Half Hour to Midnight

Matt Strassler posts here about a recent panel discussion of phenomenologists talking about the implications of the latest results from the LHC. You can listen to the thing for yourself, and see what Matt has to say at his blog, but here are some things that I noticed from watching the discussion:

  • I don’t recall string theory even getting mentioned once. The extent to which string theory is now agreed to be thoroughly irrelevant to LHC physics is kind of striking. The few people like Kane claiming otherwise are being ignored as an embarrassment. If evidence for SUSY or extra dimensions had shown up, this would be very, very different.
  • Arkani-Hamed is probably the dominant personality in this field, and as Matt mentions, he embodies the conventional wisdom of the subject, expressing it at length and with brio. Back in 2005 he was claiming we would know whether SUSY solves the hierarchy problem within a year of LHC turn-on. Somewhat more than a year after LHC turn-on, in February 2011, he was saying that we’d have to wait until 2020. Now he’s putting it differently: it’s the “eleven and a halfth hour” for the idea of SUSY solving the hierarchy problem.

    The only remaining hope for this is that there’s a light stop, which has so far escaped detection, and gluinos just above the current bounds. He sounds willing to bet against this, and is arguing that the idea may soon be toast, to be finally put to bed as results from better stop searches come in over the next few months. If there’s no sign of SUSY in the 2012 data set, it sounds like he’s willing to concede that SUSY can’t be what stabilized the weak scale.

  • On the other hand, he argues that a 125 GeV mass for the Higgs is evidence for SUSY. Here the argument is that such a low-mass Higgs must be an elementary scalar, not the sort of thing you get in technicolor or extra-dimensional models. “SUSY” is here equated with the SM, without comment. I’m not sure what the reason for this is other than the sociological reason that it’s the dominant remaining paradigm for BSM physics, I don’t see a positive scientific argument.

    The 125 GeV value is also described as uncomfortably inconclusive for the idea of SUSY explaining the hierarchy. It’s somewhat too high for this, but not so high as to make it impossible.

  • If the SM continues unvanquished at LHC energies, it sounds like conventional wisdom will move to “it still has to be SUSY, even though our main motivation for SUSY is gone, since we don’t have any better ideas.” Best guess for the SUSY breaking scale will move up to be just high enough to be unobservable at the LHC.
  • Clearly a lot of theorists are looking at the failure of the last quarter century of BSM ideas and trying to figure out what else they can work on. The idea of “back to working on QCD” was repeatedly mentioned. Arkani-Hamed has over the past few years dropped BSM work and moved to a radical speculative program about new ideas for QFT based on a different point of view about amplitudes. One of the speakers jokingly accused him of becoming a mathematician. Maybe that’s where things are going…
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51 Responses to Half Hour to Midnight

  1. Interested Observer says:

    There are still several SUSY scenarios that have not been explored at the LHC. These include violations of R-parity, spectra where the NLSP decays predominantly to the top quark, degradation of the “missing energy” signals through longer cascades etc. These require more data and effort before anything conclusive can be said about them.

    Of course, these models are not the “simplest” avatars of SUSY – but I doubt anyone would write down the standard model with its hideous yukawa structure if they were only motivated by “beauty” and unknown “top-down” philosophy. BSM physics may well exhibit similar complexity and if so, it would require effort to extract it from the dirty hadron environment.

    The important thing is that the LHC, as a machine, is performing very well and with time and effort, it should be able to probe several of these scenarios. And if anything, the first year of the LHC is a stern reminder of the importance of experiments in physics. For much of the past 30 years, we have unfortunately spent way too much time pursuing ideas solely on the basis of mathematical beauty and consistency. The LHC tells us that this armchair philosophy has not been useful in guiding us to describe physics at 1 TeV, a paltry order of magnitude above the 100 GeV scale explored at LEP. And yet, there are those who insist on extending these philosophies all the way to physics at the Planck scale, without the guidance of experiment. God be with them.

  2. Peter Woit says:

    Interested Observer,

    Fine to pursue searches for things like R-parity violating SUSY, as long as one acknowledges there’s no good motivation for such things (such models are hideously ugly and explain nothing), and this doesn’t interfere with actually important and well-motivated searches. I didn’t mention the obvious point repeatedly made by everyone on the panel: anything at all about the Higgs and its decays, as well as anything probing electroweak symmetry breaking in new ways, is incredibly important and should be the highest priority.

    At this point, I fear the best argument for obscure SUSY searches is just that no one has better ideas about where to look for something unexpected. If there are such ideas out there, I hope they’re not languishing because of higher priority being given to SUSY searches.

  3. Interested Observer says:

    I am not sure what you mean by stating that R-parity violation is “hideously ugly” or that “it explains nothing”. R-parity itself isnt particularly natural – it was imposed as a way to protect the proton. At low energies, this is guaranteed as long as either baryon number or lepton number is conserved. There are very reasonable, straightforward ways of breaking lepton number at low energies. Breaking baryon number is harder, but again, not impossible.

    Indeed, R-parity preserving models have the virtue of stable dark matter candidates etc. But, it may well be that dark matter has nothing to do with the hierarchy problem (could easily be axions), in which case R breaking models would be natural and dedicated searches should be done in their aid.

    I am not particularly trying to defend R-parity breaking, but I just want to reiterate that it is now time for people to do the broadest possible searches since the governing theology of the past 30 years ie: the package of the MSSM + dark matter is very much at odds with experiment.

  4. Garbage says:

    CMB fluctuations were detected five seconds before midnight. There also a theory: inflation, was proposed to solve a ‘naturalness’ problem (e.g. flatness), and we’re waiting for PLANCK to give us some hints to nail it. Perhaps the LHC is like COBE, if the branching ratios stay (believable) away from SM; and like Nima says, we’ll need ILC, etc (WMAP…PLANCK) to be able to probe SUSY at the high scale.

    SUSY at the 100TeV scale won’t be fully natural, neither is inflation for that matter (ask Steinhardt). But truly is the *only game (left) in town*. Yes, this smells like string theory as a theory of QG. Perhaps the universe is fine tuned and that’s about it (read CC), or perhaps there’s some aspects of tuning we yet don’t understand.

    I’m not sure I buy Nima’s argument that m_H ~ m_Z = SUSY-like. The Higgs was designed to break EW symmetry. We knew G_F, hence the vev. One could have naively guessed: m^2_H ~ 1/G_F, which is obviously too high, so toss in some weak-coupling constant (\lambda) and voila, 100-ish GeV. (In fact, that’s a very educated guess, considering e~0.3) It is true SUSY gives us a ‘natural’ mechanism for m_H at~ m_Z (or smaller, ahem…) but the Higgs still is where we expected it to be, SUSY hasn’t ‘predicted’ anything here so far… All we hope for now is a confirmation the Higgs was found and significant departures from SM-like decay rates. Even a 300-ish GeV 2HDM could do at this point, so there’s perhaps *new physics* to be found…

    By the way, I’m not sure what you think of Matt S. attitude: “let’s try everything”. That’s not how physics works…

  5. Peter Woit says:

    Garbage,

    I just don’t see any serious motivation at all for 100 TeV scale SUSY, from string theory or anything else, other than that a large group of theorists have careers invested in SUSY phenomenology and don’t want to acknowledge that this hasn’t worked out.

    Matt S. seems to me obsessed with making sure to be extremely cautious and not acknowledge what has almost surely happened until it is 99.999% all locked up. For instance, he was paying attention to the OPERA FTL neutrinos long after it was clear there was no point to this. I suspect he’ll also be working hard on obscure SUSY searches long after this is also a waste of time. The real question is whether there’s something more promising the LHC experiments could be looking for. To my mind, the sooner phenomenologists admit that SUSY is a failed idea and devote their energies to other things, the better.

  6. john McAllison says:

    Peter, great that you’ve posted the link to the audio talk of Arkani-Hamed in 2005, but I’m sure there’s an important public talk he gave before 2010 on the expected LHC milestones. It’s fascinating because I’m sure he talks about susy being discovered within two years – maybe even before the Higgs. I’d love to be able to see it again.

  7. Peter Woit says:

    John McAllison,

    I’m not sure what talk you’re referring to, Arkani-Hamed is a favorite invited speaker for talks of this sort, so there have been lots of them, although most not available on-line. The idea that SUSY would be an early discovery, the Higgs much harder and later was always conventional wisdom. The simple reason is that SUSY was supposed to be visible via strongly-interacting partners (gluinos and squarks), which would be copiously produced, even at low luminosities, whereas Higgs production is a weak process. This was borne out, as even the earliest LHC results at low luminosity provided impressive limits on SUSY, nothing about the Higgs until later.

  8. MathPhys says:

    Well, look on the bright side. We surely have quite a bit to learn over the next 5 years. Exciting times in high energy physics.

  9. Kevin Lahey says:

    I just wanted to say I appreciate the summation and straight talk about latest results from the LHC data. Keep up the good work.

  10. Cesar Uliana says:

    Peter,

    Could you comment on why Peskin said that the Higgs implies BSM? The talk seemed to me that if the Higgs is at 125 GeV then SUSY is not much of a help.

    On a side note, could you explain why the Physical Review Letters has published an article saying that Lorentz force is wrong? It’s on the arxiv http://arxiv.org/abs/1205.0096 as well as the PRl page. Really amusing.

    Thank you

  11. Peter Woit says:

    Cesar,

    I don’t remember exactly what Peskin said, and I don’t know what he had in mind. Not having a Higgs would definitely be BSM physics, having one is just the SM (if it behaves like an SM Higgs should, that’s what everyone wants to find out from the LHC).

    I heard about the Lorentz force controversy, but I confess to a lack of either expertise or interest in the subject. There’s a nice story about it here

    http://www.sciencemag.org/content/336/6080/404.full

    but you need another site for an informed discussion.

  12. neo says:

    “MathPhys says:
    May 7, 2012 at 10:56 am

    Well, look on the bright side. We surely have quite a bit to learn over the next 5 years. Exciting times in high energy physics.”

    What that be true if the SM holds with no deviations?

  13. Peter Woit says:

    neo,

    Even in the nightmare scenario of no SM deviations, we’ll learn something. I think that one thing the field is already starting to learn is that the whole SUSY scenario that so much effort and attention went into was a mistake. The LHC’s big accomplishments may be confirming the Higgs sector and shooting down some bad ideas which have dominated the subject for too long. Of course, will be even better if it provides hints for where to look for better ideas.

  14. MathPhys says:

    If SM holds with no corrections, then we’ll learn that ideas such as naturalness, and our views about radiative corrections, what is large and what is small in perturbative renormalization theory, etc, are too simple minded.

    On the other hand, rejecting supersymmetry altogether is too radical to contemplate at this stage (too many papers on the subject, too many good names on the line), and anyone who advocates that viewpoint puts himself in the same position as those who advocate supersymmetry since the late 1970’s.

  15. God says:

    The Standard Model works and is fantastic. Its *main* problem is the hierarchy problem (followed by no dark matter, no baryogenesis, inflaton, no grand unification, or including gravity), so if nothing is found at LHC, theorists will have to scratch their heads as to what is going on to keep the EW scale so low. If no low energy SUSY is found (and I agree with Peter, its just about dead already), then I think we have 2 possibilities:
    i) anthropics to explain the smallness of EW scale
    ii) dynamical explanation that no-one has come up with after all these decades of trying
    I think its a little too easy for Peter to just say that theorists should try other ideas…they do all the time…only SUSY seems to fit together nicely. But nature doesn’t care about that. thank goodness experiment is pointing the way forward by killing it. so maybe we are left with i)…yikes…

  16. HypeWatch says:

    Oh Lord: hunt is on for 5 God particles
    Jonathan Leake, Science Editor
    The Sunday Times, 6 May 2012

    Rolf-Dieter Heuer, director of the laboratory, has admitted there could be a family of Higgs particles and this could keep his team in work for 20 more years: “There could actually be a number of Higgs particles. In fact there could be up to five.”

    After smashing 640 trillion protons together, the Large Hadron Collider, Cern’s giant particle accelerator, has generated 80-100 possible Higgs bosons. But the number of candidates is slightly more than predicted.

    “One possible reason is that there is more than one Higgs,” said Heuer. “And if there is more than one, then theory suggests there could be up to five.”

    This hypothesis is known as “supersymmetry”, which predicts each known sub-atomic particle could be partnered by another “superparticle”, although these remain undetected.

    Heuer remains confident that Cern scientists will soon confirm at least one Higgs. “We will know if the Higgs exists at all by the end of this year. That I can pledge,” he said.

  17. Peter Woit says:

    God,

    I’m still not convinced that the big problem of the SM is “what keeps the electroweak scale so low?”. Low compared to what? It’s actually a high-moderate scale compared to any energy scale we actually understand. Without seeing a proton decay, there’s no evidence for GUTs and a high GUT scale, and about quantum gravity we know even less.

    The Higgs field and the Higgs mechanism for EW symmetry breaking is the most dubious part of the standard model, crying for someone to find a better alternative (and yes, I know people have been trying, hard, for a long time..). But I’m not convinced that the supposed hierarchy problem is the key to anything. It’s going to get used by anthropicists as an argument for giving up, but it’s not a good one.

  18. Peter Woit says:

    Hypewatch,

    Thanks. But why stop at 5? Surely one can find SUSY models consistent with experiment with more than 5 Higgs particles…

  19. God says:

    I don’t get your answer. I can only take from your answer that you don’t really understand what the problem is; the problem is that the EW scale is sensitive to quadratically divergent corrections. So the SM taken at face value, assumed to be valid up to arbitrarily high energies requires infinite fine tuning. If it is taken to be valid up to, say, the Planck scale, then it has 1 part in 10^30 fine tuning, etc. So it indicates that something should intervene to keep the scale low.
    Your point that we don’t know much about the GUT or quantum gravity scale doesn’t alleviate the problem at all. If the GUT scale is 10^15 GeV or so, as is usually assumed, then we have a 1 part in 10^26 fine tuning if the SM is valid up to this scale. If you are alternatively suggesting that we know so little about GUT physics that the “true” GUT scale might turn out to be a TeV or so, well great; so that is the wild new physics that we are hunting for! Either way, the existence of the hierarchy problem tells us that crazy fine tuning is required or new dynamics is present. What about this do you not understand?

  20. Peter Woit says:

    God,

    My point is that we not only don’t know what the right GUT is, we don’t even know if there is a GUT or a GUT scale. We really know nothing much for scales above 1 TeV or so. Describing the hierarchy problem as not knowing how to keep the EW scale very small compared to the GUT or Planck scale seems to me a robust way of characterizing the hierarchy problem, but it requires a high GUT or Planck scale, and these things are huge mysteries in themselves.

    The quadratic divergence problem comes from applying perturbation theory and a momentum cutoff to the dynamics of the Higgs field at energy scales one knows nothing about. This kind of behavior of elementary scalar fields does look like an indication of something pathological about them at short distances, but there are other reasons anyway to be unhappy with elementary scalars.

    Maybe one way to explain my point of view is that I see the bad high energy behavior and sensitivity to the cutoff of elementary scalar fields as maybe part of the problem, but that’s not the same as “why is the EW scale so low?” unless you postulate some unknown BSM physics at a scale that acts as an effective momentum cutoff for the perturbative Higgs calculations. We’re just barely starting to be able to observe the effects of tree-level physical Higgs field processes. Is there really any indication that Higgs loop processes are there and behaving like elementary scalars? I’m no expert on higher-order SM calculations, and I’d be curious to hear from someone who is, but I’d assume that if these calculations were significantly sensitive to physical Higgs loops, we’d have had a much better fix on the Higgs mass than we did pre-LHC.

  21. Wilson's ghost says:

    I think a lot of the discussion has to come down to understanding renormalization. The SM is renormalizable in the “old” sense and in principle none of this matters as long as the Higgs mass resides within a certain window. On the other hand from the Wilsonian point of view, clearly a Higgs behaves differently. Peter, I’m not clear as to what you mean about higher-order SM calculations. The problem arises from the mass renormalization of the Higgs, not the effect of the Higgs entering into other calculations (e.g. unitarity of WW scattering in the SM). One last thing to point out is there isn’t any vodoo associated with the modern view of wilsonian renormalization and effective field theories, we use it all the time often to describe pretty difficult situations in QCD that are naively strongly coupled.

    Now if there were no other scales beyond the TeV scale, we could just throw our hands up and say sure, there is no problem with fine tuning. Ironically this is akin to the original prescription for large extra dimensions which bring the Planck scale down to the TeV scale. However, this of course has consequences experimentally which we have seen none of. To do so without a model (more along the lines of what Petr is suggesting) means we should have an infinite set of higher dimension operators suppressed by the TeV scale. Of course we’ve searched for these things and found nothing of the kind. Now of course one can claim there is no higher scale, but the point is then there are a whole host of OTHER problems that become more pressing. This is also similar to the field theoretic understanding of the fact that if the Higgs weren’t elementary there should be a whole host of higher dimensional operators at the TeV scale associated with strong dynamics that we don’t see. This really isn’t a matter of understanding perturbation theory, it’s understanding if there is some pink unicorn theory that solves all the outstanding problems of the SM and leaves no traces elsewhere. There are certainly methods to understanding the implications of strong dynamics, and they all tell us we should be seeing something more if it’s not an elementary Higgs. Additionally there definitely are much higher scales associated with the problems in the SM (listed by God) otherwise we would have seen experimental effects associated with flavor and CP violation popping up all over the place.

  22. Ravi K says:

    Hi Peter,

    Considering that neutrino masses define a new mass scale we naturally now have high mass scales such as M_W (M_W/m_nu) in the theory. I don’t think the argument that we don’t know whether large mass scales exist or not in the quantum field theory can be made.

    However whether the hierarchy problem needs a solution or not may still be a relevant issue, even if there are large mass scales. If nothing new other than the std. model Higgs is discovered at LHC, I guess we would have to conclude that it does not need one.

  23. MathPhys says:

    Peter Woit writes “The quadratic divergence problem comes from applying perturbation theory and a momentum cutoff to the dynamics of the Higgs field at energy scales one knows nothing about. This kind of behavior of elementary scalar fields does look like an indication of something pathological about them at short distances.”

    Or maybe there is something pathological about using a perturbative expansion where terms diverge one by one, we know that there are no divergences (the electron has finite mass and charge) so we subtract the divergences, then we complain that the subtracted terms must be finely tuned.

    Maybe it is this way of doing things that is pathological in the presence of elementary scalars.

  24. Peter Woit says:

    Ravi K,

    The problem of neutrino masses you mention is “why is the electroweak scale so large?, a different one (if you get neutrino masses by a see-saw mechanism you do get a new large scale, but there’s no evidence that you need to get them that way). I agree that the problem of fermion masses, with their widely different scales, is about the biggest mystery around. By the way, there’s something about this that has always bothered me that maybe someone can explain: supposedly the Yukawa coupling to the top is very close to 1 (an accident or a hint?). Doesn’t this ruin one’s ability to compute Higgs physics in perturbation theory (since the coupling is not small)?.

  25. Peter Woit says:

    Wilson’s ghost,

    My point was just that the significance of a one-loop perturbative mass renormalization calculation by itself is unclear: is this just a technical problem with perturbation theory? I’d be more inclined to take it seriously if we were in the situation of QED, where you can physically measure effects (g-2, for instance) that show that loop calculations are correctly giving you something physically observable.

    I agree that getting the Higgs out of unknown strong dynamics at the TeV scale introduces its own problems, and certainly don’t claim to have any good idea about how to resolve the problems introduced by the Higgs. It just seems like a good idea though to stay clear on exactly what the problems are and whether one comes from something you have solid knowledge of, or from some speculative framework that you understand even less (e.g. I’m not going to worry so much that the properties of the inflaton cause this problem with the Higgs).

  26. Ravi K says:

    Peter,

    The neutrino masses break B-L symmetry and there is a fundamental new mass scale associated with this breaking — I think whether it is larger or smaller than M_W is immaterial as the hierarchy argument can always be made for the Higgs sector of the smallest scale.

    If the B-L breaking scale is around the weak scale then it would have observable consequences at the LHC….for example a B-L breaking Higgs.

  27. YBM says:

    Some (unrelated to the article) news on the Bodanov Affair:

    Researchers and the threat Bogdanov

    The french scientific community reacted strongly:

    Affaire Bogdanov : lettre ouverte de 170 scientifiques

    By the way, as you know, their main “protection” in the political world has just lost his job.

  28. Ravi K says:

    Is there a renormalizable theory for the observed neutrino masses without having either a high mass scale (like see-saw) or a new light Higgs particle?

  29. Peter Woit says:

    Ravi K.,

    I don’t know, maybe someone more expert on neutrino masses can comment. But if you do this with a right-handed neutrino and another Higgs field, I don’t see why the new Higgs can’t be at the electroweak scale. Yes, you wouldn’t know why Yukawa couplings were so small, but we already have that problem in the rest of the SM.

    I guess that to me it’s the Yukawas that are the huge mystery here, it’s a huge array of numbers we understand not at all, even though we can measure them precisely.

  30. Ravi K says:

    The new Higgs can be at the electroweak scale — thats what I meant by the light Higgs — EW or lighter — but then it would have observable consequences at LHC and at some point will be ruled out.

    The Yukawas hierarchy can be at least understood as being due to chiral symmetries that get restored as the fermion masses go to zero. For example if the electron mass is zero then there is an additional chiral symmetry that will explain this.

    This is the ‘tHooft criterion for naturalness (electron, up and down quark masses satisfy it) : At any energy scale mu, a physical parameter or set of physical parameters alphai(mu) is allowed to be very small only if the replacement alphai(mu)=0 would increase the symmetry of the system.

  31. God says:

    Peter you still seem confused about basic QFT of scalars. Scalars suffer quadratic corrections to their mass, unless protected by a symmetry. Hence the SM, which does not carry any such symmetry, by itself has infinite fine-tuning. One either accepts this, OR there must be new physics at some scale of the order of a TeV or so. That’s what the realization that scalars have quadratic divergences leads to. Its a profound conclusion, and by itself has nothing to do with GUTs, etc. Hence, we should see all sorts of new physics at < 1 TeV, or there is fine tuning. What is it you don't get?

  32. Peter Woit says:

    God,
    You seem to just ignore everything I write, in favor of the idea that I must not understand the conventional calculation and the conventional arguments about what it means. For your benefit:

    I DO KNOW HOW TO COMPUTE ONE-LOOP FEYNMAN DIAGRAMS AND THAT YOU GET A CONTRIBUTION TO THE HIGGS MASS QUADRATICALLY DIVERGENT IN THE MOMENTUM CUT-OFF.

    OK? The question is what to make of this. Is it (and the necessity of “fine-tuning”) just an artifact of perturbation theory? This kind of sensitivity to short distances is one of several legitimate reasons to be suspicious that something funny we don’t understand is going on with the idea of the Higgs as an elementary scalar. We’re just starting to probe the behavior of the physical Higgs field at its lowest excitation energy. I don’t see that it’s useful to formulate the main problem of the Higgs as “fine-tuning is necessary to keep the Higgs mass small compared to some speculative physics at some high energy scale we know nothing about”. That certainly hasn’t been a fruitful avenue to pursue so far.

  33. JR says:

    Not an expert but: If you do the one loop calculation with dimensional regularization you get a 1/epsilon pole instead of the quadratic divergence. Is that not a hint that the fine tuning argument is a red herring?

  34. Florian says:

    Hello,

    tomorrow’s Sueddeutsche Zeitung, a German, high quality newspaper based in Munich is running an interview with Lisa Randall in its Wednesday issue. The occasion is some book of hers (knockin on heaven’s door) appearing in German. I’d like to share the highlights of the interview. Since I am translating back something somebody has translated from English this will probably not be literal. Here goes.
    […]
    SZ: You are trying to find pictures for these invisible worlds and you have developed a theory after which the universe has 4 space dimensions. Accordingly there could be parallel universes, which are very close to us.
    LR: They are probably only 10-31 cm away. But these extra dimensions cannot be observed directly, because they are very small and rolled up.[…]
    […]
    SZ: You attach a great importance to the fact, that your theories can be experimentally tested. Your calculations may be tested at the LHC. Can we expect new discoveries?
    LR: After initial difficulties the LHC works now incredibly well, so I hope so.
    SZ: I would have expected a clear “Yes” here.
    LR: The reason why I am not sure is connected to the energies the LHC is able to reach. They might not be high enough to find the particles we are looking for. The once planned American supercollider (SSC) would have reached energies 3 times as high as the LHC, that would have made me more confident. At least we are now seeing clues of the Higgs Boson. But there are a few fascinating theories, like extra-dimensions or Super-Symmetry, in which heavy particles play a role. We could be lucky and see these particles at the LHC. But it could also be that we nearly miss these energies, which can give us the right answers.
    […]
    There is other stuff, which is amusing, but I’m too lazy to translate that. The 10-31cm and the almost caught particles are the best part anyway. It would be amusing, if it wasn’t so sad. Sorry for being slightly off-topic, Peter.

  35. JustDisWonce says:

    @God,

    you are parroting the standard story used to sell SUSY for decades. That this story is so ingrained in the community may reflect great marketing more than great physics. While this story may turn out to be correct, the data thus far suggests otherwise. If nothing is found to stabilize the weak scale, “the community” is presumably thinking incorrectly about the matter. Time will tell. (These last statements are not controversial.)

    From your comments, my guess is that you have not studied the corrections to the Higgs mass in detail (as I find with a number of my “expert” colleagues), as the matter is not as trivial as you imply. Study and figure out your own answers to questions like the following: How does this “problem” manifest itself in different regularization schemes? What is the physical meaning/origin of this difference (if any)? Which regularization scheme is “better” — does it even matter? Why are some schemes better in eg SUSY models; ie why do we choose regularization schemes in SUSY models that preserve the SUSY (an obvious one)? Does the answer to this question have any implications for the regularization of the SM (or implementation thereof)? What about if you send the bare Higgs mass to zero — does the way in which scales manifest via the trace anomaly alter your answer (see Bardeen’s work)? Does the answer to these questions depend on whether there is a UV scale describing QFT-able physics like M_GUT? If there is no M_GUT, does the answer depend on the nature of quantum gravity (this one is harder)?

    If you can answer these (except the last one, of course), you will understand what Peter is saying —- if not it would take more time to explain than any self-respecting person would have to spare.

    An aside: if more people spent time pursuing original research directions in the ’90s, rather than telling everyone else that SUSY was the only solution to the hierarchy problem, there is no apriori reason why things like ADD, RS and Little Higgs could not have been discovered earlier (no offense meant to the very insightful folks who eventually did make these discoveries). These statements alone are a good reason to be wary of anyone who tells you string theory/SUSY is the only hope, rather than encouraging diverse research programs to explore as many possibilities as are conceivable.

    @Peter,

    I congratulate your efforts and applaud your patience in responding to these same comments over and over again. Though no doubt tiresome, it is a valuable service.

    @Ravi

    There are a number of eg radiative models that generate nu mass without invoking high (beyond ~ TeV) scales; these are renormalizable and easily accommodate the data. The problem with neutrino mass is not that its hard to explain (nor that the existence of the scale m_nu implies a hierarchy problem), rather it’s just too easy to write a renormalizable theory that explains the data, is completely natural, and has new physics at (almost) any scale you care to mention. This is what makes nu theory somewhat boring (along the lines of Jester’s recent post); only experiment can shed light on the matter, but the scales may or may not be accessible and the couplings may or may not be large enough to allow detection. Also note that nonzero m_nu does not imply that B-L is broken; neutrinos can just as easily be Dirac particles and nu mass will be competely natural.

    If one adopts the view that the SM Higgs mass is tuned, then this, at least, is a much more difficult problem to solve (thus the high number of original nu-mass-models compared to the number of original solutions to the hierarchy problem).

  36. pah says:

    I’d also be interested to hear an answer to JR’s question above.

  37. Anonyrat says:

    pah, JR,

    My memory is failing – I was sure I had a copy of this 1975 book: “Dimensional Regularization and the Renormalization of Quantum Field Theory”, John C. Collins, but I can’t find it. I’m about just as sure that in this book J.C. Collins worked out an example of a toy model with two scalars, one light and one heavy, and showed that even with dimensional regulation, the light mass was inexorably drawn to the heavy scale unless there was fine-tuning. But my memory is suspect.

  38. Anonyrat says:

    I’d appreciate being reassured that my memory is fine. 🙂 Anyway, if there is a GUT, then we have a hierarchy problem.

    http://arxiv.org/pdf/0708.3550v1.pdf

    “In fact, the structure of divergences does depend on
    the regularisation scheme. One can use also the scale- independent regularisation, such as the dimensional reg- ularisation of ’t Hooft and Veltman [48]. In this scheme the renormalization of parameters is the multiplicative one and thus there is no difference in removing the divergences from dimensionless parameters such as gauge coupling or dimensionfull parameters such as the mass of the Higgs boson. However, inspite of these specific features of the dimensional regularisation the conclusion about fine tunings remains intact [49]: even in this scheme to have a field theory GUT with two or more well separated scales one has to tune a number (varying from 1 in SUSY GUTs to 14 in non-SUSY GUTs) of terms to achieve the hierarchy of masses.”

    Reference 49 is:
    [49] S. Weinberg, Phys. Lett. B 91 (1980) 51.

  39. God says:

    @JusDisWonce,
    I am not parroting anything about SUSY, etc. Personally, I doubt low energy SUSY is right – i said that in my first post, see above, so your discussion is off target.

    @Peter,
    Sorry, but what you are saying doesn’t make sense. The basic principles of effective field theory guarantees that the SM extrapolated to high energies is highly fine-tuned. If you are disputing this, you are disputing the core principles of EFT. If so, then please state so. You will be wrong, but you should at least state so clearly, so I understand the claim you are making. The alternative to this fine tuning is some form of new physics; I do not know what form the new physics will take. These arguments are completely general, they have nothing to do with GUT theories, etc.

  40. MathPhys says:

    Anonyrat,

    Your memory is okay.

    In fact, the first paper that gives an explicit computation in which the ‘technical fune tuning problem’ shows up is by E Gildner (a PhD student of S Coleman) from the late 70’s, and there he uses dimensional regularization.

  41. MathPhys says:

    On a different matter, can an expert confirm or deny that one can compute scattering amplitudes, even for massive scalars, and that the results are finite and no divergences show up anywhere in the intermediate steps?

  42. Garbage says:

    “I think that one thing the field is already starting to learn is that the whole SUSY scenario that so much effort and attention went into was a mistake.”

    I’m not a big fun of susy at the EW scale myself either; I do believe though susy is too pretty for nature to pass on it at the GUT scale. However, susy at 100TeV is still partially motivated. Nature may have a split spectrum whether we like it or not. If the departures form the SM decay rates withstand further scrutiny, then high-scale susy will be by far one of the most natural options to look for an explanation. Now, if we find *just* the Higgs with 1-2 sigma-ish deviations from SM here and there, then is another story… Nima will tell you we need to measure the electron’s dipole moment, gotta get down to 10^{-31} (current bounds at 10^{-28}). The cool thing is that there’s still a lot of physics to be done and understand before we accept the universe is fine tuned for good…. (we have almost done it with lambda…)

  43. SpearMarktheSecond says:

    How about mentioning the theorists who long ago (even prior to, say, 1997) became disenchanted with SUSY at accessible energies, and sort of moved on? I can think of two easily. It would kind of compensate the negative undertones.

    One of the two is Tini Veltman…. although the quote is from 2004, I can remember him saying this stuff through the 1990’s….

    http://www.timeshighereducation.co.uk/story.asp?storyCode=187373&sectioncode=1

    “Anyone who thinks that string theory has, in the meantime, shown the way that particle physics is going gets short shrift from Veltman. Supersymmetry and string theory are “figments of the theoretical mind”, he writes.”

  44. MathPhys says:

    SpearMarktheSecond,

    Veltman says these things, and in stronger terms, since the early 80’s.

  45. Anonyrat says:

    MathPhys,
    What were Veltman’s stated reasons in the early 80s for giving short shrift to supersymmetry?
    Thanks in advance!

  46. Peter Woit says:

    Veltman was far from the only one to be skeptical about supersymmetry. Among the other Nobelists I can think of who never showed much interest would be Glashow and ‘t Hooft. Actually I suspect that faith in SUSY has always been a minority viewpoint among theorists (although the minority has been much louder than the majority). For some evidence about this, see how people lined up back in 2000:

    http://www.staff.science.uu.nl/~hooft101/susy_wager_2000.gif

  47. MathPhys says:

    Anonyrat,

    I didn’t hear him give any reasons. I only heard him say

    “Gordy, if they discover supersymmetry, I’ll eat my hat”,

    then he mimicked eating his hat.

  48. MathPhys says:

    That’s a significant historical document you’ve linked to above, Peter. I haven’t seen that before.

  49. Ravi K says:

    @JustDisWonce

    I will try and give a more general argument than what I gave before. For masses of charged leptons such as the electron you just need the Yukawa couplings and no new term in the Lagrangian of mass dimensions (need only the usual std model Higgs mass term). However for the neutrino mass you can’t get from Yukawa terms alone and the std model Higgs — you need to introduce some other term with mass dimensions no matter what the model. If this mass term is much more than the electro-weak scale then even in Peter’s sense there would be a hierarchy problem as his artifact argument crucially depends on there being only one mass scale in the QFT. On the other hand if it is at the weak or TeV scale or lower then it would inevitably lead to new physics that the LHC or a future generation of colliders should see. If there is no new physics and only a std model Higgs then you will essentially end up with two different mass scales in the QFT — one to explain the neutrino masses and the other the weak scale. Even as theories like SUSY getting constrained so are all other new physics theories at or near the weak/TeV scale. If nothing new is found then fine-tuning must exist even in the sense Peter is talking about where you regard the cut-off as an artifact.

  50. Trulo says:

    Peter, the document you link to says that “The party of winners organizes a meeting of all involved in this wager not later than in June 2011” in which the cognac bought by the losers of the bet will be drank. I’m curious to know if that meeting has already taken place, or if it has at least been announced.

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