To a few others, however, the LHC data appears instead to provide feeble but increasing hopes for a confirmation of their favoured theory. One of these few lucky theorists is Dimitri Nanopoulos. I had the privilege to shake Dimitri's hand last December, as I attended a seminar he gave (in greek!) to the greek community in Geneva. It took me very little time to realize he is an optimist, and a contagious one: charisma is the word. The spark of his eyes broadcasts his positive attitude and his enthusiasm on the matter quite effectively and convincingly.
In his seminar, not at all like I had expected it, Nanopoulos quickly educated his listeners with a crash course on the basics of fundamental physics and modern-day astrophysics, and then spent a significant part of his talk explaining the general ideas behind his pet model, no-scale
F-SU(5). I would do a bad service to Nanopoulos, to F-SU(5), and to you if I attempted to summarize the model here, so I will just define it as a theoretical construction including the idea of SU(5) grand-unification and two sets of Supersymmetric multiplets of vector-like particles (so-called "flippons"), fulfilling the constraints of no-scale supergravity. If the above sounds utterly obscure to you, let me welcome you to the club.
Nanopoulos and collaborators have published several articles on this model in the recent past. One which I will mention here is "Profumo of SUSY", arxiv/1111.4204, where the scent came from two multijet event searches produced by the two LHC experiments; the interest there was focused on the very high jet multiplicities, from 7 to 9 jets, which Nanopoulos described as a particularly clean probe of his specific model, which would distinctively populate those high multiplicities due to the mass hierarchy of supersymmetric states it predicted - in particular, a light stop ang gluino.
A few days ago the same analogy between the first potential hints of particle excesses in five recently published LHC analyses (particularly in signatures including a smaller number of jets, but enriched with b-tags and leptons) and the good smell of delicacies cooking in the LHC oven was used in the title of his latest preprint, "The Aroma of Stops and Gluinos at the sqrt(s)=7 TeV LHC", arxiv/1203.1918.
The model advocated in the paper is interesting from a technical point of view because of the recent hint that the Higgs boson mass might be in the 125 GeV ballpark. This mass would normally point to large masses of Supersymmetric particles -a 10-20 TeV universal scalar mass is mentioned in the paper. However, the presence of flippons in F-SU(5) would give an upward contribution to the mass of the lightest Higgs of 3-4 GeV, thus lowering the typical scale of SUSY particles. So F-SU(5) lends itself to verification more aptly than other MSSM scenarios.
The distinctive hierarchy implying a light stop and gluino would allow very distinctive signatures at the LHC, and the object of the paper is to show that the recent LHC analyses in fact are consistent with the model. To do so, authors study the seven different signatures published by ATLAS and CMS, and with the results of those searches put together a global chisquare, which is then compared to predictions of the Standard Model alone and of the F-SU(5) scenario. Of course the whole study cuts some corners here and there, both because it would be too complicated to consider in their entirety the results of the various experimental searches and because the publications sometimes lack to provide all the information that would be required; indeed, only the event counts of the final selected candidates observed in the various analyses are used in the fit. Still, one may look with some curiosity at the summarized results in the figure below.
In this complicated plot one sees the stop and gluino masses in the abscissa, and the relative chisquare of the global fit on the vertical axis. The "golden strip" and "silver strip" shown as vertical bands indicate the values of stop and gluino masses which are in best agreement with the collection of Standard Model observables (including top mass, g-2 results, Z-pole observables, etcetera). The purpose of the figure is to show that if one marries F-SU(5), then the past data implications for the model parameters (green line describing the global χ2) put it exactly in the right ballpark with the observed event counts of the LHC searches.
In the words of the authors,
Although we cannot argue for incontrovertible evidence of SUSY peeping beyond the Standard Model veil, we can safely suggest that No-Scale F-SU(5) is a better global fit to the data than the SM alone, and moreover that its predictions appear to be meaningfully correlated with observed low-statistics excesses across a wide variety of specialized search strategies, while gracefully avoiding devastating overproduction where events are not observed. This is a strong statement in an era when the portion of phenomenologically viable MSSM and mSUGRA constructions is diminishing rapidly, choked out by inconsistency with the Higgs measurements and advancing squark and gluino exclusion limits.
And later on they conclude:
The damage exacted onto the supersymmetric model landscape by the swiftly progressing LHC constraints has been severe. The tension between the growing likelihood of a 125 GeV Higgs boson mass, developing CMS and ATLAS exclusion zones, and a supersymmetric spectrum light enough to be within reach of the current operational phase of the LHC has greatly altered the conventional wisdom as to how a discovery of supersymmetry would manifest at the LHC. While the validation prospects for almost all prospective models has greatly withered, the outlook for F-SU(5) appears to have in fact brightened; in stark contrast, it is perfectly capable of simultaneously striking each of these three targets. A rare feat nowadays, indeed.
Despite my scepticism at the correctness of F-SU(5) or other SUSY theories, I plaud at the optimistm and positive attitude of the authors, who go "all in" betting on the 2012 LHC datasets to increase those feeble scents of F-SU(5) they have detected in past data. I also like their
admission that in general the picture looks unpromising for SUSY scenarios after the first serious year of LHC running. And finally, I am led to recall the surprising, uncompromising, funny statement that Dimitri Nanopoulos made toward the end of his talk in Geneva last December:
if his model is falsified, he will retire in a greek island, to spend his time fishing. While I do believe F-SU(5) will indeed be falsified soon by the CMS and ATLAS searches, I can only hope that Nanopoulos will neglect his own vow, and he will instead continue to search with
enthusiasm for viable alternatives to the Standard Model Boredom which has dominated the last forty years of particle physics, and threatens to continue doing so in the XXIst century!
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