Monday, December 21, 2015

Supersymmetry may be taking over the \(750\GeV\) model building

Sbinos and the NMSSM officially run

In the fourth dose of preprints, at least seven new hep-ph papers with possible explanations of the \(750\GeV\) resonance have been published, bringing the total number of theory papers on the bump to 43 unless the Dutch blog has missed some papers. The model builders have created 43 parallel universes in which the (uncertain to exist) resonance has an explanation.

One paper discusses an obvious proposal, perhaps the "first one" that many of us would say, that the new particle is a new Higgs boson. It should be a singlet, they say. Another paper wants the new particles to couple to the Standard Model only via the WZW anomaly.

A paper by Alex, Alexandre, and a non-Alex says that the new particle \(S\) is almost certainly an \(S\)-cion, something I have never heard of, which has far-reaching implications for the hierarchy problem and amazing completions etc. except that the model they discuss is nothing else than the ordinary scalar coupled to the gauge bosons and the paper seems to be basically a signature-driven paper with no deep theory ideas.

A new paper proposes that the newly discovered particle is a dilaton but it seems to use a more CFT-based description of similar physics as the recent paper about the radion.

And the last hep-ph paper today suggests that there is a third particle produced aside from the two photons, a fact that could explain the apparently large width.

But there are finally some "mostly ordinary" supersymmetric models that attempt to explain the new particle if it exists, [11] and [21]. The first paper I mention basically describes the NMSSM, the next-to-minimal supersymmetric standard model. The minimal model, MSSM, has been agreed not to be appropriate for predicting this particle.

But this paper agrees that the NMSSM seems enough. More precisely, they are only describing some non-supersymmetric subset of the NMSSM field content. They need a new scalar particle; and they need new colored scalars. Those may be embedded in the NMSSM as the new Higgs bosons and the ordinary squarks, they argue.

To say the least, the discovery of the resonance would mean a clear transition of the supersymmetry model building away from MSSM towards NMSSM and similar models. However, I must also point out that there are the three sgoldstino papers which elaborate on a much more non-standard supersymmetric model building, one with the sgoldstino. These models would probably imply that the dark matter is composed of very light gravitinos. There are many reasons why I think that this character of dark matter is much more likely than the composition of SUSY hep-ph papers indicate. The gravitino is "special" and it's nice to assign it the special cosmological role; the direct search for neutralinos seems to exclude a significant portion of the parameter space by now; a tiny gravitino mass comparable to the neutrino meV-like masses could explain the tiny cosmological constant if the latter turns out to be about the fourth power of the gravitino mass and the larger contributions may be ignored for some reason; and the sgoldstino discovery would simply make gravitinos much more central, too.

The second supersymmetric paper on the diphoton resonance says that it is a sbino. It was written by Linda Carpenter et al. (a good surname during Christmas although Jesus was more than a carpenter LOL.) Aside from the NMSSM and the sgoldstino/gravitino-based supersymmetric models, this "sbino" explanation builds on another part of supersymmetric model building that I consider significantly understudied, the Dirac gauginos.

As discussed in numerous TRF blog posts, supersymmetry may be de facto enhanced to \(\NNN=2\) in the sector of gauge bosons. It means that the gauge bosons don't have just one gaugino superpartners but two; they may be combined to Dirac gauginos (as opposed to the normal Majorana gauginos that only have 1/2 of the degrees of freedom). We have just doubled the fermionic degrees of freedom. Supersymmetry requires a boson-fermion numerical matching so we must also add new bosons. They can't be spin-one bosons anymore because there can only be one gauge boson for a symmetry. Instead, we must add a new scalar, the sgaugino.

For the \(SU(3)_c\), \(SU(2)_W\), and \(U(1)_Y\) groups, these new scalars may be called the sgluino, swino, and sbino. The latter one, the sbino, is said to be a viable candidate for the \(750\GeV\) diphoton resonance.

Once again, cute supersymmetric models that might explain the resonance nicely exist. We don't know whether the resonance is real yet. But if it is real, my impressions that the minimal models, especially the MSSM with the neutralino dark matter, have been overstudied and the other interesting classes of SUSY models have been understudied will probably be vindicated although it is not quite clear which of the less popular models, if any, would be relevant for the explanation of the resonance.

Merry Christmas! You may think that physics trolls are annoying but once upon a time, a physics troll saved Christmas – against the gifts that were sucked away from the Earth ;-) by gravity. What I find even more amazing than this troll's service to Santa Claus is that the video has received over 100,000 views.

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