Two-sigmaish CMS multilepton excesses with a \(\tau\)

A possible hint of third-generation superpartners

Matt Strassler mentioned an interesting anomaly reported by CMS at a SUSY conference this week:

A Discrepancy to Keep an Eye On (Prof Dr RNDr Matt Strassler PhD CSc DrSc Dot COM)

It's small enough so that you may assume that it's just another example of a fluctuation that will go away with more data. But it's large enough for many of us to gain the right to be intrigued. ;-)



The excesses have something to do with multileptons. If you search this blog for multileptons, you find many articles, mostly from late year 2011 and early year 2012. The words "year" were inserted for you to notice that there were many hyperlinks in the previous sentence. It's plausible that those flukes have gone way during the 1.5-2.0 years.

What are the overrepresented events this time?




The CMS folks have performed a search for some signatures – at this point, it's not quite clear what comprehensive theory beyond the Standard Model they are testing but multileptons of course do naturally appear in long enough decay chains of supersymmetric particles (they are a strong hint that at least a pair of new particles was produced because they're almost absent in the Standard Model and in the decay of one new particle) – for events with four leptons and some of the subsets of these events exhibit modest but tantalizing excesses.




We're talking about events with four leptons including

• at least one \(\tau^\pm\) that decays to hadrons; I start with that to point out that the signal could have something to do with the third generation of fermions and their partners
• one light (\(e^\pm\) or \(\mu^\pm\)) lepton-antilepton pair (this is what OSSF1, opposite-sign-same-flavor-one, stands for) that seems not to originate from a Z-boson decay (because the Z-boson is assumed to be understood and boring; the condition is called "off-Z")
• the total energy in the lepton pair plus a few other jets quantified by a variabled called \(H_T\) should be surprisingly small relatively to expected LHC energies; this condition indicates a threshold above which a new massive particle was barely created
• another charged lepton, \(e^\pm\), \(\mu^\pm\), or \(\tau^\pm\)
• some missing momentum – which surely gets a contribution from the neutrino(s) that is (are) produced along with the \(\tau\) lepton but may also include the LSP etc.

A table that Matt reproduces for us has about 48 entries and 3 of them contain noticeable excesses. All of them are in the OSSF1, \(H_T\lt 200\GeV\), off-Z, \(N(\tau_h)=1\), \(N_{b\rm -jets}=0\) – bins with other options for these variables are really consistent with the Standard Model predictions.

The three bins with an excess only differ in the missing transverse energy:\[

\begin{array}{|c|c|c|}
\hline
E_T^{\rm miss} & {\rm predicted} & \text{observed}\\
& \text{events}& \text{events}\\
\hline
(0,50) & 7.5\pm 2 & 15\\
\hline
(50,100) & 2.1\pm 0.5& 4 \\
\hline
(100,\infty)& 0.6\pm 0.24 & 3\\
\hline
{\rm total} & 10.2\pm 2.1 & 22\\
\hline
\end{array}

\] Sorry if the error margins shouldn't have been added in quadrature; even if it is roughly correct, it's not the totally accurate way to account for the error margins. I guess that the right error should be between 3 and 4 events. I suspect that the errors in the table are just the systematic ones and the Poisson-type statistical ones \(\sqrt{N}\) must be added in quadrature manually. If you can clarify these issues, it would be appreciated.

At any rate, when you combine these three similar channels – naturally ignoring the magnitude of the transverse energy – you get something that may look like a greater than (or at least approximately equal to) \(3\sigma\) excess (because \(10.2\) and \(22\) are really far from each other). I don't want to say \(5\sigma\) which the sloppy calculation above could hint at because I don't believe this can be the right result.

I would say that the missing energy may be arbitrarily low in the events above so if an LSP is created, it should be a light one, safely below \(50\GeV\) – possibly the \(8.6\GeV\) dark matter particle suggested by CDMS II-silicon and others. And the superpartners created at the beginning of the reaction are likely to have something to do with the third generation – like staus. Or sbottoms...

This is not an excess you should think about every night at 3 a.m. so far. But it's an excess that you may return to at some point in the future and describe by the words that you already knew about it on August 29th, 2013, before the revolution got started.

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Tohoku, JP wins the International Linear Collider

The project may still be cancelled...

In June 2013, I discussed the contest between the Sefuri mountains and the Kitakami mountains who will build the International Linear Collider if any collider will be built. Recall that the former offered a sexy 4-minute musical video; the latter offered a somewhat boring, 21-minute-long educational video.

The "boring" video guys won! ;-) Congratulations to Hitoshi Murayama et al.

Tohoku pitched for ¥1 trillion [$10 billion] collider (JP Times)

---

Miyagi, Iwate prefecture mountains picked as possible site for int'l particle accelerator (The Mainichi)

The Japan Times tell us that 50% of the cost should be paid for by the host country and there seems to be some degree of skepticism in the newspaper and in the ministry of education etc.



83% of the overall expenses are construction costs; the rest is paid for land acquisition, salaries, and the production of the equipment.




I am convinced that $5 billion is a small amount for Japan that would earn a special status for the Land of the Rising Sun. Whether you like it or not, the state-of-the-art particle physics collider is still the #1 science project that turns the host country into a natural candidate for the headquarters of the world's pure scientific research. Even among non-friends of physics, I believe that the LHC contributes to the feeling that Europe is perhaps not quite entering the process of irreversible decay (in some respects, it's perhaps ahead of the U.S. and China etc.) and Japan could get revived in a similar way.




Incidentally, I want to mention that CDF and DZERO published a new paper on the top quark-antiquark forward-backward asymmetry,

Differential cross section \(\dd \sigma/\dd(\cos \theta t)\) for top-quark-pair-production in \(p\bar p\) collisions at \(\sqrt{s} = 1.96\TeV\),

where they insist on the existence of the strange effect and claim that the whole effect may be attributed to the first, "linear" spherical harmonic \(Y_{10}\). The other coefficients (up to something like \(\ell=7\)) of the spherical harmonics seem to be OK.

Thanks to Joseph S. for the links.

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Both neutralino, sbottom may weigh less than \(20\GeV\)

Dark matter searches and LHC rumors may converge in a light sbottom-photino point

I decided that the most exciting hep-ph preprint today is

Supersymmetry with Light Dark Matter confronting the recent CDMS and LHC Results

by Alexandre Arbey, Marco Battaglia, and Farvah Mahmoudi. An interesting detail about the list of the authors is that all of them are partially affiliated with the CERN theory division. Why is it interesting? Because the LHC top squark rumor from February 2012 was later rumored to have arrived from the CERN theory division so these three physicists might know much more about the superpartners accessible to the LHC than the rest of us.



They are inspired by the "positive side" of the dark matter wars and investigate whether the MSSM (Minimal Supersymmetric Standard Model) may predict the LSPs (Lightest Superpartners: the supersymmetric theories' candidates for the WIMP dark matter particle, in most cases) that are as light as \(10\GeV\) or so. Note that the most accurate figure suggested by the "coalition of the willing" is \(8.6\GeV\) by CDMS II Silicon.




At any rate, the new CERN theoretical paper argues that in contrast with the unproven assumption in the bulk of the MSSM literature (that superpartner masses are above \(100\GeV\)), this very light new particle that the dark matter direct search experiments are perhaps seeing could be the ordinary neutralino from the MSSM, the simplest and most widely studied supersymmetric model of particle physics.

The late LEP collider that used to work in the LHC tunnel until 2000 (LHC's song) has measured the invisible width of the Z-bosons – the number of times when this boson decays to invisible final products – and it hasn't found anything. It means that such a light hypothetical LSP can't be interacting with the Z-boson too strongly. Consequently, it must be mostly photino, a state that is perpendicular to the zino.




This is my wording which, I believe, reflects a more appropriate choice of the basis than the bino/wino dichotomy. The usual 2-dimensional basis in the space of the neutral colorless gauge bosons consists of the photon and the Z-boson and you may consider their superpartners, the photino and the zino. It's perhaps more natural because the fermionic superpartners get contributions to their masses from the Higgs mechanism, too (and not just from SUSY breaking). Because the \(Z\to \tilde\chi^0_1\tilde\chi^0_1\) must be suppressed (the superscript zero is the electric charge; the subscript labels particles of a similar kind from the lightest so 1 means the lightest one in the group), it follows that \(\tilde\chi^0_1\), the lightest neutralino (which happens to be the LSP), must be nearly a photino.

Because the photon is "mostly" the \(U(1)_Y\) B-boson while the Z-boson is "mostly" the \(W_3\) neutral W-boson, we may also say (and they do say) that the LSP in their scenario is mostly the bino. In the popular MSSM scenarios, the LSP is on the contrary mostly a neutral wino. As I said, I think that we could be shown that it's more natural to keep the basis photino/zino for the superpartners as well and the LSP discussed in the paper could be almost exactly a photino.

Such a light LSP would lead to various contradictions in the generic case but all of them will be solved with the extra assumption stated in the next paragraph. Moreover, the very light LSP would generically have a too tiny cross section with the nucleons which would make it impossible for these photinos to show up in the dark matter direct search experiments.

Both problems are solved if the NLSP (Next to Lightest Superpartner i.e. the second lightest supersymmetric partner) is the mostly right-handed sbottom, \(\tilde b_R\), with the near-maximal mixing angle around \(\pi/2\). If the mass splitting is\[

M_{\tilde b_R} - M_{\tilde \chi^0_1} \lt 7\GeV,

\] then the nucleon-WIMP cross section is pleasantly increased, some unwanted processes are suppressed, and everything seems OK. For the light sbottom, they mention their preferred mass range \(15\)-\(25\GeV\). But if you assume that the LSP sits near \(8.6\GeV\), the CDMS II Silicon figure, then you may see that the light sbottom should be lighter than \(16\GeV\) or so.

The lighter top squark should be between \(600\GeV\) and \(700\GeV\) in this picture. The lower bound follows from the stop's absence in some LHC searches; the (less certainly known) upper bound is required to preserve the stability of the Higgs potential. The heavier, mostly left-handed sbottom is another \(100\GeV\) or so above the top (or at least not far). The second lightest neutralino and the lightest charginos are between \(150\) and \(1,000\GeV\).

I think it would be lots and lots of fun if the LHC began to discover the superpartners starting from the very light photino and bottom squark. Such a possibility seems to be consistent with all LHC constraints, with the positive hints suggested by the dark matter direct search experiments, and perhaps even with the rumors that the LHC may have been seeing some hints of third-generation squarks for some time and that the CERN theory division is the environment that may be ahead of us in the knowledge of this breakthrough. ;-)

To parameterize the possibilities, the paper is employing the pMSSM, the 1999 phenomenological MSSM i.e. the MSSM's bottom-up phenomenology-inspired (19 masses of superpartners quantifying) subspace of the parameter space, that is more viable than the nearly excluded, top-down-inspired (but equally dimensional) CMSSM ("C" for "constrained") / mSUGRA (Minimal Super Gravity) subset and that is likely to spread in the SUSY model building literature in the foreseeable future.

In most of the typical MSSM literature, the superpartners were always reorganized to charginos, neutralinos etc. and treated independently of their known superpartners. I increasingly feel that this may have led to an unnecessarily generalized choice of the bases.

Instead, it's plausible that the simple superpartners of the known particles, including the photon and the Z-boson, could produce a more realistic basis. It seems very natural to me to believe that the photino isn't too heavy i.e. isn't too far from the (vanishing) mass of the photon; the zino isn't "too" (more than a factor of 4 heavier) far from \(90\GeV\); and the sbottom and the stop aren't too far from the masses of the third-generation quarks, either. In fact, the Wildlife Supply Company already offers you a $47 plastic tool to replace all bottom quarks in an object by comparably light sbottoms (see the amazon.com link). With this logic taken seriously, I would also expect the stau[s] (tau slepton) and the tau sneutrino to be relatively light; the assumption is that the particle-superpartner mass proximity doesn't apply to the first two generations and gluons-gluinos.

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SUSY, a scapegoat: different kinds of belief

...much of the anti-SUSY propaganda is unbelievable...

One week ago, I argued that it is totally inappropriate to use the adjective "speculative" for theoretical frameworks such as supersymmetry.

It's a topic that's being discussed at many places which is why now, one week later, I will reopen these issues. Two days ago, Alok Jha of the Guardian wrote his text

One year on from the Higgs boson find, has physics hit the buffers?

and it was discussed at a leading HEP crackpots' website where Giotis, Urs Schreiber, and others kindly debate some nasty and stupid physics haters. Incidentally, the subtitle in Jha's article calls SUSY "the elusive followup theory to the Higgs mechanism". First, it isn't the only or most accurate way to describe SUSY which is mostly independent of the Higgs issues. Second, it isn't "the" only followup theory to the Higgs mechanism. Third, if it were "the [right] followup", it shouldn't be shocking if we need more than 1 year after the discovery of the Higgs boson to discover SUSY. One year is a short time in the history of physics.

But the basic point that Giotis began to emphasize to these demagogues is that the existence of SUSY in Nature and the discovery of SUSY at the LHC are two completely different questions. The LHC is an accelerator that allows us to reach energies that are one order of magnitude greater than the energies accessible at the previous top collider, the Tevatron. But even at the logarithmic scale, you would need to make about 15 analogous steps to get close to the fundamental scale (or the string scale).

The LHC may look expensive to some people but it's just far from a tool allowing us to directly test the most fundamental questions about Nature. Whether this increase of the log(energy) by 1/15 of what we would like is enough to find groundbreaking discoveries isn't and couldn't be clear. The LHC has found the Higgs boson and it is not "impossible" that this is it.




Columbus may have seen no traces of a new (or old and exotic) continent 2,000 kilometers West from Spain but that didn't imply that there were no new continents in that direction.

In Spring 2007, I listed some probabilities of different ambitious propositions in high-energy physics. It's still about right but I would say that my numbers were slightly optimized to be acceptable for the bulk of high-energy physics theorists. At any rate, you see that the probability that string theory is right is closer to 100% than to 50% (I would insert a higher number today); the probability of SUSY at the GUT or lower scale was quoted as 70% (and yes, I would write the same number today, with most of the remaining 30% corresponding to SUSY that only gets restored between the GUT scale and the Planck scale); and the probability of SUSY at the LHC was 50%. Note that it has never been "guaranteed" that the LHC would see SUSY and almost none of the SUSY champions has ever claimed such a thing. I surely haven't. I have always viewed SUSY at the LHC as a "damn plausible" possibility which is worth thinking about because it's so exciting.

Science produces insights, people write new papers, they have time to think about the old ones, so the probabilities are evolving. But there has been no complete revolution since 2007 so the current numbers are qualitatively the same. Of course that the probability that the LHC will find SUSY has moderately decreased because the LHC has already depleted a fraction (but far from 100%) of its ability to find new physics. The claims that theorists are completely negating their logic and circumvent the rules are just lies.




Now, of course that it would be great fun if the LHC started to produce tons of new physics. But something's being "fun" is a totally different thing from its being true – and from its being a prediction of a theoretical framework. Individual models may predict SUSY at the LHC – and parameter spaces of these theories may at least claim that "SUSY at the LHC is very natural". But it is not really clear which of these parameter spaces of classes of theories is right so science in general isn't able to predict when the supersymmetry or any other example of new physics will be discovered with any certainty at this point – and whether it will be at the LHC.

Ben Allanach, a top SUSY phenomenologist, said the following to the Guardian:

If the worst happens, and supersymmetry does not show itself at the LHC, Allanach says it will be a wrench to have to go and work on something else. “I’ll feel a sense of loss over the excitement of the discovery. I still feel that excitement and I can imagine it, six months into the running at 14 TeV and then some bumps appearing in the data and getting very excited and getting stuck in. It’s the loss of that that would affect me, emotionally.”

It's obvious and right that folks like Allanach are excited according to the experimental data that are arriving. Again, excitement is something else than the truth, too. Truth may seem unexciting for quite some time but it's still the truth and to find a new great truth, one (and the mankind) often has to be very patient, clever, and hard-working. By the way, by "something else to work on", Ben Allanach surely doesn't mean "other kinds of new low-energy physics" because this will have been largely falsified, too.

At any rate, the supersymmetric model building isn't the only part of research of SUSY or the only body of knowledge we have about SUSY. SUSY is a much grander principle whose importance goes well beyond the LHC and its limits. It seems necessary to produce fermions, ban tachyons, and improve some hierarchy-like problems according to the only known (and, most likely, the only mathematically possible) unifying theory of quantum field theory and general relativity – an overarching theory we still call string theory. From this broader, top-down viewpoint that I prefer, phenomenologists are just "engineers" who are working on specific ways to discover SUSY (and questions what exactly will be seen) in the near (or not so near) future.

But the SUSY research doesn't really boil down to these phenomenologists' work and it didn't start with that.

In the early 1970s, SUSY began in the USSR when some mathematical physicists asked whether spacetime symmetries greater than the Poincaré symmetry may be compatible with everything we know; and it started in the West when Pierre Ramond decided to incorporate fermions to the (previously) bosonic string theory. The Soviet guys found exactly one possible extension of the known spacetime symmetries, a graded Lie algebra known as supersymmetry. And Ramond found out that the world sheet SUSY was needed to add the fermions to string theory. Later, Ramond's (and Neveu-Schwarz's) string theory was shown to predict spacetime supersymmetry, too (with GSO projections). Years before that GSO's development, people walking in the footprints of Wess and Zumino were already building 4D supersymmetric quantum field theories. In the early 1980s, other folks like Savas Dimopoulos and Howard Georgi – soon accompanied by folks like Gordon Kane and Howard Haber – were reconciling supersymmetry with the Standard Model and looking what new things result from this union.

Of course that the Standard-Model-like supersymmetric models are the most relevant ones for the interpretation of likely and plausible experimental signals in the near future. But they're far from being the most fundamental supersymmetric models. Even in our Nature, SUSY is almost certainly realized by a more comprehensive theory than the MSSM – at least if you want to include higher-energy phenomena.

In the more formal QFT and string theory research, SUSY has been essential for most of the important other developments in the last 30 years, too. It was needed to make grand unification really convincing (due to the coupling unification in MSSM). It was needed to calculate some quantities that established dualities (S-duality, U-duality, Seiberg-Witten analyses of gauge theories), it was essential for the twistor prescriptions for gauge theories, to calculate the correct black hole thermodynamics from a microscopic theory, to establish and study almost all specific theory pairs in AdS/CFT. Matrix theory requires SUSY as well and there are many more examples. SUSY cures or improves certain "systemic" inconsistencies and hierarchies and the modern research has simply shown that "Yes SUSY" is a better default assumption than "No SUSY". The progress leading to this paradigm shift was theoretical in character but it was totally scientific, anyway.

The continuing validity of the Standard Model is just another example of the wisdom that successful theorists often underestimate the range of validity of their own theories. This 1994 paper by David Gross summarizing the 1938 Warsaw conference showed lots of confusion that was around at that time. With the shining exception of the early de facto string theorist Oskar Klein, all top physicists were eager to falsify quantum mechanics and/or quantum electrodynamics at nearby scales, typically the Compton wavelength of the electron (distance in between the size of the atom and the nucleus). Of course that we know that the validity of QED goes much further than that. Those big shots should have taken their discoveries more seriously than they did. Sometimes old physicists who have already achieved enough want the younger theorists to share their relatively simple path to fame and wealth but Nature isn't obliged to obey. After some discoveries, it may often take a longer time for new discoveries to emerge. It's not necessarily the current physicists' fault; it's often just a fact about Nature's inner workings.

The case of the Standard Model may very well be analogous. People are obsessed by the wishful thinking that they will see lots of discoveries in the rest of their lives which is an assumption requiring that the discrepancies between the experiments and the established theories will be found rather soon. But it doesn't have to be the case. However, if the discrepancies aren't found quickly, it doesn't mean that there is no new physics or the search for new physics is futile. It just means that Nature eventually forces us to be more patient as She unmasks that some guesses about the speed of new discoveries were too optimistic. The "right amount of patience" is something that only Nature is allowed to determine and we ultimately learn what the amount was. It's totally dumb to impose any Stalinist or Smolinist five-year plans or five-year deadlines if we really don't know where (how far) Nature has hid the new treasures.

Phenomenologists who made bets on new physics around the corner shouldn't be surprised. If 1,000 phenomenologists propose 1,000 different, inequivalent models for new physics beneath a threshold, e.g. 1 TeV, then it's guaranteed that at least 99.9% of them would ultimately be shown wrong. We didn't need the LHC to arrive to this conclusion. High-energy physics was producing lots of hypothesized and competing models of new physics because the development of these ideas was still cheaper than the construction of the experimental gadgets (the price of the LHC equals 100,000 annual salaries of a phenomenologist – e.g. 1,000 phenomenologists funded for 100 years which is a lot of papers, of order 100,000 as well). This price comparison (the fact that relevant HEP experiments have become relatively expensive) is the reason why it's inevitable that model builders have probed many possibilities in advance, most of which are guaranteed to be excluded by the LHC, so the composition of the phenomenological literature was guaranteed to paint a "too optimistic" projection of the coming experimental discoveries of new physics. These comments seem sort of obvious to me, I have always kept them in mind, but it seems that many other people were not.

In each article of this sort, I have to emphasize that SUSY is just treated as a scapegoat. The LHC data are compatible with the Standard Model so far which reduces the probability that any theory of new physics that is too radical is right; the LHC razor cuts through the space of possibilities within each paradigm of new physics. SUSY is the most well-motivated principle of new physics but among the experimentally relevant proposals of physics Beyond the Standard Model, SUSY is not being hurt more than others. In fact, just the opposite is true: the relative weight of SUSY in the signals of new physics that have a chance to be found first is increasing as other theories are being excluded more "sharply" than SUSY. It's something we have known before the LHC began its operations, too.

John Ellis is quoted by the Guardian:

John Ellis, a particle theorist at Cern and King’s College London, has been working on supersymmetry for more than 30 years, and is optimistic that the collider will find the evidence he has been waiting for. But when would he give up? “After you’ve run the LHC for another 10 years or more and explored lots of parameter space and you still haven’t found supersymmetry at that stage, I’ll probably be retired. It’s often said that it’s not theories that die, it’s theorists that die.”

The claim that theorists die but theories do not is catchy and cute but I don't really think it's an accurate description of the real world. Physicists are sometimes right, sometimes wrong, sometimes they die, sometimes they are born, sometimes they share their opinions with similar physicists, sometimes they don't, sometimes they're more right than younger physicists, sometimes they're less right than younger physicists, and so on. There isn't any general rule that would say that older physicists have to be wrong or something like that.

Moreover, what the death of old theorists is good for in most cases isn't really the death of wrong theories. Instead, the death of old theorists is often needed for the new and better theories to be allowed to live. Physicists like Albert Einstein would decelerate the progress in quantum mechanics if they were around for too long and in too high numbers; physicists like Paul Dirac would discourage younger physicists from computing renormalized corrections in quantum field theories because they didn't "believe" renormalization; physicists I could name but I won't name would slow down or cripple the research of string theory if these old chaps weren't dying sufficiently quickly, and so on.

I have already mentioned that in some cases, the old theorists are too conservative in the sense that they're no longer able to absorb the new theories and their logic, so they just use their authority to "refuse" them and be loud about it. On the other hand, I have also mentioned that old theorists often tend to expect more speedy revolutions than what Nature actually recommends. So old theorists may err in both directions. It's silly to assume that they always err in the same way. If this were the case, they would have to be completely stupid not to learn anything from similar if not "always the same" mistakes by their predecessors.

What I need to point out about Ellis' indication that he won't say that SUSY is wrong in his lifetime is that as far as I see the reality, he simply has very good scientific reasons to keep his opinions. It's something I have explicitly said many times myself. Long before the LHC began its operation, I was saying that the LHC may find no new physics but I would still be confident that string theory and SUSY are right in Nature.

It's pathetic for the aggressive cranks to interpret Ellis' words as a sign of dishonesty. The data coming from the LHC show that the proponents of any new physics have to be more patient than the (strongest) optimists were expecting. The data don't selectively imply that SUSY is wrong simply because SUSY models compatible with all the data exist. They just imply that the Standard Model is useful and accurate enough in a larger class of contexts but we know it's not quite accurate so it's a matter of when and what, and not if, the new physics starts to emerge. You can't rule out a well-defined theory such as a class of SUSY models differently than by falsifying it, by showing it's wrong, by finding a contradiction. Vague demagogic slogans about their "not even wrong" aren't enough for well-defined theories. Wolfgang Pauli has used the "not even wrong" slogan for largely ill-defined (and also fundamentally misguided because postulates-of-QM-denying) musings by David Bohm, not for a Pauli-style well-defined physics ideas such as SUSY. It's really an example of chutzpah to use Pauli's dismissive anti-Bohm slogan against a theory of the very kind that he would love (or discover!) if he hadn't died in 1958 (symmetries depending on the spin in new ways – which other physicist in the 1920s would have loved that?).

The Baltic American counterpart of Alexander Unzicker has not only offered this nasty and unfair criticism against Ellis. He also wrote:

The LHC will be in operation until 2030 or so, and you can always start arguing that 100 TeV will be needed to see SUSY (see here), ensuring that giving up won’t ever be necessary except for those now still wet behind the ears.

You see that it's a disgusting and dishonest demagogy, the kind of demagogy that the scum that keeps on reading that blog likes to hear. The single word that is most dishonest about the quote above is "start". People won't start to claim that 100 TeV is needed to (almost reliably) see SUSY. They have always claimed so. Some relatively recent phenomenological advances made the sub-100-TeV scale even more attractive. There are numerous reasons to think that something should be happening over there.

After all, the Superconducting Supercollider that was canceled almost 20 years ago was supposed to have the center of mass energy equal to 40 TeV which is pretty much of the same order as 100 TeV. So it's completely unfair to suggest that it would be a sign of the theorists' arrogance and their changing of the rules during the game if they wanted a 100 TeV collider in 2015. They – we – have always wanted one. It was the default energy scale for the accelerators that the theorists were actually planning. Political reasons forced the theorists to be satisfied with a 13 TeV collider more than 20 years later and many theorists would say that it could be enough to see new physics, too. But no doubt about that, at 13 TeV (or even 7-8 TeV), the risk that no new physics is found is of course higher than it is at 40 TeV.

I want to say that the suggestions by Shmoits and many similar people that the theorists are moving the lamp posts towards high energies is partly a lie, partly a tautology. It's partly a tautology because high-energy physics is about the research of high-energy phenomena and the more it knows, the more it moves towards higher energies. So some trend towards higher energies is inevitable as we're learning more. On the other hand, the "next big step" that the theorists were contemplating (and they were already building the collider) was always close to the vicinity of a TeV or dozens of TeV and if something has changed about this energy scale, it went down since the early 1990s or so, not up. Of course that there are also particular models that predicted new physics at low enough scales that would have shown up at the LHC by now but it didn't. They're excluded or their parameters have to be shifted towards less natural, heavier values. This is an inseparable part of learning: it's inevitable that there have to be periods in which the old theories just work so some specific enough scenarios with new physics have to be ruled out. But there are many classes of theories for which this hasn't really taken place.

People have been telling me about some advantages of precision machines, not too high-energy colliders and factories, and I have never bought into them. The energy frontier is still the most important place for progress. To increase the colliders' energy is the most natural way to increase the probability of new discoveries. This will probably be the case after the LHC, too. I am totally confident that the bulk of good phenomenologists agrees with me (I think that e.g. Nima Arkani-Hamed surely does).

Once the SSC was canceled, phenomenologists were sort of externally forced not to talk about "truly" high-energy colliders and these high energies themselves. But I don't really care. The cancellation of the SSC is an item in the history books and it doesn't mean that the mankind won't ever be allowed to build a super-20-TeV collider again. I don't find the old story too important today. The politicians don't have the power or the moral right to eternally constrain the scientists. They only decide about things at the timescale of their term. At longer timescales, things may be different. Of course that I want a 100 TeV or so collider. I have always wanted one but in the near future, due to some progress in the technologies, a real-world-priced collider that is this strong will become feasible again.

The ideas that one should "give up" this and similar research are really recommendations to abolish high-energy physics as a scientific discipline. There isn't any scientific evidence that this is sensible. Instead, the scientific evidence is overwhelming that the people proposing such things are dishonest stinky scumbags.

What I find unbelievably irritating are P.R.-like proclamations by individuals such as the crackpot-in-chief:

Urs, The problem is more your use of language, since if you made it clear to people that when you said “supersymmetry”, you meant something that can’t ever be tested, they wouldn’t take you very seriously. I think you’re right that some string theory/SUSY enthusiasts post-LHC will argue that nothing has shown them to be wrong, and nothing in their lifetime ever possibly can, but to the extent that they make this situation clear they will have a serious credibility problem.

What this jerk doesn't understand – or understands but doesn't want to admit – is that scientific theories aren't judged by their being taken seriously by brainwashed violent imbeciles among the laymen, the kind of low-brow primates who keep on devouring "Not Even Wrong" and similar feces and happily smack their lips at the same moment. Science is accepting or eliminating hypotheses according to the best scientific evaluation of the available evidence.

The available evidence makes it more reasonable to be convinced that SUSY is a part of Nature and unless a clear discovery occurs in the near future, a few years of extra experiments only have a modest ability to change the scientific opinions about this question because the experiments we can pay for today are simply not and cannot be machines that directly and "reliably" touch God's face. SUSY may turn out to be experimentally inaccessible by the LHC but the same would clearly be true about the non-existence of SUSY. So the evil people's belief that SUSY isn't out there is equally "unscientific" according to their own criteria – of course that these malicious kibitzers never apply their own rules to themselves.

Much of the science as we know it is about effects that we're certain or reasonably confident about but we can't directly experimentally test them. The closer we move towards the cutting edge, the higher percentage these "untestable" insights and hypotheses represent. Their being "untestable" in the most naive sense doesn't mean that they're not valuable. Many of them, including SUSY, are precious. One can be a completely uneducated, uncultural, brainwashed person who isn't able to understand these facts but these idiosyncrasies can't invalidate the facts. Columbia University's copy of Alexander Unzicker has been saying for years that in this sense, "[practically, now] untestable" ideas can't be an essential (or even legitimate) part of science. But what he has been saying has always been a lie, it is still a lie, and the people who haven't been able to figure out that this main thesis sold by the populist is rubbish have always been severely limited morons, they are still severely limited morons, and they will remain severely limited morons. Science has never worked according to their primitive recipes and to make things worse for them, science's distance from these recipes is increasing with time because our deepening understanding of the space of ideas allows scientists to separate credible theories and hypotheses from the raw experimental data by ever longer chains of derivations and implications.

Similarly, it is not the scientists' job to avoid a "credibility problem" with stupid and dishonest people who have no idea, especially with people who haven't even been capable of figuring out that Shmoits' rants are pure trash. Science is something completely different than P.R. This mediocre scum has gotten used to the situation in which their dirty buttocks are being licked by the populist politicians and media every day and everything must be according to the random desires of these degenerated spoiled brats. But as long as science remains science, it will carefully avoid this kind of external control. You don't find SUSY theorists "credible enough", stupid and nasty "Not Even Wrong" reader? Why don't you eat your own excrements to get some relief? The people who are telling you that science proceeds according to its looking "credible" to your random mood swings and vitriolic fads are not scientists even though sometimes they love to fraudulently create the impression. They are hardcore demagogues of the Shmoit kind – garbage like you. Thank you.

As a bonus, to expose the characteristic "quality" of the science by the anti-SUSY kibitzers, let me quote a comical crackpot called "N. Takanishi" at "Not Even Wrong":

Giotis, Three decades ago, I proved that SUSY cannot be the fundamental symmetry of physics. The reasoning is as follows. Evidently, SUSY, if it exists, must be spontaneously broken, but there is no Nambu-Goldstone fermion. Hence, one must assume that super-Higgs mechanism works. That is, supergravity must be encountered. However, quantum supergravity cannot be consistent with SUSY. This is because the global super-charge generators have no space-time index, while the translation generator P_mu does have a space-time index in contradiction with the SUSY anticommutation relation.

And it goes on and on and on. You see that he (or she) says that the supercharges have no spacetime indices. If he had asked his high school teacher, he would have known that supercharges have a spacetime index, a spinorial one. That's indeed needed for the SUSY algebra to be OK under the Lorentz symmetry and to have a spacetime vector (the momentum) on the right hand side. Completely rudimentary misunderstandings and ignorance – and I would say stupidity at a totally hopeless level – is what underlies the sand castle built by the anti-SUSY Mujahideens.

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Ex-HEP climate scientist urged to get arrested, hesitates

This article in the Guardian offers us quite an amusing combination of climate science and particle physics:

Climate scientists must not advocate particular policies

That's the main message we hear from Tamsin Edwards, a climate scientist in Bristol. She reminds us of something you've heard many times on this blog: science cannot answer moral questions. It can't even tell you whether you should have a carbon tax or fight for a wetter atmosphere, among many other things. Scientists who violate this rule inevitably reduce the credibility of science in general, especially if and when there are sensible concerns that the political considerations and goals could have determined the scientist's manipulation with the data. Right.

A scientist is also a human with her human rights so she can think and say whatever she wants about many political and other issues – at least, in the genuinely free world, she can – but she just shouldn't sell her political opinions as conclusions of scientific research (or as "scientific consensus" as these political statements are often called). This interpretation is an abuse of science.

If you were ever denying that the climate scientists are being politically pressured, well, she reminds us that she and her colleagues are repeatedly urged to be persuasive, be brave, and get arrested ;-), whenever necessary. She apparently doesn't want to get arrested. By the way, you may learn several other embarrassing things about the climate pressure groups and their pathological interactions with the climatological community from her essay. So far, researchers such as herself aren't being collected in special AGW Kamikaze units.




At the same moment, she says that many people began to appreciate her – a self-evident lukewarmer (who often identifies herself with Roger Pielke Jr) – as an honest broker even though her opinions are "completely mainstream". Well, are her opinions completely mainstream? Surely not according to those activists who are overwhelming us with the meme that 97% of the climate scientists want (and must verbally support) a carbon tax or a cap-and-trade system and who will probably flood her mailbox with some hate mail once they read her essay and learn that it was positively mentioned at the denialist ;-) blogs such as The Reference Frame.

I apologize in advance for my contribution to the hate mail but I also kindly emphasize that this contribution is zero – 100 percent should be blamed on the authors of the e-mails and their agenda.




According to the actual present composition of the climate science community, especially the loud and media-savvy part of it, she is not mainstream in any sense. Such people wouldn't dare to name their blogs "All Models Are Wrong". This is almost the ultimate heresy, isn't it?

She considers herself completely mainstream, pro-science, and feels confident that she is in charge of her research. Yet, she clearly contradicts the climate orthodoxy. Where could such a researcher come from? Try to guess! ;-) This is not a rhetorical question. It's a real question with a very interesting answer. If you look at her page at academia.edu or one in Bristol, you will find out what she used to be in her previous life. You will notice articles such as her PhD thesis,

Diffractively produced Z-bosons in the muon decay channel in \(pp\)-collisions at \(\sqrt s={1.96}\TeV\), and the measurement of the efficiency of the DØ Run II Luminosity Monitor

Yes, Ladies and Gentlemen: her PhD (2006) is from experimental particle physics and she has worked for the Fermilab. In her essay in the Guardian, we can't learn about that but what we can learn is that she switched to climatology because she cared about the environment. (Not getting a job in high-energy physics could have encouraged her to pursue a new career, too.)

Even some of the most impartial and independent climate scientists – those imported to the discipline from the Fermilab – were motivated by political or ideological goals when they were deciding whether they would start to do the research of climatology. Just to be sure, if climatology were a full-fledged science, people would study it not because they care about the environment but because they want to understand how the climate system has worked, is working, and will work.

Be sure that your humble correspondent cares about clean Nature at least as much as she does. I have spent weeks by the work helping the trees in the Bohemian Forests, for example. I have virtually no emissions of harmful gases and even no emissions of the gases that are beneficial but are being slung mud at (carbon dioxide). But I do care about science and its integrity and it seems that so does she.

It's hard to imagine that Dr Edwards won't learn how distorted her new discipline has become. She will and even if she does believe – for irrational reasons – that CO2 is dangerous in any sense, she is bound to become a skeptic of her own sort. You can't avoid becoming a skeptic of a sort after you publish a hardcore blasphemy in the Guardian and she hasn't done anything less than that.

I learned about her article from Real Climate. So far, the Real Climate comments about her text seem to be favorable and that's also true for the comments under the Guardian article. However, you will see that she's been attacked over there by some predictable suspects, e.g. Greg Laden.

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LHCb: \(3\)- or \(4\)-\(\sigma\) excess of \(B\)-mesons' muon decays

New physics may already be looking at us

Tommaso Dorigo has discussed something that may be interesting – a hint of new physics coming from the LHCb experiment:

A Four-Sigma Evidence Of New Physics In Rare B Decays Found By LHCb, And Its Interpretation

The deviation will be described in the LHCb-PAPER-2013-037 paper, now in preparation. Locally, it is a \(3.7\)-\(4.0\sigma\) effect which is reduced to \(2.5\)-\(2.8\sigma\) once you take the 24 bins into account (look-elsewhere effect). See page 13 of Nicola Serra's presentation in Stockholm.

We just described how strong the evidence is. But what events is the evidence about? Well, it is about the decay of the neutral \(B\)-mesons\[

B^0 \to K^* \mu^+ \mu^-, \quad K^*\to K^+ + \pi^-.

\] Recall that the asterisk denotes a virtual particle in this experimental jargon. When some "new observables" are used, they see the aforementioned excess of events approximately in bins with the transferred momentum\[

1\GeV\lt \sqrt{|q^2|}\lt 3\GeV

\] or so, especially between \(2\GeV\) and \(3\GeV\).




Dorigo recommends you a three-day-old hep-ph paper by Sebastien Descotes-Genon, Joaquim Matias, and Javier Virto

Understanding the \(B\to K^* \mu^+\mu^-\) Anomaly

This paper is aware of the anomaly we have mentioned and proposes a parameterization of the anomaly – some new physics' contribution to the "Wilson" coefficient \({\mathcal C}_9\) of the semileptonic operator\[

{\mathcal O}_9 = \frac{e^2}{16\pi^2} (\bar s\gamma_\mu P_L b) (\bar \ell \gamma^\mu\ell).

\] The operators with subscripts \(7\) and \(10\) are discussed, too. Who is contributing to the coefficient isn't really clarified so this whole discussion remains somewhat boring and technocratic.




However, some TRF readers with a very good memory should have a deja vu feeling. Haven't we seen something similar?

Yes, we have. First of all, in May 2012, BaBar reported a \(3.4\sigma\) excess in \(\tau\nu\) decays of the B-mesons. But the \(\tau\) leptons were involved so it's a different final state than the final states considered here.

In March 2013, I described some potentially huge, \(7\sigma\) or \(9\sigma\) excesses in pion and kaon decays of the charged \(B\)-mesons seen by the LHCb. Note that journalists often present each experiment that agrees with the Standard Model as strong if not lethal evidence against new physics but they get it upside down: it's enough to find one experiment that disagrees with the Standard Model to falsify that good old theory and it's plausible that we already know such experiments.

Most similarly, in November 2013, Gordon Kane wrote a TRF guest blog about the superstringy predictions for the\[

B^0_s\to \mu^+\mu^-

\] decays which are similar to the decays discussed in this text but they didn't including the virtual kaon. The stringy prediction looked very accurate to them (LHCb and CMS just published their combined data on this very process that are compatible with the Standard Model) and the processes mostly depended on the moduli – the scalar fields encoding the oscillating shape of the compactified dimensions whose particles should be at least as heavy as \(30\TeV\) or so for cosmological or astrophysical reasons.

So some evidence of new physics may already be "out there" but time and independent observations will probably be needed before we will feel any certain about these claims – and, equally if not more importantly, about the type of new physics that causes these anomalies.

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Naturalness and the LHC nightmare

Phil Gibbs wrote a nice essay,

Naturally Unnatural,

in which he discusses the annual EPS-HEP conference that just began in Stockholm and the subdued/nightmare feelings that phenomenologists may have due to the perfect agreement between the LHC and the Standard Model. He adds comments about naturalness and the multiverse.



Unnaturalness is sometimes in the eyes of the beholder.

Nima is quoted as a defender of a \(100\TeV\) collider. A possible result could be that nothing new is found which would be considered fascinating by Nima because that would be a proof of some unnaturalness in the Universe. Well, I have been defending "ever higher energies" as the most well-motivated post-LHC direction of particle physics for quite some time but I wouldn't be too thrilled by a negative result. It seems totally plausible to me – the probability is comparable to 30-50 percent, whatever – that the Standard Model would work even at such a higher-energy collider.




The reason is that I have never had any trouble with a modest amount of "unnaturalness". Many dimensionless quantities in physics are of order one but there's nothing impossible about quantities' being of order 0.001 or somewhat smaller.




Although this point has been analyzed many times on this blog, let me add a few words.

Unless we have a more accurate way to estimate or calculate a quantity \(g\) which is a priori between \(0\) and \(1\) – let's normalize it in this way – it's rather natural to choose the uniform prior probability distribution in which the probability that \(g\) is in the interval \((g,g+dg)\) is simply \(dp=dg\). In particular, the probability that \(g\) is smaller than some very small \(g_0\) is of order \(g_0\) itself.

Neutrinos: T2K shows electron-muon neutrino oscillations at 7.5 sigma...

That's the real reason why we don't expect the dimensionless parameters – that probably result from some more fundamental physics – to be much smaller than their "natural" value. It's all about the Bayesian inference and some prior probabilities.

However, this uniform prior probability distribution is rather unrefined and naive. It reflects our ignorance. It's very clear that if we knew more about the physical phenomena that determine the value of the parameter, we could also know that these phenomena favor low values so that the probability distribution could be, for example\[

dp = dg\cdot \frac{g^{-k}}{1-k},\quad 0\lt k \lt 1

\] which makes the values of \(g\) near zero much more likely. Alternatively, a better theory may also predict that the right probability distribution is\[

dp = dg\cdot \delta\zav{ g - \sqrt{ \frac{4\pi}{137.036} }}

\] i.e. a distribution that simply tells you the right value of the constant. The original uniform distribution wasn't fundamentally true in any sense. It only reflected our immediate knowledge about the system and the distribution was uniform because we had minimal knowledge about the question. It's clear that a theory that gives non-uniform distributions, especially one that produces the delta-function-like distribution, is more predictive, more refined, and unless falsified, may be much more correct and accurate than the "theory" producing the uniform distribution.



Is this animal unnatural? The main reason why most people will say Yes is just their lack of experience with it.

I used the number from the fine-structure constant because it's going to be my example. It is equal to\[

\alpha = \frac{e^2}{4\pi\epsilon_0\cdot \hbar c} \sim\frac{1}{137.036} \sim 0.007297

\] and this dimensionless number quantifies the characteristic strength of one of the most familiar fundamental interactions, the electromagnetic force. Note that the value is also "much smaller than one" and we could say that it is rather unlikely (less than one percent probability). However, with some extra knowledge, we may argue that the value isn't too unnatural. Why?

First of all, we might argue that \(\epsilon_0\) is more natural than \(4\pi\epsilon_0\) in the rationalized system of units and \[

\frac{e^2}{\epsilon_0\hbar c}\sim 0.092

\] which is already rather close to one. Moreover, you could write the QED Lagrangian in such a way that \(e\) appears in the first power. So a natural quantification of the strength of the force could be the square root of the number above \[

\frac{e}{\sqrt{\epsilon_0\hbar c}} \sim 0.303

\] which is "really" of order one. But these were high-school-level numerological games that don't reflect the actual expertise of a particle physicist well. The real reasons why it's natural for the fine-structure constant to be this small are different. In fact, it's more natural to express the strength using \(e^2\) and not \(e\); and it's more natural to divide this \(e^2\) by \(4\pi\) than not to do it. In fact, quantum loops naturally add an extra \(1/16\pi^2\) which makes the unnaturalness of \(\alpha\) worse, not better.

However, in the electroweak theory, \(\alpha\) and electromagnetism are no longer fundamental. They are produced as a mixture of two interactions, those mediated by the \(SU(2)_W\) and \(U(1)_Y\) gauge fields, respectively, and the extra angle determining the mixing – the Weinberg weak angle – is another source of the potential smallness of the low-energy fine-structure constants such as the electromagnetic one.



These muscles look a bit unnatural and I admit, they are unnatural – it is a Halloween outfit – but some people have very similar natural muscles, anyway.

Moreover, we know that \(\alpha\) should better not be too close to one – too high – because in that case, the coupling could diverge at slightly shorter distances (Landau pole, inconsistencies of the QFT) or slightly longer distances (confinement of a source). None of these things qualitatively agrees with the long-range electromagnetic force as we know it – we know it as an interaction that equally acts on a wide variety of objects and scales – which are reasons to expect that the electromagnetic fine-structure constant should be sort of significantly smaller than the maximum or natural value.

The comments above are vague reflections of rudimentary particle physics. A deeper knowledge of the correct short-distance theory could allow you to say much more. So I wouldn't be surprised at all if some dimensionless parameters encoding the soft supersymmetry breaking were found to be \(0.0001\) or smaller. On the contrary, I do expect such values to appear rather often. They only look unnatural if you believe the roughest, most naive probability distribution for these parameters. Any kind of better knowledge is bound to make some "natural candidates for preferred values" and their vicinity more likely. Zero is an extremely special point in the interval and there may exist many mechanisms and/or arguments that favor it or that favor its vicinity. If you say that you want to be indefinitely impressed by the relative smallness of a parameter, you're de facto saying that you don't want to learn about a more accurate physical explanation of these parameters and the dynamics that underlies them – more accurate relatively to the stupidest, roughest possible theory in which all parameters are equally likely.

When phenomenologists were solving the naturalness problem – effectively why the Higgs boson is so much lighter than the Planck scale – they focused on the theories that add new physics such as SUSY or technicolor very close to the scale of the Higgs mass. So the general belief is that any theory that makes the Higgs mass look natural must predict new particles whose mass is very close to the Higgs mass.

Even though I do realize that scalar masses may be produced or modified by pretty much any process, i.e. they are unprotected, I don't believe that this is inevitable. There are lots of examples in particle physics where one produces a small mass parameter without adding new particles that are equally light. An obvious example is the seesaw mechanism for the tiny neutrino masses. The neutrino masses that are generated in certain models are of order\[

m_\nu\sim \frac{m_{EW}^2}{m_{GUT}}

\] so they're smaller than the electroweak scale by the same factor by which the electroweak scale is amaller than the grand unified scale. Even though I appreciate that the lightness of the neutrino has been helped by the chiral symmetry, I am not aware of proofs of no-go theorems that would say that nothing vaguely similar is possible for the Higgs mass. In general, supersymmetry links the light Higgs to a comparably light higgsino (whose mass may be naturally light due to the same chiral symmetry as the neutrino) but other principles (symmetries and/or their stringy alternatives) or more specific types of SUSY may say more than that and they may favor a very light Higgs even in the absence of a "truly comparable in mass" higgsino.

So if you imagine that the success of the Standard Model will continue during or after the \(13\TeV\) LHC run that will begin in April 2015, it would mean that we will have a proof of some 1% fine-tuning in Nature. That's great but it will only be evidence that our naive, egalitarian, uniform probability distribution is no good – and rather weak evidence, for that matter. If there's still a 1% or 0.1% probability that such a smallness occurs by chance, its appearance is a 2.5-3.5-sigma signal supporting "something new". Moreover, we're not really sure what this "something new" is, not even approximately. Let me say in advance that if the LHC agrees with the Standard Model in 2015, I won't think that the multiverse will have been established; such a conclusion would seem totally premature to me.

People have spent $10 billion and many of them expected huge new results – because a smaller percentage of them have promised some huge new results – but there has never been a reason to be really certain that new physics (aside from the Higgs) would have to appear at the LHC. The LHC may be expensive but it brings us nowhere near the fundamental scale. With the 2012 LHC data, we're just 7% closer to the Planck scale than we were before the LHC! (It's on the log scale; on the linear scale, we have made almost no progress whatsoever.) Nothing fundamental has really changed about our inability to experimentally probe Nature at the fundamental scale. And the idea that some new physical phenomena would "have to" occur at the LHC has always been more wishful thinking (plus promises used to convince everyone that a new collider has to be built) and less solid, justified reasoning.

So for various reasons, dark matter and some naturalness bias, I still think that it's slightly more likely than not that the LHC will start to see new physics in 2015. So far, it has agreed with the Standard Model almost perfectly. Since yesterday, after nearly one month, the LHC experimenters began to release a huge package (dozens) of new papers (see the CMS, ATLAS hyperlinks in the right sidebar of this blog). I've gone through these papers and everything agrees with the Standard Model. One of the bins somewhere showed a 2.4-sigma excess and I won't even tell you where it was – somewhere in a \((180\GeV,200\GeV)\) bin – because given the large amount of channels and bins, an excess of this magnitude is very likely to appear.

Some of the tests of the Standard Model are somewhat impressive. For example, while I was writing this text, CMS tweeted that a new rare decay has been spotted.

If there's no experimental breakthrough and no theoretical revolution that will immediately and convincingly change our opinion about what is right around the corner behind the Standard Model, the status quo will simply continue whether you like it or not. In particular, some kind of a supersymmetric scenario remains the most likely candidate for new physics that will be observed on a sunny day in the future. In fact, we have repeatedly argued that supersymmetry's relative odds have increased due to the "negative" LHC data so far. But without a theoretical revolution, we can't really know when the Standard Model will finally break down. It's like throwing dice: every year in which the LHC is running, when you get a 6 (or perhaps 5 or 6), the Standard Model collapses. It may take quite some time. It is completely natural for such things to last some time.

The lightness of the Higgs combined with the evidence of no new particles with similar masses would strengthen - and has already strengthened – the proposal that we should think about particle physics in the multiverse framework. But I don't think that this strengthening has a chance to become a "completely dominant" paradigm in a few years or a decade. Whether we like it or not, the LHC has no magic bullet to be a game-changer and the status quo is bound to continue with minor gradual modifications if no game-changing discoveries are made.

And that's the memo.

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New miraculous ways how F-theory achieves gauge coupling unification

F-theory phenomenomenology has been described in dozens of TRF articles, e.g. these.

Initiated by Vafa et al. less than a decade ago, this formally 12-dimensional approach to particle physics combines some of the fanciest higher-dimensional stringy geometric methods with those of braneworlds to make predictions in which particle physics is somewhat naturally "decoupled" from the four-dimensional gravity and in which the properties of particle physics are somewhat different and thoroughly geometrized as (often degenerate) eight-real-dimensional complex shapes.



Today, an interesting hep-ph string-inspired paper was written by James C. Callaghan, Stephen F. King, George K. Leontaris:

Gauge Coupling Unification in E₆ F-Theory GUTs with Matter and Bulk Exotics from Flux Breaking

F-theory models like to predict large grand unified gauge symmetries to start with. In the case of \(E_6\), one finds fields in the "bulk" which transform in the adjoint, 78-dimensional representation of this exceptional Lie group. And there are other fields localized on "matter curves" that transform in the fundamental, complex 27-dimensional representation of \(E_6\).

We're used to say that whenever we add some generic extra light fields to the Minimal Supersymmetric Standard Model (MSSM), we modify the running of the gauge couplings which destroys the wonderful numerical coincidence that many of us like so much, the gauge coupling unification.




What's going on? The gauge couplings \(g_1,g_2,g_3\) of the \(U(1),SU(2),SU(3)\) factors of the Standard Model group aren't quite dimensionless constants. Due to the quantum loop effects linked to the renormalization group, they slowly – essentially logarithmically – evolve with the characteristic energy scale:\[

\frac{1}{g_{1,2,3}^2 (E)} = \frac{1}{g_{1,2,3}^2 (E_{EW})} + B_{1,2,3} \ln\zav{\frac{E}{E_{EW}}}.

\] So the three inverse squared couplings are linear functions of \(\ln(E)\), the logarithm of the typical energy scale of the processes. We measure their values at the electroweak scale and extrapolate them to the high energies via the calculable slopes \(B_{1,2,3}\).




We effectively draw three lines in the energy-coupling plane. Each generic pair of lines intersects somewhere but three random lines usually don't intersect at a single point. Instead, they produce three pairwise intersections.

And that's indeed the case of the Standard Model. The three pairwise intersections are sort of close to each other, near a high-energy slightly sub-Planckian scale, but they're distinguishably separated.

However, when you include the superpartners of all Standard Model particles and the extra Higgs fields needed to produce the Minimal Supersymmetric Standard Model, the quantum loops involving the new particles in the Feynman diagrams modify the slopes and the result is that the three lines pretty much exactly intersect at a high value of \(E\) which we may define to be the GUT scale.

(The hypercharge \(U(1)\) coupling constant has to be rescaled by the right factor of \(\sqrt{3/5}\) which follows from the actual way how this \(U(1)\) is embedded into GUT groups such as \(SU(5)\) or larger ones.)

This coincidence had an a priori chance smaller than 1-in-100 to yield a happy end. Some people exaggerate how powerful this numerical coincidence is (note that only one real number has to be adjusted or to naturally have the right value for the third line to hit the intersection of the first two, to present it in one particular way) but it is fair that this coincidence is as strong as a 2-sigma excess, perhaps a larger one, that seems to support the idea of the gauge coupling unification with the minimal MSSM spectrum near the \(\TeV\) scale.

When you add (or remove) generic particles from the MSSM, chances are that the unification goes out of the window.

However, the authors of the new paper I just linked to show that F-theory is capable of adding new exotic fields. Some of them are living in the bulk, i.e. arise from the 78-dimensional representation, some of them are living on the matter curves i.e. arise from the 27-dimensional representation. But their contributions to the mismatch sometimes cancel so that the gauge coupling unification is restored. The unification wouldn't work if you only added the bulk exotics or if you only added the matter curve exotics but if you add both, it just works. As far as I understand, this restoration of the gauge coupling unification occurs despite the fact that the added fields don't form complete representations of the GUT group – which is a simple way how to keep the unification undisturbed.

Because of the minimality, the MSSM is often viewed as the canonical choice – although some people have already switched to different favored models such as the NMSSM (MSSM with an extra chiral superfield \(S\) which is just the higgsino parameter \(\mu\) promoted to a field). But the results of this paper show – using my words – that if you love the MSSM because of the happy coincidence with the gauge coupling unification, you should love several classes of the F-theory models as well. In fact, when symmetries are broken by the flux which is the "flagship" mechanism in the F-theory model building, the unification is restored rather generically.

And those models do predict new exotics at the \(\TeV\) scale so if they're true, things get extremely interesting at the LHC approximately in 2015. I should mention that these E6SSM models tend to complete the leptons and quarks to a complete 27-dimensional representation of \(E_6\) which is really wonderful.

We may see. Stay tuned.

A few words about another paper by Don Marolf and Joe Polchinski,

Gauge/Gravity Duality and the Black Hole Interior.

It's disturbing because I feel that I have heard these arguments several times and they're still equally wrong. They claim that the existence of firewalls may be proven even without a near-maximal entanglement. Joe has written me the argument almost a year ago but it is based on a flawed assumption that the microstates with excited and unexcited infalling modes are equally represented. In reality, among microstates of a black hole with the mass \(M\pm \delta M\) (and when talking about genericity of microstates, it's very important to clearly declare which set of microstates or which density matrix we are talking about!), the microstates which predict \(N_a=0\) for generic low-energy freely infalling modes are exponentially more represented than those for which \(N_a\gt 0\) – because the cleaned, empty black hole is the result of stabilization and thermalization that was gradually increasing the entropy of the former star towards the maximum. So there's no contradiction between getting \(N_a=0^+\) on one hand and preserving the (approximate) thermality of the \(b\)-modes on the other hand.

They also try to challenge the ER-EPR correspondence by the comment that EPR-entangled states with generic phases don't admit a smooth ER-bridge visualization. Well, if you add generic phases, it's like adding generic excitations (local, low-energy, but also stringy or high-energy) into the Einstein-Rosen bridge, as Maldacena and Susskind also rather explicitly said, or at least I did. Of course that the clean, simple wormhole-like geometries describing entangled states are sort of special and rare, and so are the corresponding EPR-entangled states. But the rest may be obtained by "excitations" of these special states much like a generic Fock state vector may be obtained by adding with creation operators on the vacuum. I don't understand what's Marolf's and Polchinski's problem with that. This observation doesn't seem to weaken the claim that a loophole in the firewall "proof" has been demonostrated.

One more comment. The ER-EPR correspondence is a rather explicit, cute new way to think about certain microstates but it is clear that this loophole existed even without this particular geometrization of the entangled states. So I think it's obvious that the Maldacena-Susskind, while very exciting, is in no way "necessary" to see that the AMPS(S) papers are invalid.

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CMS: \(2.93\sigma\) hint of a second Higgs boson at \(136.5\GeV\)

Today's sensation is tomorrow's calibration. Or: Today's discovery is tomorrow's background. Ladies and Gentlemen, it's my pleasure to tell you that we are finally living in the tomorrow in the sense of these proverbs. CMS has finally published a paper that incorporates the \(125\)-\(126\GeV\) Higgs boson into the background.

Properties of the observed Higgs-like resonance decaying into two photons (CMS PAS HIG-13-016)

ATLAS and CMS are doing a superb precision work. One of the consequences is that their papers have been found to agree with the Standard Model immensely well. In fact, we haven't seen virtually any \(2\sigma\) excesses. One could argue that the number of false positives in other experiments than ATLAS and CMS – bumps that would fill many physicists with a "hope" that turned out to be unjustified – was much higher than 5% and the reason was that these experimenters were just sloppier than ATLAS and CMS.

But neither new physics nor flukes can be denied and confined indefinitely. The paper above which was released today is an example.




They have studied how many Higgs bosons are produced that decay into two photons, \(h\to \gamma\gamma\), and the final number agrees with the predictions of the Standard Model within one sigma. This invalidates some "hopes" that the LHC had seen way too many diphoton decays a year ago or so. This particular new paper can't exclude, based on the spin-related measurements of the diphoton processes only, that the Higgs particle is a graviton-style spin-two particle but there are other experimental and especially theoretical ways to de facto exclude the possibility.




But while the old false hope has been killed, there's a new one. They made a search for another Higgs-like resonance aside from the \(125\)-\(126\GeV\) Higgs boson that has already been discovered. And here is the main graph showing the results:



It's Figure 3 – in the paper, you also see a combination of these two graphs at the top. The left graph requires the Higgs to come from the vector-boson fusion while the right graph above is from the vector-boson associated production only. If my understanding is right, these two graphs should visualize two totally disjoint sets of proton-proton collisions.

What you see on the left graph is a rather clear excess near \(m_H=136.5\GeV\), as the paper quantifies the location. We're told that the local significance of this extra peak is \(2.73\sigma\). That's far from a discovery but it's a lot. The right graph should come from different events but it also has a \(2.15\sigma\) excess, as they quantify it. What is the mass of the would-be new particle that would follow from this second bump if it were real? Believe me or not, it is\[

m_H = 136.5\GeV.

\] Quite a coincidence, right? If you need to know,\[

\sqrt{2.73^2+2.15^2} = 3.47.

\] In some sense, unless I am making a mistake, the total local significance of the excess is a brutally tantalizing \(3.5\sigma\). That's a lot. Well, their own combination of both parts of Figure 3, namely Figure 2, quotes the overall local significance as \(2.93\sigma\). I can't explain you where the discrepancy comes from but we're near \(3\sigma\), anyway. (Ulrich Ellwanger explained to me that the significance \(3.5\sigma\) is an overestimate because the two components share a systematic error.)

Needless to say, minimal and rather minimal supersymmetric standard models of particle physics often predict that along with a Higgs boson below \(130\GeV\), there should be another equally CP-even neutral Higgs boson above \(130\GeV\). The other three Higgs bosons among the five God particles of the MSSM are two charged ones; and one CP-odd boson \(A\).



Only the left Higgs, one with the mass \(125\)-\(126\GeV\), is clearly real at this point. The other Higgses with different masses, indicated by differently stuffed bellies, are rather likely to turn out to be just mirages.

In recent years, it has become popular to assume that the other Higgses predicted by supersymmetry is much heavier than the Higgs boson found almost exactly one year ago. But the possibility that their masses are really close hasn't really been excluded yet. Under a certain paradigm, it actually seems extremely natural for the two Higgses to be distributed quasisymmetrically with respect to the \(130\GeV\) boundary between "light" and "heavy" Higgs bosons which supersymmetry likes to draw.

It may be a good idea to wait for the analogous paper by ATLAS (or is it already out?). If it provided us with some \(3.5\sigma\) evidence as well, the local informal significance of this new peak could alredy surpass \(5\sigma\). And that would start to be really interesting, well before the \(13\TeV\) run that will begin in April 2015. It could be a good enough reason for Jester and others to buy some new underwear.

Fascinatingly enough, a \(3.5\sigma\) excess at the precisely the same mass, \(136.5\GeV\), seen in the analogous CMS diphoton graphs was being debated already one year ago (in the wake of the first official Higgs discovery) when a much (2.5 times) smaller dataset, \(5.1+5.3/{\rm fb}\), was available. The significance should have dropped but it stayed the same.

Update: Pages 5-6 of some ATLAS presentation suggest that ATLAS has seen nothing over there. There's a nearby excess at \(141\GeV\) or so but that's already significantly different, despite the fact that ATLAS tends to report the masses in the diphoton channel that are up to \(3\GeV\) higher than those of CMS. But one needs \(4.5\GeV\) here... ;-)

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Jacques Distler on his lost new physics bet

Jacques Distler of Austin lost a $750 bet to Tommaso Dorigo and wrote an article about it:

Guest Post: Jacques Distler, Why I Lost $750 On New Physics At The LHC (original text)

They ultimately agreed that Distler wins if a new-particle-like 5-sigma discrepancy from the Standard Model is announced within 12 months after the moment when the LHC has had accumulated 10 inverse femtobarns of collisions (the energy was allowed to be just 8 TeV, it seems). Gordon Watts supported Distler's bet by another $250 so if he concedes as well, and I think he should, Dorigo should be $1,000 richer because the conditions were fulfilled several weeks or months ago.



It was a risky bet for both sides. Would Distler make a similar bet on the 2015 run?

The answer, I think, is: not unless you were willing to give me some substantial odds (at least 5–1; if I think about it, maybe even higher).

Well, my bet against Jester turned out to be effectively a bet on the early 2015 run because we're talking about 30 inverse femtobarns which haven't been accumulated yet (we're around 27) and our bet is 100-to-1 which means that I may win $10,000 but will lose $100 only. You see that your humble correspondent was expecting better conditions and when it came to the assertions, he was more cautious, but just by a factor of three, than Distler and Watts.




I think that my odds of winning remain substantial because the 13 TeV collision energy of events that will start to be produced in April 2015 opens a whole new game.

If you keep your energy constant, it's pretty much necessary to have at least 3-sigma excesses if you want to see 5-sigma excesses at a doubled or tripled total luminosity. After all, the results are changing quasi-continuously if you're adding new collisions to your dataset. When the luminosity jumps 6 times or so, you get "completely new data" because 5-sigma deviations in the new data may easily come from bumps that were expected to be smaller than 2 sigma, and therefore invisible, in the 6 times smaller dataset.




However, with that doubling in the energy, the rules are completely different because particles of certain masses would be almost impossible to discover at 8 TeV but they may be instantly discovered at 13 TeV, perhaps after an inverse femtobarn of data if not earlier. So Jester of Resonaances cares about his $10,000, he shouldn't sleep well until mid 2015 or so. ;-)

Yes, I surely think that even with all the facts we know, the probability that new physics will be discovered in the early 2015 run is substantially greater than 1%. In other words, my position in the bet is worth jealousy. The new particles that may be found may still be much much lighter than 1 TeV. Tons of scenarios with the LSP at 130 GeV (like in the Fermi hints) or even 8.6 GeV (like in the dark matter direct search experiments) remain viable.

Jacques starts his article with some memories of Steven Weinberg on C-SPAN talking about the SSC two decades ago; and about the way how energy is divided between the partons inside the proton so that the actual energy scale you may easily probe is smaller than the proton energy (except for an ever smaller fraction of the collisions in which the proton energy is increasingly more concentrated in one parton).

Distler ends up by saying that the probability that the LHC will ever see new physics has dropped significantly; and the conditional probability that the new physics, assuming that it will be found, will be supersymmetry has increased because the other types of new physics were disfavored much more rapidly. I agree with those statements assuming that the word "significantly" is understood in my way. It's significant but surely not totally qualitative. Maybe there would be a disagreement between Jacques and me if the meaning of the words were clarified. The disagreement could boil to this statement by Jacques:

Still, there are (or were) lots of scenarios with new physics, accessible to the LHC. And theorists, being perennial optimists, put a lot of effort into exploring those scenarios.

I disagree and I have always disagreed with this definition of optimism of a theorist; it is a bias in the literature, not legitimate optimism. A theorist thinking like myself is equally pleased if Nature obeys nice laws with a new particle waiting at 150 GeV; or nice laws with a new particle waiting at 3,000 GeV. If you're equally pleased by both possibilities, you can't say that believing in one of them is "optimism" and believing in the other is "pessimism". Preferring the former possibility – to the extent of selectively writing papers about the first possibility – is just wrong and if the bulk of phenomenologists are acting in this way, it is (and actually was) a case of group think. An experimenter dreaming about his own discovery – assuming that the experimenter's job is to maximize the probability (times importance) of a discovery – may call the belief in low-lying new physics fruits "optimism". But a theorist's job is to find the truth so he simply can't afford the asymmetric perception of different, equally justifiable or likely scenarios. There are lots of "big desert-like" scenarios where – up to a possible exception of SUSY – nothing happens between the electroweak scale and the Planck scale (or at least the GUT scale). I think they're pretty in their characteristic way so the belief that they're true can't be called it a "pessimistic belief".

"Hopes" in the new physics around the corner were always (mostly) motivated by some phenomenologists' desire to increase their odds to get famous quickly (so claiming that this bias was due to their "virtue of optimism" is completely obscuring the true motivations) and the impact of this desire on the literature may be classified as a distortion of the facts because the composition of the literature reflects their desires rather than available facts and it's always wrong for theory literature to be skewed by similar non-fact-based pressures. So this bias describing "new physics around the corner" was surely wrong and I always thought it was wrong but this wrongness doesn't imply that the LHC will never see new physics. Jacques Distler may switch to an opposite extreme but this won't make new physics at the LHC in 2015 impossible just like his "optimism" didn't guarantee early LHC discoveries of BSM physics.

I believe that as the LHC is increasing the total luminosity and/or energy kind of exponentially, the probability of a new discovery per unit time is staying pretty much constant because a sensible distribution of physical phenomena between the low-energy scales and the Planck scale is pretty much uniform on the log axis (you may even estimate the density of particles per decade from the particles we already know). The idea that if the LHC finds something new, it has to happen immediately, is unwarranted. Well, the LHC made a qualitative leap at the very beginning because it had more energy than any earlier experiment. It only found the Higgs boson as the quasi-new physics. But that doesn't mean that almost the whole space of possibilities has been exhausted. Now, the LHC is moving the frontiers of science more gradually.

It's plausible that LUX will find the sub-10-GeV dark matter particle before the end of 2013 i.e. years before the LHC will say anything about it. The two years' vacation at the LHC may substantially shrink the collider's competitiveness in discovering new physics.

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