so I just thought I’d share.

  14. #14 Wow
    May 16, 2013

    I’ve got away with words.

    (see what I did there?)

  15. #15 Torbjörn Larsson, OM
    May 16, 2013

    Since the article is using one of Strassler’s images, I think it is pertinent to point out that Strassler, a former LHC particle physicist, disagrees with that SUSY should have been detected or that LHC has ruled it out:

    “Among the many goals of the LHC is to find or rule out supersymmetry at the TeV scale. (It cannot hope to rule out supersymmetry altogether; that would presumably require a vastly more powerful collider that won’t likely be built for centuries, if ever.) It’s not enough to rule out the CMSSM, or the NUMH1, or even the MSSM. Similar statements apply for other speculative ideas that propose as yet unknown particles and forces; it’s not enough for the LHC to rule out just the simplest variants of these ideas.”

    If LHC does rule out TeV scale SUSY and it won’t solve the hiearchy problem, there is evidently a natural candidate that allows string theory and its landscape to produce inflation:

    “A rather different possibility, which has been around for a long time and which Arkani-Hamed likes (and I used to not be very fond of, but the Higgs mass measurement forces me to pay it more attention), is that supersymmetry does not entirely solve the hierarchy problem, but solves it part-way, with the remainder explained by a lucky accident or though a selection bias (such as the “anthropic” or “structure” principle, whereby the reason our part of the universe looks unusual is that (a) the universe is much more immense and diverse than we realize, (b) most regions are uninhabitable, and (c) only in rare regions with very unusual properties can there be anything like stars, planets, and evolution.)

    This is the notion of “split supersymmetry”, whereby the fermion superpartners of the photon and the W, Z and Higgs particles remain relatively light and LHC-accessible, while the boson superpartners of the matter fermions are heavier by about a factor of 100 or more. (This kind of splitting arises very easily in theories of supersymmetry breaking, and in fact one typically has to work to avoid it.) A complete solution to the hierarchy problem is abandoned, but it turns out this idea has some nice features too, which I’ll skip (but see Figure 1).”

    [My bold; the p"nice features" is that SUSY gives DM and unification, while it avoids the problems of standard particle and string theory.]

    So it’s not natural in the TOE sense of O(1) parameter values, but it is natural in the “no finetuning” sense – the finetuning is what inflation gives. In fact, freezing out first the SUSY DM sector and then the standard particle sector is just what Susskind’s tree models of eternal inflation ordered.

    In fact, I think split supersymmetry & inflation predicts pretty much everything except matter/antimatter broken symmetry in the layman sense, I’m pretty sure there are remaining problems.

  16. #16 Torbjörn Larsson, OM
    May 16, 2013

    @David Foster: “a proven theorem to the effect that the only other symmetry possible”

    Isn’t that the Coleman-Mandula theorem of the article, SUSY’s ability to mix internal and external degrees of freedom as I understand it? (But see Pivarski’s comment.)

    @OKThen:

    “the problems with SUSY are equivalent to the problem with DM, DE.”‘

    No, youy are as wrongly wrong as any wronger can be:

    First WMAP and then Planck has conclusively tested all of standard cosmology including DE and DM. DE and DM has numerous successful observations and a well tested theory.

    SUSY is still unobserved.

    Give it up, handwaving arguments from incredulity isn’t helping you either understand the topic or convince others in it.

  17. #17 Ethan
    May 16, 2013

    Torbjörn,

    This is one of the only points where Strassler and I vehemently disagree. “Split SUSY” would be justification for a next-gen collider, but how “split” is it? 100 TeV? 100 PeV? All the way up at the GUT-scale? (10^15 GeV?) The “work to avoid” split SUSY requires some pretty bold assumptions about the physics of new particles; these are exactly the progressively more extravagant hoops I was warning about.

    The no-finetuning-necessary-because-of-inflation argument is completely untrue; Susskind is virtually a non-player when it comes to the development of eternal inflation. (That would be Guth, Tye, Erick Weinberg, and Linde, as far as I’m concerned.) Again, the hugest problems with SUSY are the flavor-changing-neutral-currents, which one must fine-tune to avoid, and the only way to avoid them is to push them up to energies so high that the hierarchy problem isn’t solved at all. The “little Higgs” or “Fat Higgs” models that address this, again, predict new particles that the LHC should see.

    If that was tl;dr: You are being sold a lemon.

  18. #18 Ethan
    May 16, 2013

    I should clarify: even in split SUSY, the fermions (the neutralinos) should be LHC-accessible. Not finding them should falsify all claims of TeV-scale SUSY, including split-SUSY.

    The rest of what you’re being sold is a non-falsifiable lemon, akin to Russell’s teapot. Strassler is being far too kind to SUSY, IMO.

  19. [...] Supersymmetrie eine schöne Erweiterung der Physik wäre, aber es wohl doch nicht ist – weniger wegen theoretischer Probleme als vielmehr des komplett ausgebliebenen Nachweises [...]

  20. #20 Alan L.
    May 17, 2013

    @Ethan

    And combining the Standard Model of particle physics with General Relativity and the standard model of modern cosmology means that we can nearly explain the entire physical Universe!

    Well, about 4% of it.

    There are plenty of theorists and experimentalists who are still optimistic about SUSY, but nearly all models that successfully solve the hierarchy problem have been ruled out.

    And:

    … there are no other good solutions to the hierarchy problem that are as satisfying as SUSY.

    And:

    For example, if there is no SUSY in nature, at any energy scale, then string theory is wrong. Plain and simple.

    No arguments from me on the SUSY side. It’s not as disgracefully absurd as the perpetually splitting multiverse theory.

    The Randall-Sundrum warped geometry theory provides an elegant non-SUSY solution to the hierarchy problem. However, it would require accepting the possibility that at least three additional large spatial dimensions exist, linked to our familiar three dimensions via two “branes”, known whimsically as the p-brane and the weak brane.

    Although R & S were not adventurous enough to go as far as to suggest a new particle as a means or conduit that would enable the gravitational force to leak into our familiar three-space from other dimensions, would you, using accepted and orthodox scientific doctrines as your firm foundation, consider devoting a future post trying to demolish the R-S theory?

  21. #21 Wow
    May 17, 2013

    “Well, about 4% of it.”

    By weight or volume?

  22. #22 John Duffield
    May 17, 2013

    Good article, Ethan. I picked up on: “we have no idea why the masses of the standard model particles have the value that they do”. There are people who have made “quantum harmonics” proposals about this, but the trouble is that they don’t just make SUSY redundant, they upset the SM too. There are clues if you’re sharp. In the wiki Atomic Obitals article you can read “The electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves”. You can make an electron (and a positron) in gamma-gamma pair production, wherein a field-variation becomes a standing field. You can diffract the electron, it’s got a magnetic moment, and the Einstein-de Haas effect demonstrates that “spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics”. The electron isn’t some “fundamental particle”, it’s a spin ½ standing-wave configuration with a particular topology and a 4π spherically-symmetric electric field, wherein c and h dictate that only one wavelength will do. You know that Planck length is l=√(ћG/c³). Replace =√(ћG) with 4πn where n is a suitable value. You’ve still got that Planck length. Now set n to 1 and work out 4πn/c^1½. There’s a bit of binding energy adjustment to make related to the g-factor, but not much.

  23. #23 Wow
    May 17, 2013

    However, for the momentum described by that spinning electron, at the size it MUST be less than (because it acts like a point to anything with a wavelength of that size), the equator of the electron would have to be moving faster than light.

    So it can’t be “macro-scale” spin momentum.

    However, as a model of whatever it is actually doing, thinking of it that way and ignoring the ways it can’t works really well to describe what will happen when you interfere with it.

    Which is somewhat analogous to the meta-labels Dark Matter and Dark Energy (I’m happy with their use as labels for “a set of observational characteristics that we could describe as anomalous activities in the universe”). What they are is not yet known, what the effect of whatever group of changes they are have to match the observed criteria.

    Even MOND, despite not being “Matter” would have to do this and I would accept that as an interim, it comes under “Dark Matter” because if MOND were the entire answer, it would have to display the characteristics given to Dark Matter.

  24. #24 Bob
    May 17, 2013

    Its funny how Ethan claims supersymmetry is dead and is ruled out by experiment, but then goes on to say that high scale supersymmetry is unfalsifiable.

    So its falsified when it suits Ethan, and unfalsifiable when it suits him.

    Hmm, is Ethan Peter Woit’s pitbull? Claiming that a theory is ruled out by data, but also not even wrong.

    What is sad is how ridiculously contradictory Ethan’s whole argument is, and yet he is totally oblivious to the fatal flaws in his own arguments, and promotes it to everyone.

  25. #25 Wow
    May 17, 2013

    Bob, funny how you complain what Ethan says, but HAVEN’T READ WHAT HE SAYS.

    There’s no solution to SUSY that ALSO solves the heirachy problem.

    Please, before crowing over someone else’s idiocy, make sure you’re not exponentially more idiotic yourself, hmmm?

  26. #26 John Duffield
    May 17, 2013

    Wow: re the equator of the electron would have to be moving faster than light. So it can’t be “macro-scale” spin momentum. That’s a non-sequitur* I’m afraid. The electron doesn’t spin like a planet. It isn’t some billiard-ball thing. See Dirac’s belt at http://www.mathpages.com/home/kmath619/kmath619.htm and note this: “In this sense a Mobius strip is reminiscent of spin-1/2 particles”. The Mobius strip exhibits a half-twist per turn. The minor-axis rotation is at half the rate of the major-axis rotation. Think in terms of one rotation at c and another rotation at ½c rather than a single planar rotation at c^1½.

    There’s a halfway house between Dark matter and MOND. Let’s talk about that when Ethan does a relevant blog.

    * See Stern-Gerlach on wiki and you can find this in a 2011 historic version, but not on the current version.

  27. #27 Wow
    May 17, 2013

    “Wow: re the equator of the electron would have to be moving faster than light. So it can’t be “macro-scale” spin momentum. That’s a non-sequitur* I’m afraid.

    Maybe. For the point you wished to be primary.

    However, the point I wished to make was regarding the reification of momentum.

    and the Einstein-de Haas effect demonstrates that “spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics”

    In classical mechanics, the electron would have to be spinning faster than light. Ergo, your assertion there is based on effect, not reality.

    I.e. reification.

  28. #28 CB
    May 17, 2013

    Ben: “Its funny how Ethan claims supersymmetry is dead and is ruled out by experiment, but then goes on to say that high scale supersymmetry is unfalsifiable.”

    Ethan: ” nearly all models that successfully solve the hierarchy problem have been ruled out.”

    Ethan: “Not finding them should falsify all claims of TeV-scale SUSY, including split-SUSY.”

    The mind boggles at how selective your reading would have to be to arrive at your interpretation.

    The mind chortles at you using “when it suits him” to mean “when discussing a specific (and explicitly stated) context in which the statement is true”. Ignoring context to force illogical statements into other’s mouths is classic weasel-speak.

  29. #29 John Duffield
    May 17, 2013

    @Wow: In classical mechanics, the electron would have to be spinning faster than light. No it wouldn’t. It just has to have a biaxial spin. You’ve fallen for the non-sequitur again, which starts with if the electron spins like a planet. It doesn’t spin like a planet. Planets do not exhibit spin ½.

  30. #30 John Duffield
    May 17, 2013

    @Wow: In classical mechanics, the electron would have to be spinning faster than light. No it wouldn’t. It just has to have a biaxial spin. You’ve fallen for the non-sequitur again, which starts with if the electron spins like a planet. It doesn’t spin like a planet. Planets do not exhibit spin ½.

  31. #31 Wow
    May 17, 2013

    Yes it would.

  32. #32 Wow
    May 17, 2013

    And what the fuck is “bi-axial spin”????

    If you have a sphere and set it spinning then add another axis of spin, you now have ONE AXIS OF SPIN which is the resultant vectors of both.

    Shit, and it looked like you knew what the hell you were talking about too. Shows how wrong you can get, I suppose.

  33. #33 OKThen
    The rumor of supersymmetry's death is greatly exaggerated!!
    May 19, 2013

    Of course, “dark matter observations” could be due to either a particle or general relativity or MOND or quantum gravity. I mean when after 80 years of trying to explain a result, with no definitive explanation; well it is best to keep one’s options open.

    But that seems to open for the “dark matter” has to be a particle folks. And some of those, it’s got to be a particle folks seem to be getting very frustrated with their necessary messengers exploring particles.

    Yes, that’s right; let’s shot the particle physics who can’t find the particle that we want them to find. And since a primary candidate for a “dark matter” particle is a WIMP particle; let’s shoot the supersymmetry theory!

    Fortunately the experimental physicsists looking for WIMP have not shoot the supersymmetry thoery (at least not all of the varieties of supersymmetry)

    Dark Matter Search Results Using the Silicon Detectors of CDMS II, Apr 15, 2013 http://cdms.berkeley.edu/CDMSII_Si_DM_Results.pdf
    “There is now overwhelming evidence that the bulk of the matter in our universe is in some nonluminous, non-baryonic form. Weakly Interacting Massive Particles (WIMPs) form a leading class of candidates for this dark matter… After unblinding, extensive checks of the three candi-date events revealed no data quality or analysis issues that would invalidate them as WIMP candidates. The signal-to-noise on the ionization channel for the three events (ordered in increasing recoil energy) was measured to be 6.7, 4.9, and 5.1, while the charge threshold had been set at 4.5 from the noise.”

    Well excellent research searching for a fallen supersymmetry particle!!

    The rumor of supersymmetry’s death is greatly exaggerated!!

  34. #34 OKThen
    oops, sogma's didn't copy through
    May 19, 2013

    sorry the sigma’s didn’t copy through. that is.
    “6.7sigma, 4.9sigma, and 5.1sigma, while the charge threshold had been set at 4.5 sigma.”

    http://www.huffingtonpost.com/2013/04/15/dark-matter-found-underground-detector-particle-physicists_n_3086829.html

    My bias is that some kind of quantum gravity will explain both DE and DM.

    But I’m keeping an open mind until I hear the fat lady to sing

    And if this excellent supersymmetry WIMP particle research holds up to scrutiny; well I’ll be as happy as a Higgs boson.

  35. #35 Wow
    May 19, 2013

    ” I mean when after 80 years of trying to explain a result, with no definitive explanation; well it is best to keep one’s options open.”

    Did you not read it? You appear to have but also appear not to have.

    Dark Matter IS the open option.

    MOND doesn’t fit.
    MACHOs don’t fit.

    Just because you keep your options open DOES NOT mean you get to keep open the options that have been tested AND FAILED.

  36. #36 OKThen
    A very big window
    May 19, 2013

    Just because one supersymmetry option has failed doesn’t mean they all have failed.

    I don’t like MOND either; but just because one or many have failed doesn’t mean they all have failed. Here’s MOND still being evaluated
    Testing MOND with galaxy-galaxy gravitational lensing, Mordehai Milgrom, May 2013.
    While I’m not buying it; until the fat lady sings; the MOND folks will continue offering their best idea.

    What exactly is your best idea Wow?

    So, yes keeping options open means keeping open the options that still fall within the windows experimental/theoretical possibility.

    Because to capture a very elusive (for 80 years now eluding) tiny hidden elusive fly (i.e. particle or modification to theory) called the explanation(s) of the “dark matter observations” we need to keep open a very big window.

  37. #37 Wow
    May 19, 2013

    And just because MOND is tried doesn’t mean you can whine about it being off the table.

    Whatever it is, it has to ACT as if there were a mostly homogenous mass of non-interacting particles spread throughout the universe a’ la Dark Matter.

    If you want to slide something in there, stop bloody whinging and work it out. If that is beyond you, shut up about it, OK? It’s bloody idiotic. If you’re not going to take Ethan’s workings and can’t do your own, go and find someone who will and bother THEM.

  38. #38 OKThen
    What we don't know is not known
    May 20, 2013

    Wow
    It is you who are whining.
    Fact is there are excellent “dark matter observations.”
    Fact is no successful interpretation has been worked out yet.

    a) if it is a particle of some type, no one knows what it is
    b) if it is a new interpretation of theory or new theory, no one knows what it is

    With that state of affairs, it is very presumptive to assume the only answer is a) and not b)

    This isn’t about Ethan, Wow, of OKThen’s theories. It is about the excellent research that is currently being done to explain the “dark matter observations”.

    And my quotes are not meant to scare.

    When the particle physicists agree that we have inCERN found an appropriate particle that explains dark matter; well then we will have a dark matter particle.

    It works very easy, now we have a Higgs particle; not a hypothetical Higgs particle.

    We also now have gravity but not a “hypothetical graviton”; nevertheless we do have a theory of gravity.

    Status of supersymmetry is “hypothetical”.

    You see, dark matter theory is not religion; proclaiming there to be dark matter particles does not make it so. We don’t know. So the scientific thing to say is we don’t know. We don’t know about supersymmetry either.

    It is a very worthy idea that dark matter observations will be explained by
    a) some type of new particle
    b) some new interpretation or theory
    But we dobn’t know.

    And we don’t know about supersymmetry either

  39. #39 Wow
    May 20, 2013

    “Wow
    It is you who are whining.”

    Yeah, like when someone tells somebody else who is making a racket complaining about their train seat is “complaining”.

    I.e. if you’re retarded or willingly obtuse, you can insist you’re right, but in standard nomenclature, you’re full of shit.

  40. #40 CB
    May 20, 2013

    OKThen: “Yes, that’s right; let’s shot the particle physics who can’t find the particle that we want them to find. And since a primary candidate for a “dark matter” particle is a WIMP particle; let’s shoot the supersymmetry theory!”

    What the heck are you on about now?

    Do you know what it’s called when someone who favors the WIMP hypothesis points out that the most promising theoretical candidate for WIMPs aren’t showing up in the region where they’d solve the problems they were designed for?

    Honesty.

    “With that state of affairs, it is very presumptive to assume the only answer is a) and not b)”

    Feh. Nobody is assuming the answer is “a and not b”.

    However many are correctly stating that the WIMP hypothesis is far and away the current best hypothesis by virtue of making astoundingly powerful and correct predictions. The predicted effect of WIMPy DM on the CMBR power spectrum was clearly and unambiguously found in the WMAP and Planck data, and the amount of DM indicated matches that found by indicated by all the other completely different lines of evidence. Other hypothesis can’t even come close to this.

    Do you know what it’s called when you ignore this fact in order to create a false equivalence that every non-completely-verified and non-completely-eliminated hypothesis has an equal shot at being correct despite existent experimental evidence that says otherwise?

    Dishonest and pathetic.

    You can have a preference while still being honest about the evidence for it. That’s what Ethan is doing. You should try it.

  41. #41 Wow
    May 20, 2013

    There are others out there trying to find out how to modify MOND (for example) to fit, so going there and finding out what problems they’re encountering and how they’re fixing them (and a pro tip: if they’re ignoring the problems and not trying to fix them, they’re not doing science), then you can find out the current state-of-the-art of trying to rescue $FAVOURED_THEORY.

    Meanwhile, I hold out against WIMP dark matter because nobody has a concrete clue of what sort of WIMP it is, why it turns up, and how we can tell if that is it, I just reserve judgement. That doesn’t mean I hold out for MOND, since that’s broken.

    What I am more open to is that some modification to gravity or newtonian mechanics may make the inexplicable-by-pure-WIMP features of dark matter fall out much more correctly. Or that a MOND may mean that 90% of “DM” is WIMP and 10% MOND.

    But someone coming up with a MOND has the same problem in those cases that WIMPs do: explain what it is, why it comes about and how we can tell.

    And to that extent, MOND is still a nonentry.

    Add that to the problem that MOND cannot explain the observations unless you’re evidently just curve fitting, and it’s on the kerb.

  42. #42 Torbjörn Larsson, OM
    May 27, 2013

    Ethan, I didn’t get back to this right away:

    I appreciate the response! But Strassler and Arkani-Hamed are the particle physicists, they don’t think it is “hoops”. (And the figure says “no flavor … problems”, whatever that means if not what you describe.) So I don’t necessarily agree on lemon.

    And on testability, we won’t agree. Inflation has been tested for it already, Weinberg’s cosmological constant work which succeeded.

    However, in another comment you have mentioned that you want explicit inflation process dynamics. It seems the Planck results on its potential is not enough for you, it is too sketchy? I don’t think there is a consensus on that, people has worked on that potential from WMAP and on. (In this context I have even seen an article how the flat plateau has implications for non-standard particles.)

    Yes, I know Susskind and the other scientist’s those work he references is an inflation non-player. But it is a possible theory, and a non-split SUSY is not looking good, so it was worth mentioning that if you let the TOE “natural” idea go, it is replaced with natural inflation theories.

  43. #43 Torbjörn Larsson, OM
    May 27, 2013

    Or, I should say on Susskind, he plays with Bousso, which is prolific and a player on eternal inflation.

    [Speaking of players as you like to do, Linde is good, but his chaotic inflation is more or less excluded by Planck now, isn't it? Meaning, even players can bet on the wrong horse.]

  44. #44 mark
    July 18, 2013

    I like the symmetry this shows, and the possibilities

    http://chemicalforum.webqc.org/viewtopic.php?t=18676

  45. #45 Jamahl Peavey
    Massachusetts
    August 1, 2013

    Great News: New Physics was discovered and reported by three or more sources. Sofia Technical University of Bulgaria conferenced it, Indian Journal of Science and Technology published it, and Anne’s Astronomy News gave it to the international public. Binary star moition was successfullty linked on all major quantum structures. What is sad is many of those who are crying about SUSY know about the paper and its success. Including the author of “Cracking the Einstein Code”. Here it is:

    http://annesastronomynews.com/double-stars-mysterious-connection/

  46. #46 Kevin Dowd
    August 28, 2013

    well maybe Ethan is on vacation.. I hope he takes a look at your paper.. at least it is published and it has equations!

  47. #47 Wow
    August 29, 2013

    OK, another link to a report with two options:

    1) The paper is crud
    2) The reporting on the paper is crud.

    Double stars are NOT more massive than our sun and not the size of cities.

    Neutron stars are more massive than the sun and the size of cities.

    They aren’t the same thing as double stars.

    Searching for gravity waves, they are looking for high-energy emitters of gravity waves and massive objects moving fast in a circle (therefore have to be close to each other) are the best sources, and therefore they look for double stars made of neutron stars.

    The reporter or the author of the paper is seriously deluded on this VERY VERY basic point and therefore I discard the paper based on the report of this devastating error in begins with.

  48. #48 dean
    August 29, 2013

    The paper seems to have an interesting source. The reported author is given as

    Mr. Jamahl Peavey,
    Physics and Mathematics Instructor/Mechanical Engineer at
    The Arlington School, Department of Physics,
    115 Mill Street, Belmont, MA 02478.

    but a search for that school returns only this:

    http://www.thearlingtonschool.org/

    in which the school is described as a private college prep school for students with “academic, social, and emotional challenges”, with a strong reputation for academics. However, I could not find any descriptions of the offered classes: the closest I could find was a link to a “sample schedule”. However, when I followed that I was taken to the Apple start page.
    Something seems fishy.

  49. […] string theory. Although there currently isn’t any experimental evidence to support string theory, and some evidence pointing against it, it still garners a great deal of attention because of its perceived theoretical potential. One of […]

  50. #50 Alma
    December 20, 2013

    Hi Ethan,
    The content on this page is owned by you, so I will ask for your permission to copy a part of the article to Wikipedia. You explain beautifully and with great clarity why was there SUSY in the first place and this clarity is missing from the article. Do I have your permission? Otherwise I will have to adapt it but I’m afraid not the ruin the qualities I appreciate most. As an alternative, I invite you to help improve the SUSY dedicated page; the community will benefit greatly from your support.
    Thank you!

  51. #51 Ethan
    December 20, 2013

    Alma,

    As far as I’m concerned, you do not need my permission; you can simply do that if you like. As long as you cite me, you should be fine in everyone’s eyes.

  52. […] any attempt to resuscitate it now appears rather hopeless. Part of the story is summarized in this blog as well as in a recent high precision measurement of the electron dipole […]

  53. […] At beyond 10-9 we’re at the size of an atom.  I’m going to borrow some images from “The Rise and Fall of Supersymmetry” at ScienceBlogs to help […]

  54. […] for Dark Matter Signal Strengthens. But please keep in mind The Rise and Fall of Supersymmetry (an old post from Ethan Siegel).      […]

  55. #55 Mark A. Thomas
    Memphis, Tennessee USA
    March 5, 2014

    You just ressurected this to your new Medium page which looks cool by the way. It looks if there is any SUSY at all she is going to be Hot Dense SUSY near the Planck energy. Too bad for direct observation and future colliders. But theory will find a way. I say if the Chinese want to build the 100 TeV collider and pay for it then lets look forward to that even if we just witness a very large particle desert from that.

  56. #56 Ethan
    March 5, 2014

    :-)

  57. #57 PJ
    March 6, 2014

    @48, Dean

    Try this :-
    http://www.uta.edu/physics/

  58. #58 Wow
    March 6, 2014

    I thought this was because someone put it up at slashdot recently.

  59. #59 Jesse M.
    March 7, 2014

    Just to be clear, is the experimental evidence ruling out supersymmetric theories in general, or just supersymmetric theories that purport to solve the hierarchy problem? If the latter, maybe the explanation for the widely varying particle masses is just an anthropic one that says particle masses vary in all sorts of ways throughout the multiverse (due to spontaneous symmetry breaking happening in different ways in different regions, leading to different vacuum states), but only certain types of variations are compatible with life? In this case, even if supersymmetry wouldn’t explain the hierarchy problem it could still make sense of the graph that shows that when you plot strength as a function of energy for the EM force and the strong and weak nuclear forces, they almost meet up at a single point but not quite, since with supersymmetry added the meeting becomes exact. Speaking of which, another question: are there any non-supersymmetric theories that purport to unify the strong force with the electroweak force, and are there any non-supersymmetric versions of string theory that can unify gravity with the other 3 forces?

  60. #60 Michael
    Pittsburgh, PA
    April 28, 2014

    Ethan,

    I know that LHC has also been searching for SUSY superpartners like they have looking for the Higgs (i.e. looking for missing energy & not necessarily a visible particle per se.

    What if our whole approach is wrong. In QM virtual particles aren’t required to be “real” Actual interaction in a Feynman diagram can be construed so to do something that if were viewable would violate causality though since virtual the interaction is not forbidden.

    So could be that superpartners can not be viewed in any direct way and can only be present in a “virtual” way. This would open the requirements on what a potential SUZY type particle could look like.

    Just wondering. I am not sure if this blog is still running.
    I thought maybe since the SciAm article came out this month that it might start up again.

  61. #61 Zephir
    http://aetherwavetheory.blogspot.cz/
    April 28, 2014

    IMO whole this discussion is nonsensical, as the SUSY was already observed at LHC in form of five Higgses i.imgur.com/dhUsUAq.gif

  62. #62 Michael
    Pittsburgh, PA
    April 29, 2014

    FInding the Higgs does not guarantee being able to find any of the superpartners Fermion/Boson type. The conventional wisdom is that near TeV some/most would have been seen. Thus some assumption is off or the theory is either incomplete or wrong. I am confident SUZY may win out in the end. Discussion seems to be focusing on “neutrolinos” of some type.

  63. #63 Michael Kelsey
    SLAC National Accelerator Laboratory
    April 29, 2014

    @Zephir #61: Um, really? The two main LHC experiments (CMS and ATLAS), have reported observing a _single_ resonance at 126 GeV, with spin-parity 0+, consistent with being the Standard Model Higgs boson.

    *NO* observation of any other putative Higgs multiplets have been reported, only upper limits on their (non-)existence, or equivalently, lower limits on their masses.

    I don’t know where you got the plots you “attached”, since you don’t provide any sort of citation to peer reviewed literature. I can tell you that no particle physicist would fit mass peaks to a “fourth order polynomial”, since the proper shape for a simple resonance in experimental data is a Briet-Wigner (the true relativistic shape) convoluted with a Gaussian (for experimental resolution). If the true width is much narrower than the resolution, then a simple Gaussian is good enough. A polynomial is utter crap, and demonstrates that whomever is playing with that data is most likely either a crackpot or simply ignorant of the relevant science.

  64. #64 Jacques
    Toulouse, France
    May 16, 2014

    I guess everyone believes there is a hierarchy problem, and that SUSY is the best solution. Indeed I think there is no problem and the reason is really simplistic. See:

    http://www.ccsenet.org/journal/index.php/apr/article/view/33740

    Moreover, if one wants to solve 12 of the 18 free parameters of the standard model with many many more like in SUSY, well, I won’t buy this as a solution…

    Jacques

  65. […] are many more reasons why SUSY has been extensively studied as an extended theory of nature: see Starts With a Bang for an excellent summary of the hypothesis and its current state.  Unfortunate for SUSY, it does […]

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