Recent rumors supposedly coming from theorists at Harvard indicating that today would be the day that an announcement would be made of first evidence for a superpartner of a top quark have just been shot down. The talk at CERN on recent ATLAS searches for such a signal shows that nothing was found. An example of new limits is that if stops are produced via gluinos, the gluino has to have mass greater that 650 GeV and the stop a mass greater than 450 GeV.
Over the past year the LHC has conclusively falsified pre-LHC predictions that strongly interacting superpartners would easily be seen in the early data, with typical bounds on gluino masses now up to 1 TeV or so. One way to evade this conclusion has been to argue that the first two generations of squarks are quite heavy, with only the sbottoms and stops accessible to the LHC. A typical example of analysis of scenarios of this kind can be found here, where the conclusion is that naturalness requires that the mass of an stop be less than 400 GeV, and the mass of a gluino less than twice the mass of the stop. This is now starting to be in significant disagreement with the data.
The ATLAS analysis uses 2 fb-1 of data, with the promise of updated results using the full 4-5 fb-1 coming soon. The details of the new analyses were made public today here, here and here. For some background, see the latest posting at Resonaances. I hear that similar analyses now completed by CMS, with the full 2011 dataset, also show nothing. This week the earliest of the Winter conferences is going on, at Aspen, and tomorrow there will be talks updating the LHC SUSY situation from ATLAS, CMS, and theorist Matt Reece.
The LHC has done an impressive job of investigating and leaving in tatters the SUSY/extra-dimensional speculative universe that has dominated particle theory for much of the last thirty years, and this is likely to be one of its main legacies. These fields will undoubtedly continue to play a large role in particle theory, no matter how bad the experimental situation gets, as their advocates argue “Never, never, never give up!”, but fewer and fewer people will take them seriously. As always seemed likely, the big mystery the LHC will solve will be that of the Higgs: is it really there, and if so does it behave as the Standard Model predicts, or does it do something more interesting? Unfortunately we’re going to have to wait a while longer for more news on that front.
@ Matt, for stringy models with split spectra I’d recommend checking out this paper http://arxiv.org/abs/hep-th/0701034 or the more general version of the same construction http://arxiv.org/abs/0810.3285
@Matt, I must correct one of my previous statements. After a more careful checking, it turns out that for moduli-dominated SUSY breaking when the moduli F-term contributions nearly cancel the -3M_{3/2}^2M_{Planck}^2 term in the scalar potential, the cancellation of the leading contribution to the scalar mass squareds a la LV scenario of Joe et al does happen for the G2 case as well! In Type IIB, the moduli Kahler potential is K=-2Ln(V) and the bifundamental chiral matter Kahler potential scales as 1/V^(2/3), where V is the CY volume, and these two things, when combined with moduli-domination and CC=0 constraint, lead to parameter p=1. In G2 compactification case, K=-3Ln(V) while the Kahler potential for fundamental chiral matter scales as 1/V, where V is the volume of the G2 manifold, and when combined with the assumption of moduli-dominated SUSY breaking and CC=0, also lead to p=1 and the suppression of the scalar masses! These cancellations look completely mysterious from the 4D point of view though. That said, the G2 vacua of Acharya et al do not have this feature and do exhibit a split spectrum because in that case SUSY breaking is not moduli-dominated.
MathPhys wrote:
The original Standard Model had massless neutrinos, and thus no neutrino oscillations. The new Standard Model has neutrinos whose masses and oscillations are described by the Pontecorvo-Maki-Nakagawa-Sakata matrix. I’m not sure how convinced the experts are that neutrino physics is adequately captured by this new Standard Model – I haven’t been keeping up with that.
No, that’d be going too far. Many astrophysicists believe there’s ‘cold dark matter’ made of some particle or particles not included in the Standard Model. Many believe in ‘dark energy’, which can be modeled simply by including a cosmological constant in Einstein’s equations, but might arise from some particles we don’t know. And many believe in ‘inflation’, which requires some physics beyond the Standard Model and general relativity.
In short, astrophysics and cosmology seem to require physics beyond the Standard Model and general relativity.
In addition to the excellent points made by John, one shouldn’t forget that a certain amount of CP violation is required in order to generate baryogenesis/leptogenesis. The Standard Model does not provide enough CP violation, and so presumably this is generated by new physics.
Eric,
Note that one thing which is not usually well known/advertised among particle physics/HEP audience is that there are modifications/extensions to GR which can potentially explain baryogenesis. Two examples are Einstein-Cartan-Kibble-Sciama theory(see http://arxiv.org/abs/1101.4012) and Chern-Simmons theory (see http://arxiv.org/abs/gr-qc/0308071).
so in that case you don’t need beyond SM physics, but we do need physics beyond SM+GR.
Eric,
Judging from the abstract from http://arxiv.org/abs/1101.4012, this is only a classical theory and the theory is supposed to apply at the very early universe, for which you absolutely need a quantum theory of this theory that also incorporates the SM, as well as any other possible interactions between this scale and the SM scale.
Just to be clear, this is the conventional wisdom and it may very well be true, but it isn’t an established fact. We don’t have a “real” quantum gravity theory yet, and don’t know what will ultimately describe the very early universe…