The announcement at CERN tomorrow of a likely-looking signal for a 125 GeV mass Standard Model Higgs will probably unleash a flood of hype from theorists claiming this as evidence for their favorite Beyond the Standard Model scenario. One obvious problem with any such claim is that the CERN results correspond well so far to the Standard Model with no additions whatsoever, so spinning them as providing support for things like supersymmetry and string theory will require some work.
For the last decade we have known that the Higgs mass is above 114 GeV (from LEP) and unlikely to be very much higher than that (from precision electroweak results). This summer’s LHC results disfavored masses above about 130 GeV, so for the last few months we’ve known that if the Standard Model Higgs is there, it should be between 114 and about 130 GeV. For a couple weeks news has been circulating widely from ATLAS and CMS that they are both seeing something around 125 GeV.
First out of the gate in the hype derby is Gordy Kane, who is quoted by Davide Castelvecchi at Scientific American claiming that string theory predicts the Higgs mass to be between 122 and 129 GeV:
“If it’s in that range it’s an incredible success for connecting string theory to the real world,” Kane says. He says he is confident that the upcoming LHC announcements, if they pan out as predicted, will constitute evidence for string theory. “I don’t think my wife will let us bet our house, but I’ll come close,” he says.
It’s unclear exactly what he’s willing to bet the house on. If it’s just that the Higgs is in that range, this might have something to do with the plots from the experiments widely circulating privately the last few days. In a remarkable coincidence, after more than 25 years of unsuccessfully trying to extract a definite experimental prediction from string theory, Kane and collaborators were able to achieve the holy grail of the subject (a prediction of the one unknown parameter in the SM, the Higgs mass) just a week before the CERN announcement. They submitted their paper to the arXiv the evening of Monday December 5, a few days after rumors of a 125 GeV Higgs were posted on blogs Friday December 2.
The paper deals with a “prediction” you get based on a host of assumptions about which particular class of string theory compactifications to look at. The main result is that in this particular class of models, you can relate the Higgs mass to the parameter tan(β) that occurs in SUSY extensions of the SM. As you increase tan(β) from around 2, the Higgs mass lies in a band, increasing from 105 GeV and a maximum of about 129 GeV:
We will demonstrate that, with some broad and mild assumptions motivated by cosmological constraints, generic compactified string/M -theories with stabilized moduli and low-scale supersymmetry imply a Standard Model-like single Higgs boson with a mass 105 GeV < M_h < 129 GeV if the matter and gauge spectrum surviving below the compactification scale is that of the MSSM, as seen from Figure 1. For an extended gauge and/or matter spectrum, there can be additional contributions to M_h.
This conclusion and Figure 1 correspond closely to what is in the slides of Kane’s talk at String Phenomenology 2011 this past August. The plot of Higgs masses as a function of tan(β) is there, giving a range of 108 GeV to 127 GeV. There is an intriguing comment on the conclusion slide:
Single light Higgs boson, mass about 127 GeV unless gauge group extended.
I can’t tell where the number 127 came from. Since 127 GeV is the top limit in the figure, and the wording “unless gauge group extended” is used, one guess would be that Kane meant that 127 GeV was the upper bound on the Higgs mass in this class of models.
There’s nothing in Kane’s August talk about a 122-129 GeV range for the Higgs mass, but in the December 5 paper it appears explicitly three times:
When the matter and gauge content below the compactification scale is that of the MSSM, it is possible to make precise predictions. In this case, we predict that there will be a single Standard Model-like Higgs boson with a calculable mass 105 GeV < M_h < 129 GeV depending on tan β (the ratio of the Higgs vevs in the MSSM). For tan β > 7, the prediction is : 122 GeV < M_h < 129 GeV.
I don’t see where the tan β > 7 comes from, presumably it’s in one of their other papers.
Furthermore, in G2-MSSM models [1] we find that the range of possible Higgs masses is apparently much smaller, 122 GeV < M_h <129 GeV.
For instance, in G2-MSSM models arising from M theory, Witten’s solution to the doublet-triplet splitting problem [38] results in μ being suppressed by about an order of magnitude. Hence, in these vacua, the Higgs mass sits in the range 122 GeV < M_h < 129 GeV.
Kane has chosen Lubos Motl’s blog as the place to guest post and promote this string theory “prediction”, concluding there:
If generic compactified string theories with stabilized moduli correctly predict there is effectively a single Higgs boson and correctly predict its mass, it will be a huge success for the main directions of particle physics beyond the Standard Model, for supersymmetry and for string theory, both of which are crucial for the prediction. It will be a huge success for LHC and the accelerator physicists and experimenters who made the collider and the detectors and the analysis work. It will put us firmly on the path to understanding our own string vacuum, and toward the ultimate underlying theory. The value of the Higgs boson mass not only confirms the approach that predicts it, remarkably depending on its numerical value it may allow an approximate measurement of tan β, the μ parameter, the squark and gravitino masses, that the gauge group and matter content of the theory below the string scale is that of the MSSM, and that light (TeV scale) gluinos and dark matter are likely.
I don’t quite see how finding a SM Higgs at 125 GeV is going to give all these different numbers and pieces of information. Kane claims that these string theory predictions also predict gluinos visible at the LHC within months from now:
Then the gluino should be detected at LHC, and because of the heavy scalars the gluino decays are different from the ones usually discussed, being dominantly to third family quarks, top and bottom quarks. I won’t explain that here because of space and time; we can return to it as the gluinos are being detected in coming months. They have not yet been systematically searched for.
In addition, there’s a dark matter prediction that should be tested in “1-2 years”.
If I were Kane, I wouldn’t bet my house (or go to the press claiming the 125 GeV Higgs as a “huge success” for string theory) just yet. Assuming he’s right, within months the gluinos will be there, and his ticket to Stockholm will be assured.
Update: My prediction in the first paragraph is coming true faster than I thought. In tonight’s hep-ph listings one finds:
http://arxiv.org/abs/1112.2415 (m_H= 127 +/- 5 GeV)
http://arxiv.org/abs/1112.2462 (m_H < 128 GeV)
http://arxiv.org/abs/1112.2659 (m_H =126 +/- 3.5 GeV)
http://arxiv.org/abs/1112.2696 (m_H > 120 GeV)
There are going to be a lot of these…
Update: Over at a Nature live chat, Kane is giving the public some interesting explanations:
“for a higgs to be meaningful it must be part of a supersymmetric theory, so the superpartners should be found. The form it takes implies that gluinos should be found with masses around a TeV, maybe less, by summer, and decaying mainly into topquarks and bottom quarks.”
“Recently we have published string theory calculations that imply the higgs boson mass is 125 GeV so if it is there are strong implications for connecting string theory to the real world, and for what the higgs discovery implies. we did that before the data.”
“string theories are now well enough understood to predict higgs physics”
There will be another live chat involving Kane tomorrow, this one at Science magazine.
Update: Just took a look at the Science chat. Kane seems to have completely lost touch with reality, somehow deciding that the two experiments have reached the 5 sigma level needed to claim a discovery. As far as I know, he’s the only one in the world to think this.
Gordy Kane:
YES. an experimenter from one experiment can’t say that, but theorists see that two different experiments both saw a signal at about the same mass, and also saw additional channels, so it’s a discovery!…
Gordy Kane:
The 5 sigma is a criteria people have chosen. i think as soon as the data are combined from two detectors, which is entirely legitimate, then the signal will indeed be over 5 sigma.
The following claims make about the same amount of sense as the discovery one:
Comment From Tom
Does the existence of a 125 Gev Higgs give any support to supersymmetry?Gordy Kane:
Yes. first, for a long time it has been known that the lightest higgs boson of supersymmetry should be lighter than about 135 GeV (actually closer to 140 GeV but people make assumptions), so this is consistent. Then the supersymmetric string theories as i mentioned do predict the 125 number and it is a supersymmetric lightest higgs boson.
Update: The hype goes on, with a column today at Nature.
Well, Kane did at least make a definitive statement (even if in a blog post, not a journal paper) about BSM particles, viz. gluinos will be produced at LHC and discovered in a few months. (The timescale will of course depend on the LHC operating schedule, a few months could easily become more than a year.) But, anyway, you have your definitive string theory/MSSM prediction of BSM. Consider it a Christmas present from Kane to you.
glukanos,
From his comments at the blog, the problem isn’t not enough data, but the experiments not having done the right analyses (they were wasting their time looking for “unmotivated sugra”). He seems to think that they are now doing the right analyses, thus the “months” rather than “years” estimate. Presumably he’s hoping for a Christmas present…
Since I’ve looked into the G2-MSSM scenario, it is probably worth mentioning that after moduli stabilization and SUSY breaking, the G2-MSSM scenario of Kane et al contains only *four* GUT-scale input parameters so it will be relatively easy to rule it out.
I think it’s worth pointing out once again that the Standard Model with such a low-mass Higgs isn’t really stable. This implies new physics to provide the stabilization, and supersymmetry is the best motivated option for this new physics. Furthermore, the Higgs mass has an upper bound in the MSSM of around 130 GeV. So, it is likely that supersymmetry will eventually be observed at the LHC. Then, models such as Kane’s can then really be put to the test.
Also, in contrast to the flux compactifications such as the KKLT scenario where one has no good reason to expect low-scale SUSY and has to fine-tune the tree-level flux superpotential to 15 orders of magnitude to get TeV scale SUSY, the non-perturbative M-theory vacua that result in the G2-MSSM scenario generate low SUSY breaking scale dynamically via the mechanism of dimensional transmutation (strong gauge dynamics).
Eric, speaking of the SM being unstable, can you comment on this?
http://arxiv.org/pdf/1112.2150
emile, remarkable if true!
We must not trust the signal which amounts to the 2~3 sigma.
That signal may disappear in the next analyzing the remained data.
I don’t understand why CERN will announce as it is the real signal.
Why?
I doubt if we trust the result of experiment done in CERN.
We must not believe any result until that proves true
I am no fan of this site, but I will say two things:
A) Kane knows less string theory than an unborn baby (less, because he knows many things that are not demonstrably true).
B) String theory is in no state to predict the Higgs mass. This is simply impossible, at this time, given whats known about the theory.
Don’t take my word for it. If you’re anywhere near a top 10 physics department, ask your local string theorist. Other issues (AdS/QCD? AdS/CMT? The controversial “Landscape”?) will bring nuanced responses, with uncertainty from good theorists. Not one will say string theory can now, in any reasonable sense of the word, “predict” the Higgs mass. They may say “random particular model X has N light Higgses!”. This is very very different.
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It is very disconcerting to see certain regulars at this blog acting as if the forthcoming LHC data unquestionably heralds the advent of the putative Standard Model Higgs boson. It seems close to proseletizing in the eyes of one who has a more skeptical view of the heuristic foundations of particle physics.
This wishful thinking: seeing only the positive “hints”; ignoring the various contradictions and uncertainties; downplaying the very shaky “predictability” issues, etc., seems uncomfortably close to the behavior of string/brane theorists who you rail against?
Troubling contradiction? Or am I too much of scientific skeptic? Or perhaps just too dim to receive the wisdom accessible to the fully initiated and sufficiently refined?
Albert Z
from a layman… surely Kane is not ‘predicting’ M_h, but rather it sounds like using the phenomena to tune ST parameters, and show that MSSM is ‘capable’ of producing a credible explanation. It’s the gluino mass that’s the prediction here, and I’ll await that result with bated breath!
I’ll await the data with bated breath. Kane is making a strong argument for mandatory retirement with his statements.
What a curious state of affairs we have in physics, where a “3 sigma” detection significance is taken by physicists to mean not a 99.9% confidence that the Higgs has been found, but something far lower. There are amusing statements on many blogs along the lines of “there’s a 50% chance these 3-sigma results will hold up”. Do people really not trust the analysis and fear systematics of the data from these large collaborations? Why doesn’t 3-sigma mean 3-sigma?
I know HE astronomers that would be ecstatic about 3 sigma detections of pulsations or some such phenomena in their data.
In my experience, high energy astrophysicists are frequently ecstatic about their 3 sigma “discoveries”, some of which indeed last long enough to appear in Nature 🙂 I’m more amazed the LHC folks understand their systematics as well as they do, and I’ll forgive them a sigma one way or the other.
Z: It doesnt mean “there is a 99.9% chance this is the Higgs” it means “if this was just random data the chance against this being nothing 99.9%”.
Which sounds interesting until you think if you look at 1000 things you will have a 50% chance of getting a 3 sigma result. Im not sure how they take into account the look elsewhere effect with this analysis however.
There is no need to be impatient, if its real, its not going anywhere 🙂
String theory is really an amazing theory. It is capable of predicting the Higgs mass almost fours days after the result is publicly known, what a triumph.
Seriously, I wonder if Kane is being deliberately scientific dishonest with this Higgs story or just forgot what predictive and explanatory power of a theory is.
On the other hand if he keeps the some standards for the possible non-observation of gluinos in the next moths and announce he now thinks the whole string idea is likely wrong, this would make me satisfied.
I took careful note of Albert’s comments, and I’ve been paying attention to recent developments. Sorry, but it doesn’t feel as if it’s just the BSM guys unleashing a flood of hype here.
The rumor is that after re-calibrations the CMS and ATLAS peaks do not coincide
Breaking rumors,
oh no! That would be so bad for string theory, I hope you’re wrong.
The explanation is as follows.
In astrophysics, a 3 sigma result usually is vindicated by more data.
In particle physics, a 3 sigma event often-as-not “disappears”.
See the difference?
Albert Z
@younghun park:
I’ve actually had someone, on another site, tell me that “Well, yes. 3 sigma data has disappeared in further analysis, but never when there’s been a theory there to predict it”.
Being a layman at all this (I read physics for pleasure – you can back away slowly, I won’t be offended), I didn’t have a good citation to refute that at hand; the only thing I could think of (and haven’t used yet) was solar neutrinos, where there was 3+ sigma of evidence that “we’ve got something wrong here”, although that’s likely not the way to word it.
Any thoughts?
I fear that the overzealous will go out of their way and swamp all media communication to convince an ignorant public that the Higgs now provides a new reason why string theory deserves all the support it can get. You may have to write a sequel to “Not Even Wrong”.
Whatever someone thinks of Kane’s work, it is demonstrably not true that he adjusted his predictions in any significant way as a result of the links. Nice job muddying that up though.
Is it really so hard to identify the logic favoring a large tan-beta from his august presentation? Its because the gravitino mass naturally wants to be close to that of the lightest the moduli, which must be heavier than around 25 TeV due to the cosmological constraints. So the 127 GeV mass is favored because thats where it stabilizes for large tan-beta. So its a real prediction.
You didn’t mention the reasons that G2 models were well-motivated in the first place, which is that they can naturally generate an ~electroweak mass scale while stabilizing moduli.
But I understand theorists aren’t allowed to use any data or logic besides “string theory is true” according to the exchange we had over at cosmic variance a while ago.
Cliff,
I don’t see what you’re complaining about in what I wrote. I wrote that I didn’t understand exactly where the 127 came from. If you’re telling me that the prediction of these theories is large tan(beta), and that as a result the prediction Kane is making for the Higgs mass is 127 GeV, that’s fine, but it’s not what he’s saying in the paper. For the first calculation of the Higgs mass directly from string theory, solving the biggest problem of the subject, it would be a good idea if he explained more clearly what exactly he is doing.
As for the exchange at Cosmic Variance, I have no idea what you’re talking about. I don’t know who you are, or whether you’re talking about an exchange over there weeks, months, or many years ago.
@Cliff, actually, you have it kind of backwards with regard to the gravitino mass, the constraint on the gravitino mass M_{3/2} less than O(10-100) TeV in these vacua does not come from cosmology but instead it comes from setting the tree-level vacuum energy to be small. Then, when they compute the moduli masses they find that the masses of the lightest moduli turn out to be close to the gravitino mass but less than twice the gravitino mass (the moduli cannot decay into the gravitinos by the kinematics). Then they note that this mass range is perfectly consistent with cosmology since the moduli are heavy enough to decay before BBN but the relic density must be non-thermal, etc, etc. What Kane is doing now is trying to extrapolate this result obtained for the non-perturbative G2 vacua to a “generic” string vacuum but I and many others don’t think that his reasoning is justified because there are well known counterexamples where scalars can be much lighter than the gravitino. However, what I would definitely agree on with Kane is that moduli stabilization in a generic vacuum combined with cosmological constraints greatly disfavors low scale gauge mediation scenarios.
Well, I actually just reread what Kane said in the paper and on Motl’s blog and the comments there and I guess I agree that in generic string vacua SUSY breaking is not sequestered, which translates into squarks and sleptons being as heavy as the gravitino. The known counterexample I had in mind was the KKLT scenario, where strong warping results in sequestering and light scalars and I admit that it is indeed kind of non-generic.
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Eric,
125 is right at the vacuum stability edge. if that turns out to be m_H, then there is work for a generation of lattice gauge theory to figure out whether the new physics scale in this scenario can be as high as m_planck.
but even if it might turn out to not be ok all the way up, the SM new physics scale will be well above 10^10GeV, maybe at about the GUT scale. so while there may be aesthetic reasons for low energy susy (fine tuning et al), there is no need. or, in other words, if m_H~125GeV and nothing else is found at the LHC, then any new collider below GUT scale energies will be a gamble: there is no strong reason to believe that it will find anything new.
Hi Chris,
Yes, I agree with you that a Higgs mass around 125 GeV is right on the borderline between being stable and unstable. Clearly, we’ll need more data before the picture becomes completely clear.
First of all, I think that Kane is grossly exaggerating what he and his collaborators have demonstrated. String theory at this stage can not make a firm prediction about the Higgs mass and I think that he is doing a great disservice to the community by this type of hype. That said, there is definitely something in their work that’s very intriguing and I’d like to highlight a few points below.
I think that it would be fair to say that string vacua that can be described in terms of N=1 D=4 supergravity with a low scale of SUSY breaking *generically* contain heavy sfermions and trilinear couplings but light gauginos (KKLT with warped sequestering is a non-generic counterexample). In addition, the masses of the lightest moduli are *generically* of the order the gravitino mass. These statementes would not be controversial among string theorists who know about moduli stabilization. On top of that, cosmological constraints imply that the moduli must be very heavy >O(10-100) TeV to preserve the success of the BBN. When you combine all of the above you may conclude that in such vacua even with low scale SUSY the lightest sfermions must be very heavy. What that means for the lightest Higgs in the context of the MSSM is that its mass will receive large radiative corrections mainly due to the heavy stop and will get pushed into the range above 120 GeV but below 130 GeV. Now, the exact value does, of course, depend on tan beta. With regard to tan beta being O(10) I’d recommend reading this paper: http://arxiv.org/abs/1105.3765 . Basically, tan beta ~ O(10) is needed to reduce the so-called little hierarchy problem when the scalars and trilinears are heavy, as can be seen from eq. 6 in that paper. So, the value of 127 GeV seems rather natural is such a scenario. Kane’s optimism about the gluino presumably stems from the same considerations, namely, in eq. 2, there is a quantity denoted as R(t), that depends on M3 (related to the gluino mass) as you can see in the expression in the paragraph below eq. 2. So, the relatively light gluino is needed if one wants to keep the little hierarchy problem under control.
So I think that this is all definitely very interesting and in my mind compelling.
As for the G2-MSSM, this is definitely the simplest model of moduli stabilization out there – a strongly coupled hidden sector (SQCD with a single family of vector like matter) dynamically generates a non-perturbative potential that stabilizes all the moduli and generates a hierarchically small scale (there are no fluxes, no warping, no antibranes). And these guys did it for the most general Kahler potential compatible with G2 holonomy with an arbitrary number of moduli, found closed expressions for the moduli and derived soft terms in the MSSM largangian!
Peter,
Yes, the “prediction” business appears disingenuous (and your post is one of the best I’ve read, which is saying a lot). But, in all fairness to Kane, there’s nothing wrong with a paper that identifies a subset of string theoretical models that accords with an experimental result or publishing it first. Just think of the vast swath of the multiverse and the numerous false vacua we can rule ourselves out of if we can identify a Higgs boson.
Wouldn’t you be impressed if string theorists were able to present at least one vacuum that resolves assymptotically to general relativity and the standard model? I don’t claim that string “theory” will get there, but isn’t constraining the “theory” using experimental results the best way out of the “string theory proves everything” hysteria?
Kane´s campaign still at full speed:
http://www.nature.com/news/particle-physics-is-at-a-turning-point-1.9675
Thanks Bernhard,
At least someone seems to have told him that there’s no way this is 5 sigma…
I like how he claims that he published his “significantly more precise prediction” “just days before the CERN data were reported”, without mentioning that it was four days after the CERN numbers were accurately reported on this blog and others.
Allan,
I just don’t see that the new Higgs result (if confirmed) does anything much to constrain string theory vacua. You still can get almost anything you want. After claiming that the 125 GeV Higgs shows his string theory arguments are right, he does go on to claim that this implies gluinos showing up in the data any day now, definitely by summer. When there are no gluinos next summer though, he’s just going to move on to other “string theory inspired” models. He has been engaging in this kind of nonsense for more than 25 years (see e.g his “String theory is testable, even supertestable” in Physics Today, back in 1997), with nobody calling him on it, no reason for him to believe they’ll start now.
Ah, I didn’t put Kane’s name together with that article. I see your point. Perhaps the best way to do string theory would be to publish papers in entangled pairs–for every prediction a lab makes, it should publish another paper predicting the exact opposite. That way they can accumulate a string (sorry) of predictions well in advance of the rumors.
So, I was looking at slide 24 (gluino production cross section vs gluino mass) in Gordy’s stringpheno 2011 talk: http://conferencing.uwex.edu/conferences/stringpheno2011/documents/kane.pdf
and I’m not sure if the LHC will actually collect enough data by the summer to really test for gluinos. Let’s say they collect 10fb^-1. From the plot, if the gluino mass is at, say 900 GeV, the production Xsection is 10 fb, which gives 100 events. However, taking into account the detector efficiency (at most few % according to the slide) is it realistic to expect some signal?
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